Make ShiftExistingBiomes available via API (#40)

* bug fixes

Fixes wrong new_y_min when shift_existing_biomes() shifts a biome below the nether floor,
find_surface_anchorPos() no longer assumes y=0 will be outside the nether.
Nil-reference fixed when a mods tries to register a portal after mods are finished loading, but the portal shape+material was already registered by another mod.

* Make ShiftExistingBiomes available via API

makes the ShiftExistingBiomes function available to other mods via the nether global, since it's not a simple function and biomes would also need to be shifted if another mod wants to add a second nether layer.

* Allow layers to extend the depth of nether effects

Mods can set/lower nether.DEPTH_FLOOR_LAYERS when creating a layer under the nether. This allows multiple layer mods to know where their ceiling should start, and to be included in the effects which only happen in the nether.

* document nether API

More of a tentative interop guide than an API.
Use snake_case for API functions.

.luacheckrc

@@ -2,10 +2,12 @@ unused_args = false
 allow_defined_top = true
 
 globals = {
+	"bucket",
 	"nether"
 }
 
 read_globals = {
+	"climate_api",
 	"core",
 	"default",
 	"DIR_DELIM",

README.md

@@ -1,9 +1,31 @@
-Nether Mod for Minetest, with Portals API.
+# Nether Mod for Minetest, with Portals API.
+
+Allows Nether portals to be constructed, opening a gateway between the surface
+realm and one of lava and netherrack, with rumors of a passageway through the
+netherrack to a great magma ocean.
+
+To view the options provided by this mod, see settingtypes.txt or
+go to "Settings"->"All Settings"->"Mods"->"nether" in the game.
+
+A Nether portal is built as a rectangular vertical frame of obsidian, 4 blocks
+wide and 5 blocks high. Once constructed, a Mese crystal fragment can be
+right-click/used on the frame to activate it.
+
+
+## Modders and game designers
 
 See portal_api.txt for how to create custom portals to your own realms.
 
-See settingtypes.txt or go to "Settings"->"All Settings"->"Mods"->"nether"
-in the game to view the options provided by this mod.
+This mod provides Nether basalts (natural, hewn, and chiseled) as nodes which
+require a player to journey to the magma ocean to obtain, so these can be used
+for gating progression through a game. For example, a portal to another realm
+might need to be constructed from basalt, thus requiring a journey through
+the nether first, or basalt might be a crafting ingredient required to reach
+a particular branch of the tech-tree.
+
+Netherbrick tools are provided (pick, shovel, axe, & sword), see tools.lua
+
+Nether Portals can allow surface fast-travel.
 
 
 ## License of source code:
@@ -27,22 +49,32 @@ SOFTWARE.
 
 ### [Public Domain Dedication (CC0 1.0)](https://creativecommons.org/publicdomain/zero/1.0/)
 
- * `nether_portal_teleport.ogg` is a timing adjusted version of "teleport" by outroelison (https://freesound.org/people/outroelison), used under CC0 1.0
+ * `nether_portal_teleport.ogg` is a timing adjusted version of "teleport" by [outroelison](https://freesound.org/people/outroelison), used under CC0 1.0
 
 ### [Attribution 3.0 Unported (CC BY 3.0)](https://creativecommons.org/licenses/by/3.0/)
- 
+
  * `nether_portal_ambient.ogg` & `nether_portal_ambient.0.ogg` are extractions from "Deep Cinematic Rumble Stereo" by [Patrick Lieberkind](http://www.lieberkindvisuals.dk), used under CC BY 3.0
- * `nether_portal_extinguish.ogg` is an extraction from "Tight Laser Weapon Hit Scifi" by damjancd (https://freesound.org/people/damjancd), used under CC BY 3.0
- * `nether_portal_ignite.ogg` is a derivative of "Flame Ignition" by hykenfreak (https://freesound.org/people/hykenfreak), used under CC BY 3.0. "Nether Portal ignite" is licensed under CC BY 3.0 by Treer.
+ * `nether_portal_extinguish.ogg` is an extraction from "Tight Laser Weapon Hit Scifi" by [damjancd](https://freesound.org/people/damjancd), used under CC BY 3.0
+ * `nether_portal_ignite.ogg` is a derivative of "Flame Ignition" by [hykenfreak](https://freesound.org/people/hykenfreak), used under CC BY 3.0. "Nether Portal ignite" is licensed under CC BY 3.0 by Treer.
 
 ### [Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)](https://creativecommons.org/licenses/by-sa/4.0/)
+ * `nether_basalt`* (files starting with "nether_basalt"): Treer, 2020
  * `nether_book_`* (files starting with "nether_book"): Treer, 2019-2020
- * `nether_portal_ignition_failure.ogg`: Treer, 2019
+ * `nether_fumarole.ogg`: Treer, 2020
+ * `nether_lava_bubble`* (files starting with "nether_lava_bubble"): Treer, 2020
+ * `nether_lava_crust_animated.png`: Treer, 2019-2020
  * `nether_particle_anim`* (files starting with "nether_particle_anim"): Treer, 2019
+ * `nether_portal_ignition_failure.ogg`: Treer, 2019
+ * `nether_smoke_puff.png`: Treer, 2020
 
 ### [Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)](http://creativecommons.org/licenses/by-sa/3.0/)
- * `nether_rack.png`: Zeg9
- * `nether_glowstone.png`: BlockMen
+ * `nether_glowstone`* (files starting with "nether_glowstone"): BlockMen
+ * `nether_nether_ingot.png` & `nether_nether_lump.png`: color adjusted versions from "[default](https://github.com/minetest/minetest_game/tree/master/mods/default)" mod, originally by Gambit
  * `nether_portal.png`: [Extex101](https://github.com/Extex101), 2020
+ * `nether_rack`* (files starting with "nether_rack"): Zeg9
+ * `nether_tool_`* (files starting with "nether_tool_"): color adjusted versions from "[default](https://github.com/minetest/minetest_game/tree/master/mods/default)" mod, originals by BlockMen
 
-All other media: Copyright © 2013 PilzAdam, licensed under CC BY-SA 3.0 by PilzAdam.
+### [Unlicensed but permission for inclusion by kovaszos_uborka](https://www.planetminecraft.com/member/kovaszos_uborka/)
+ * `nether_brick_deep.png` (edited by TenPlus1)
+
+All other media: Copyright © 2013 PilzAdam, licensed under CC BY-SA 3.0 by PilzAdam.

crafts.lua

@@ -0,0 +1,72 @@
+--[[
+
+  Copyright (C) 2013 PilzAdam
+  Copyright (C) 2020 lortas
+  Copyright (C) 2020 Treer
+
+  Permission to use, copy, modify, and/or distribute this software for
+  any purpose with or without fee is hereby granted, provided that the
+  above copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+  WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR
+  BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES
+  OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+  WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+  ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+  SOFTWARE.
+
+]]--
+
+minetest.register_craft({
+	output = "nether:brick 4",
+	recipe = {
+		{"nether:rack", "nether:rack"},
+		{"nether:rack", "nether:rack"},
+	}
+})
+
+minetest.register_craft({
+	output = "nether:fence_nether_brick 6",
+	recipe = {
+		{"nether:brick", "nether:brick", "nether:brick"},
+		{"nether:brick", "nether:brick", "nether:brick"},
+	},
+})
+
+minetest.register_craft({
+	output = "nether:brick_compressed",
+	recipe = {
+		{"nether:brick","nether:brick","nether:brick"},
+		{"nether:brick","nether:brick","nether:brick"},
+		{"nether:brick","nether:brick","nether:brick"},
+	}
+})
+
+minetest.register_craft({
+	output = "nether:brick_deep 4",
+	recipe = {
+		{"nether:rack_deep", "nether:rack_deep"},
+		{"nether:rack_deep", "nether:rack_deep"}
+	}
+})
+
+minetest.register_craft({
+    output = "nether:basalt_hewn",
+    type = "shapeless",
+    recipe = {
+      "nether:basalt",
+      "nether:basalt",
+    },
+})
+
+minetest.register_craft({
+  output = "nether:basalt_chiselled 4",
+  recipe = {
+    {"nether:basalt_hewn", "nether:basalt_hewn"},
+    {"nether:basalt_hewn", "nether:basalt_hewn"}
+  }
+})
+
+-- See tools.lua for tools related crafting

depends.txt

@@ -1,7 +1,9 @@
-stairs
 default
-moreblocks?
-mesecons?
-loot?
-dungeon_loot?
+stairs
 doc_basics?
+dungeon_loot?
+fire?
+loot?
+mesecons?
+moreblocks?
+climate_api?

init.lua

@@ -42,12 +42,18 @@ end
 
 -- Global Nether namespace
 nether                = {}
+nether.mapgen         = {} -- Shared Nether mapgen namespace, for mapgen files to expose functions and constants
 nether.modname        = minetest.get_current_modname()
 nether.path           = minetest.get_modpath(nether.modname)
 nether.get_translator = S
                      -- nether.useBiomes allows other mods to know whether they can register ores etc. in the Nether.
                      -- See mapgen.lua for an explanation of why minetest.read_schematic is being checked
 nether.useBiomes      = minetest.get_mapgen_setting("mg_name") ~= "v6" and minetest.read_schematic ~= nil
+nether.fogColor = {	           -- only used if climate_api is installed
+	netherCaverns = "#1D0504", -- Distance-fog colour for classic nether
+	mantle        = "#070916", -- Distance-fog colour for the Mantle region
+	geodes        = "#300530"  -- Distance-fog colour for secondary region
+}
 
 
 -- Settings
@@ -70,6 +76,19 @@ if nether.DEPTH_FLOOR + 1000 > nether.DEPTH_CEILING then
 end
 nether.DEPTH = nether.DEPTH_CEILING -- Deprecated, use nether.DEPTH_CEILING instead.
 
+-- DEPTH_FLOOR_LAYERS gives the bottom Y of all locations that wish to be
+-- considered part of the Nether.
+-- DEPTH_FLOOR_LAYERS Allows mods to insert extra layers below the
+-- Nether, by knowing where their layer ceiling should start, and letting
+-- the layers be included in effects which only happen in the Nether.
+-- If a mod wishes to add a layer below the Nether it should read
+-- nether.DEPTH_FLOOR_LAYERS to find the bottom Y of the Nether and any
+-- other layers already under the Nether. The mod should leave a small gap
+-- between DEPTH_FLOOR_LAYERS and its ceiling (e.g. use DEPTH_FLOOR_LAYERS - 6
+-- for its ceiling Y, so there is room to shift edge-case biomes), then set
+-- nether.DEPTH_FLOOR_LAYERS to reflect the mod's floor Y value, and call
+-- shift_existing_biomes() with DEPTH_FLOOR_LAYERS as the floor_y argument.
+nether.DEPTH_FLOOR_LAYERS = nether.DEPTH_FLOOR
 
 -- A debug-print function that understands vectors etc. and does not
 -- evaluate when debugging is turned off.
@@ -115,6 +134,8 @@ end
 -- Load files
 dofile(nether.path .. "/portal_api.lua")
 dofile(nether.path .. "/nodes.lua")
+dofile(nether.path .. "/tools.lua")
+dofile(nether.path .. "/crafts.lua")
 if nether.NETHER_REALM_ENABLED then
 	if nether.useBiomes then
 		dofile(nether.path .. "/mapgen.lua")
@@ -147,7 +168,7 @@ This opens to a truly hellish place, though for small mercies the air there is s
 The expedition parties have found no diamonds or gold, and after an experienced search party failed to return from the trail of a missing expedition party, I must conclude this is a dangerous place.]], 10 * nether.FASTTRAVEL_FACTOR),
 
 		is_within_realm = function(pos) -- return true if pos is inside the Nether
-			return pos.y < nether.DEPTH_CEILING
+			return pos.y < nether.DEPTH_CEILING and pos.y > nether.DEPTH_FLOOR
 		end,
 
 		find_realm_anchorPos = function(surface_anchorPos, player_name)
@@ -155,7 +176,7 @@ The expedition parties have found no diamonds or gold, and after an experienced
 			local destination_pos = vector.divide(surface_anchorPos, nether.FASTTRAVEL_FACTOR)
 			destination_pos.x = math.floor(0.5 + destination_pos.x) -- round to int
 			destination_pos.z = math.floor(0.5 + destination_pos.z) -- round to int
-			destination_pos.y = nether.DEPTH_CEILING - 1000 -- temp value so find_nearest_working_portal() returns nether portals
+			destination_pos.y = nether.DEPTH_CEILING - 1 -- temp value so find_nearest_working_portal() returns nether portals
 
 			-- a y_factor of 0 makes the search ignore the altitude of the portals (as long as they are in the Nether)
 			local existing_portal_location, existing_portal_orientation =
@@ -180,7 +201,7 @@ The expedition parties have found no diamonds or gold, and after an experienced
 			local destination_pos = vector.multiply(realm_anchorPos, nether.FASTTRAVEL_FACTOR)
 			destination_pos.x = math.min(30900, math.max(-30900, destination_pos.x)) -- clip to world boundary
 			destination_pos.z = math.min(30900, math.max(-30900, destination_pos.z)) -- clip to world boundary
-			destination_pos.y = 0 -- temp value so find_nearest_working_portal() doesn't return nether portals
+			destination_pos.y = nether.DEPTH_CEILING + 1 -- temp value so find_nearest_working_portal() doesn't return nether portals
 
 			-- a y_factor of 0 makes the search ignore the altitude of the portals (as long as they are outside the Nether)
 			local existing_portal_location, existing_portal_orientation =
@@ -225,4 +246,103 @@ The expedition parties have found no diamonds or gold, and after an experienced
 		end
 
 	})
-end
+
+
+	-- Set appropriate nether distance-fog if climate_api is available
+	--
+	-- Delegating to a mod like climate_api means nether won't unexpectedly stomp on the sky of
+	-- any other mod.
+	-- Skylayer is another mod which can perform this role, and skylayer support could be added
+	-- here as well. However skylayer doesn't provide a position-based method of specifying sky
+	-- colours out-of-the-box, so the nether mod will have to monitor when players enter and
+	-- leave the nether.
+	if minetest.get_modpath("climate_api") and minetest.global_exists("climate_api") and climate_api.register_weather ~= nil then
+
+		climate_api.register_influence(
+			"nether_biome",
+			function(pos)
+				local result = "surface"
+
+				if pos.y <= nether.DEPTH_CEILING and pos.y >= nether.DEPTH_FLOOR then
+					result = "nether"
+
+					-- since mapgen_nobiomes.lua has no regions it doesn't implement get_region(),
+					-- so only use get_region() if it exists
+					if nether.mapgen.get_region ~= nil then
+						-- the biomes-based mapgen supports 2 extra regions
+						local regions = nether.mapgen.RegionEnum
+						local region  = nether.mapgen.get_region(pos)
+						if region == regions.CENTER or region == regions.CENTERSHELL then
+							result = "mantle"
+						elseif region == regions.NEGATIVE or region == regions.NEGATIVESHELL then
+							result = "geode"
+						end
+					end
+				end
+
+				return result
+			end
+		)
+
+		-- using sky type "plain" unfortunately means we don't get smooth fading transitions when
+		-- the color of the sky changes, but it seems to be the only way to obtain a sky colour
+		-- which doesn't brighten during the daytime.
+		local undergroundSky = {
+			sky_data = {
+				base_color = nil,
+				type = "plain",
+				textures = nil,
+				clouds = false,
+			},
+			sun_data = {
+				visible = false,
+				sunrise_visible = false
+			},
+			moon_data = {
+				visible = false
+			},
+			star_data = {
+				visible = false
+			}
+		}
+
+		local netherSky, mantleSky, geodeSky = table.copy(undergroundSky), table.copy(undergroundSky), table.copy(undergroundSky)
+		netherSky.sky_data.base_color = nether.fogColor.netherCaverns
+		mantleSky.sky_data.base_color = nether.fogColor.mantle
+		geodeSky.sky_data.base_color  = nether.fogColor.geodes
+
+		climate_api.register_weather(
+			"nether:nether",
+			{ nether_biome = "nether" },
+			{ ["climate_api:skybox"] = netherSky }
+		)
+
+		climate_api.register_weather(
+			"nether:mantle",
+			{ nether_biome = "mantle" },
+			{ ["climate_api:skybox"] = mantleSky }
+		)
+
+		climate_api.register_weather(
+			"nether:geode",
+			{ nether_biome = "geode" },
+			{ ["climate_api:skybox"] = geodeSky }
+		)
+	end
+
+end -- end of "if nether.NETHER_REALM_ENABLED..."
+
+
+-- Play bubbling lava sounds if player killed by lava
+minetest.register_on_dieplayer(
+	function(player, reason)
+		if reason.node ~= nil and minetest.get_node_group(reason.node, "lava") > 0 or reason.node == "nether:lava_crust" then
+			minetest.sound_play(
+				"nether_lava_bubble",
+				-- this sample was encoded at 3x speed to reduce .ogg file size
+				-- at the expense of higher frequencies, so pitch it down ~3x
+				{to_player = player:get_player_name(), pitch = 0.3, gain = 0.8}
+			)
+		end
+	end
+)

locale/nether.fr.tr

@@ -0,0 +1,115 @@
+# textdomain: nether
+
+# Translation FR by Louis Royer
+
+
+### init.lua ###
+
+Construction requires 14 blocks of obsidian, which we found deep underground where water had solidified molten rock. The finished frame is four blocks wide, five blocks high, and stands vertically, like a doorway.@n@nThis opens to a truly hellish place, though for small mercies the air there is still breathable. There is an intriguing dimensional mismatch happening between this realm and ours, as after opening the second portal into it we observed that 10 strides taken in the Nether appear to be an equivalent of @1 in the natural world.@n@nThe expedition parties have found no diamonds or gold, and after an experienced search party failed to return from the trail of a missing expedition party, I must conclude this is a dangerous place.=Cette construction nécessite 14 blocs d’obsidienne, qui peut être trouvée profondément sous terre, là où l’eau a solidifié de la roche fondue. Une fois terminé, le cadre fait quatre blocs de large, cinq blocs de haut, et se tient verticalement comme une porte.@n@nElle ouvre sur un lieu vraiment infernal, mais on peut s’estimer heureux que l’air y soit quand même respirable. Il y a un décalage dimensionnel intrigant entre ce monde et le nôtre, car après avoir ouvert un deuxième portail, nous avons observé que 10 pas effectués dans le Nether semblent être l’équivalent de @1 dans notre monde.@n@nLes membres de l’expédition n’ontr trouvé ni diamants ni or, et après qu’un groupe de recheche expérimenté n’ait pas réussi à retrouver la piste d’un membre de l’expédition disparu, je n’ai d’autre choix que de conclure que cet endroit est trop dangereux pour nous.
+
+
+### init.lua ###
+### nodes.lua ###
+
+Nether Portal=Portail du Nether
+
+### mapgen_mantle.lua ###
+
+, @1m above lava-sea level=
+, @1m below lava-sea level=
+, approaching y boundary of Nether=
+@1@2@3@4=
+Center/Mantle, but outside the caverns=
+Center/Mantle, inside cavern=
+Describes which region of the nether the player is in=
+Negative nether=
+Positive nether=
+Shell between negative nether and center region=
+Shell between positive nether and center region=
+The Overworld=
+Unknown player position=
+[Perlin @1] =
+
+### nodes.lua ###
+
+A finely finished block of solid Nether Basalt.=
+A rough cut solid block of Nether Basalt.=
+A thin crust of cooled lava with liquid lava beneath=
+A vent in the earth emitting steam and gas=
+Can be repurposed to provide puffs of smoke in a chimney=
+Chiselled Basalt=
+
+Columns of dark basalt found only in magma oceans deep within the Nether.=
+
+Compressed Netherbrick=
+Cracked Nether Brick=
+Deep Glowstone=
+Deep Netherrack=
+Fumarolic Chimney=
+Fumarolic Chimney Corner=
+Fumarolic Chimney Slab=
+Glowstone=Pierre lumineuse
+Hewn Basalt=
+Inner Nether Stair=Escalier intérieur du Nether
+Lava Crust=
+
+Lava crust is strong enough to walk on, but still hot enough to inflict burns.=
+
+Nether Basalt=
+Nether Brick=Brique du Nether
+Nether Brick Fence=Barrière en briques du Nether
+Nether Slab=Dalle du Nether
+Nether Stair=Escalier du Nether
+Netherrack=Roche du Nether
+Netherrack from deep in the mantle=
+Netherrack stair=
+Nethersand=Sable du Nether
+Outer Nether Stair=Escalier extérieur du Nether
+Portal=
+
+### portal_api.lua ###
+
+@n@nThe key to opening such a doorway is to strike the frame with a @1, at which point the very air inside begins to crackle and glow.=@n@nLa méthode pour ouvrir une telle porte est de frapper son cadre avec un @1, jusqu’à ce que tout l’air à l’intérieur commence à crépiter et briller.
+
+A definitive guide to Rifts and Portals=Un guide détaillé des failles et des portails
+
+A guidebook for how to build portals to other realms. It can sometimes be found in dungeon chests, however a copy of this book is not needed as its contents are included in this Encyclopedia.=Un guide sur comment construire des portails vers d’autres mondes. Il peut parfois être trouvé dans des coffres de dongeons, cependant la copie de ce livre n’est pas nécessaire puisque son contenu est inclus dans l’encyclopédie.
+
+Book of Portals=Livre des portails
+Building Portals=Construire des portails
+
+In all my travels, and time spent in the Great Libraries, I have encountered no shortage of legends surrounding preternatural doorways said to open into other worlds, yet only @1 can I confirm as being more than merely stories.=Après tous mes voyages, et le temps passé dans les Grandes Bibliothèques, je ne manque pas de légendes sur les portes surnaturelles qui, dit-on s’ouvrent vers d’autres mondes, mais seul @1 peut confirmer que ce sont plus que de simples histoires.
+
+In all my travels, and time spent in the Great Libraries, I have encountered no shortage of legends surrounding preternatural doorways said to open into other worlds, yet only one can I confirm as being more than merely a story.=Après tous mes voyages, et le temps passé dans les Grandes Bibliothèques, je ne manque pas de légendes sur les portes surnaturelles qui, dit-on s’ouvrent vers d’autres mondes, mais seul une personne peut confirmer que ce sont plus que de simples histoires.
+
+Mysterious forces prevented you from opening that portal. Please try another location=
+
+Portal wormhole=Vortex du portail
+
+Portals to other realms can be opened by building a frame in the right shape with the right blocks, then using an item to activate it. A local copy of the guidebook to portals is published below.@n---@n@n=Les portails vers d’autres mondes peuvent être ouvert en construisant un cadre de la bonne forme avec les bons blocs, puis en utilisant un objet pour l’activer. Une copie du guide des portails est ci-dessous.@n---@n@n
+
+Refer: "Help" > "Basics" > "Building Portals"=Voir : Aide > Bases > Construire des portails
+Untitled portal=Portail sans nom
+We know almost nothing about this portal=Nous ne savons presque rien sur les portails
+
+### portal_examples.lua ###
+
+Floatlands Portal=Portail du monde flottant
+
+Requiring 16 blocks of tin and constructed in a circular fashion, a finished frame is seven blocks wide, seven blocks high, and stands vertically like a doorway.@n@nThese travel a distance along the ground, and even when constructed deep underground will link back up to the surface. They appear to favor a strange direction, with the exit portal linking back only for as long as the portal stays open — attempting to reopen a portal from the exit doorway leads to a new destination along this favored direction. It has stymied our ability to study the behavior of these portals because without constructing dual portals and keeping both open it's hard to step through more than one and still be able to return home.@n@nDue to such difficulties, we never learned what determines the direction and distance where the matching twin portal will appear, and I have lost my friend and protégé. In cavalier youth and with little more than a rucksack, Coudreau has decided to follow the chain as far as it goes, and has not been seen since. Coudreau believes it works in epicycles, but I am not convinced. Still, I cling to the hope that one day the portal will open and Coudreau will step out from whichever place leads to this one, perhaps with an epic tale to tell.=Nécessite 16 blocs d’étain placés de manière circulaire, le cadre final fait sept blocs de large, sept blocs de haut, et se tient verticalement comme une porte.@n@nIls permettent de voyager une distance sous le sol et se relieent à la surface même s’ils sont construits profondément sous terre. Ils ont l’air de préférer une direction étrange, avec le portail de sortie ne se reliant au portail d’entrée que tant qu’ils restent tous deux ouverts – tenter de réouvrir le portail de sortie mènera à une nouvelle destination dans cette direction privilégiée.Cela a entravé notre capacité à étudier le comportement de ces portails, car sans la construction de doubles portails et en gardant les deux ouverts, il est difficile d'en traverser plus d'un et de pouvoir rentrer chez soi.@n@nEn raison de ces difficultés, nous n'avons jamais appris ce qui détermine la direction et la distance à laquelle le portail jumeau correspondant apparaîtra, et j’ai perdu mon ami et mon protégé. Dans sa jeunesse cavalière et avec à peine plus qu'un sac à dos, Coudreau a décidé de suivre la chaîne jusqu'au bout, et n'a pas été vu depuis. Coudreau croit qu'elle fonctionne sur les épicycles, mais je n'en suis pas convaincu. Je m'accroche néanmoins à l'espoir qu'un jour le portail s'ouvrira et que Coudreau sortira de l'endroit qui mène à celui-ci, peut-être avec un récit épique à raconter.
+
+Requiring 21 blocks of ice, and constructed in the shape of a 3 × 3 platform with walls, or like a bowl. A finished platform is 2 blocks high, and 5 blocks wide at the widest in both directions.@n@nThis portal is different to the others, rather than acting akin to a doorway it appears to the eye more like a small pool of water which can be stepped into. Upon setting foot in the portal we found ourselves at a tremendous altitude.@1=Nécessite 21 blocs de glace placés pour former une plateforme de 3 × 3 avec des murs, ou comme un bol. La plateforme finale fait 2 blocs de haut, et 5 blocs de large à sa largeur maximale dans les deux directions.@n@nCe portail est différent des autres, au lieu de ressembler à une porte, il ressemble plus à un petit bassin d’eau dans lequel on peut entrer. En mettant les pieds dans le portail, nous nous sommes retrouvés à une altitude énorme.@1
+
+Surface Portal=Portail de surface
+
+There is a floating land of hills and forests up there, over the edges of which is a perilous drop all the way back down to sea level. We have not found how far these pristine lands extend. I have half a mind to retire there one day.=Il y a là un monde flottant remplis de collines et de forêts, sur les bords duquel se trouve une chute périlleuse jusqu'au niveau de la mer. Nous n'avons pas encore trouvé jusqu'où s'étendent ces terres vierges. J'ai à moitié envie de m'y retirer un jour.
+
+
+### tools.lua ###
+
+Nether Axe=
+Nether Ingot=
+Nether Lump=
+Nether Pickaxe=
+Nether Shovel=
+Nether Sword=

locale/template.txt

@@ -0,0 +1,114 @@
+# textdomain: nether
+
+
+
+### init.lua ###
+
+Construction requires 14 blocks of obsidian, which we found deep underground where water had solidified molten rock. The finished frame is four blocks wide, five blocks high, and stands vertically, like a doorway.@n@nThis opens to a truly hellish place, though for small mercies the air there is still breathable. There is an intriguing dimensional mismatch happening between this realm and ours, as after opening the second portal into it we observed that 10 strides taken in the Nether appear to be an equivalent of @1 in the natural world.@n@nThe expedition parties have found no diamonds or gold, and after an experienced search party failed to return from the trail of a missing expedition party, I must conclude this is a dangerous place.=
+
+
+### init.lua ###
+### nodes.lua ###
+
+Nether Portal=
+
+### mapgen_mantle.lua ###
+
+, @1m above lava-sea level=
+, @1m below lava-sea level=
+, approaching y boundary of Nether=
+@1@2@3@4=
+Center/Mantle, but outside the caverns=
+Center/Mantle, inside cavern=
+Describes which region of the nether the player is in=
+Negative nether=
+Positive nether=
+Shell between negative nether and center region=
+Shell between positive nether and center region=
+The Overworld=
+Unknown player position=
+[Perlin @1] =
+
+### nodes.lua ###
+
+A finely finished block of solid Nether Basalt.=
+A rough cut solid block of Nether Basalt.=
+A thin crust of cooled lava with liquid lava beneath=
+A vent in the earth emitting steam and gas=
+Can be repurposed to provide puffs of smoke in a chimney=
+Chiselled Basalt=
+
+Columns of dark basalt found only in magma oceans deep within the Nether.=
+
+Compressed Netherbrick=
+Cracked Nether Brick=
+Deep Glowstone=
+Deep Netherrack=
+Fumarolic Chimney=
+Fumarolic Chimney Corner=
+Fumarolic Chimney Slab=
+Glowstone=
+Hewn Basalt=
+Inner Nether Stair=
+Lava Crust=
+
+Lava crust is strong enough to walk on, but still hot enough to inflict burns.=
+
+Nether Basalt=
+Nether Brick=
+Nether Brick Fence=
+Nether Slab=
+Nether Stair=
+Netherrack=
+Netherrack from deep in the mantle=
+Netherrack stair=
+Nethersand=
+Outer Nether Stair=
+Portal=
+
+### portal_api.lua ###
+
+@n@nThe key to opening such a doorway is to strike the frame with a @1, at which point the very air inside begins to crackle and glow.=
+
+A definitive guide to Rifts and Portals=
+
+A guidebook for how to build portals to other realms. It can sometimes be found in dungeon chests, however a copy of this book is not needed as its contents are included in this Encyclopedia.=
+
+Book of Portals=
+Building Portals=
+
+In all my travels, and time spent in the Great Libraries, I have encountered no shortage of legends surrounding preternatural doorways said to open into other worlds, yet only @1 can I confirm as being more than merely stories.=
+
+In all my travels, and time spent in the Great Libraries, I have encountered no shortage of legends surrounding preternatural doorways said to open into other worlds, yet only one can I confirm as being more than merely a story.=
+
+Mysterious forces prevented you from opening that portal. Please try another location=
+
+Portal wormhole=
+
+Portals to other realms can be opened by building a frame in the right shape with the right blocks, then using an item to activate it. A local copy of the guidebook to portals is published below.@n---@n@n=
+
+Refer: "Help" > "Basics" > "Building Portals"=
+Untitled portal=
+We know almost nothing about this portal=
+
+### portal_examples.lua ###
+
+Floatlands Portal=
+
+Requiring 16 blocks of tin and constructed in a circular fashion, a finished frame is seven blocks wide, seven blocks high, and stands vertically like a doorway.@n@nThese travel a distance along the ground, and even when constructed deep underground will link back up to the surface. They appear to favor a strange direction, with the exit portal linking back only for as long as the portal stays open — attempting to reopen a portal from the exit doorway leads to a new destination along this favored direction. It has stymied our ability to study the behavior of these portals because without constructing dual portals and keeping both open it's hard to step through more than one and still be able to return home.@n@nDue to such difficulties, we never learned what determines the direction and distance where the matching twin portal will appear, and I have lost my friend and protégé. In cavalier youth and with little more than a rucksack, Coudreau has decided to follow the chain as far as it goes, and has not been seen since. Coudreau believes it works in epicycles, but I am not convinced. Still, I cling to the hope that one day the portal will open and Coudreau will step out from whichever place leads to this one, perhaps with an epic tale to tell.=
+
+Requiring 21 blocks of ice, and constructed in the shape of a 3 × 3 platform with walls, or like a bowl. A finished platform is 2 blocks high, and 5 blocks wide at the widest in both directions.@n@nThis portal is different to the others, rather than acting akin to a doorway it appears to the eye more like a small pool of water which can be stepped into. Upon setting foot in the portal we found ourselves at a tremendous altitude.@1=
+
+Surface Portal=
+
+There is a floating land of hills and forests up there, over the edges of which is a perilous drop all the way back down to sea level. We have not found how far these pristine lands extend. I have half a mind to retire there one day.=
+
+
+### tools.lua ###
+
+Nether Axe=
+Nether Ingot=
+Nether Lump=
+Nether Pickaxe=
+Nether Shovel=
+Nether Sword=

mapgen.lua

@@ -2,6 +2,12 @@
 
   Nether mod for minetest
 
+  "mapgen.lua" is the modern biomes-based Nether mapgen, which
+    requires Minetest v5.1 or greater
+  "mapgen_nobiomes.lua" is the legacy version of the mapgen, only used
+    in older versions of Minetest or in v6 worlds.
+
+
   Copyright (C) 2013 PilzAdam
 
   Permission to use, copy, modify, and/or distribute this software for
@@ -27,10 +33,31 @@ local NETHER_FLOOR   = nether.DEPTH_FLOOR
 local TCAVE = 0.6
 local BLEND = 128
 
+-- parameters for central region
+local REGION_BUFFER_THICKNESS   = 0.2
+local CENTER_REGION_LIMIT       = TCAVE - REGION_BUFFER_THICKNESS -- Netherrack gives way to Deep-Netherrack here
+local CENTER_CAVERN_LIMIT       = CENTER_REGION_LIMIT - 0.1       -- Deep-Netherrack gives way to air here
+local SURFACE_CRUST_LIMIT       = CENTER_CAVERN_LIMIT * 0.25      -- Crusted-lava at the surface of the lava ocean gives way to liquid lava here
+local CRUST_LIMIT               = CENTER_CAVERN_LIMIT * 0.85      -- Crusted-lava under the surface of the lava ocean gives way to liquid lava here
+local BASALT_COLUMN_UPPER_LIMIT = CENTER_CAVERN_LIMIT * 0.9       -- Basalt columns may appear between these upper and lower limits
+local BASALT_COLUMN_LOWER_LIMIT = CENTER_CAVERN_LIMIT * 0.25      -- This value is close to SURFACE_CRUST_LIMIT so basalt columns give way to "flowing" lava rivers
 
--- Stuff
 
-local math_max, math_min = math.max, math.min -- avoid needing table lookups each time a common math function is invoked
+-- Shared Nether mapgen namespace
+-- For mapgen files to share functions and constants
+local mapgen = nether.mapgen
+
+mapgen.TCAVE                     = TCAVE                     -- const needed in mapgen_mantle.lua
+mapgen.BLEND                     = BLEND                     -- const needed in mapgen_mantle.lua
+mapgen.CENTER_REGION_LIMIT       = CENTER_REGION_LIMIT       -- const needed in mapgen_mantle.lua
+mapgen.CENTER_CAVERN_LIMIT       = CENTER_CAVERN_LIMIT       -- const needed in mapgen_mantle.lua
+mapgen.BASALT_COLUMN_UPPER_LIMIT = BASALT_COLUMN_UPPER_LIMIT -- const needed in mapgen_mantle.lua
+mapgen.BASALT_COLUMN_LOWER_LIMIT = BASALT_COLUMN_LOWER_LIMIT -- const needed in mapgen_mantle.lua
+
+mapgen.ore_ceiling = NETHER_CEILING - BLEND -- leave a solid 128 node cap of netherrack before introducing ores
+mapgen.ore_floor   = NETHER_FLOOR   + BLEND
+
+local debugf = nether.debug
 
 if minetest.read_schematic == nil then
 	-- Using biomes to create the Nether requires the ability for biomes to set "node_cave_liquid = air".
@@ -41,7 +68,21 @@ if minetest.read_schematic == nil then
 	error("This " .. nether.modname .. " mapgen requires Minetest v5.1 or greater, use mapgen_nobiomes.lua instead.", 0)
 end
 
-local function override_underground_biomes()
+-- Load specialty helper functions
+dofile(nether.path .. "/mapgen_dungeons.lua")
+dofile(nether.path .. "/mapgen_mantle.lua")
+
+
+-- Misc math functions
+
+-- avoid needing table lookups each time a common math function is invoked
+local math_max, math_min, math_abs, math_floor = math.max, math.min, math.abs, math.floor
+
+
+-- Inject nether_caverns biome
+
+-- Move any existing biomes out of the y-range specified by 'floor_y' and 'ceiling_y'
+mapgen.shift_existing_biomes = function(floor_y, ceiling_y)
 	-- https://forum.minetest.net/viewtopic.php?p=257522#p257522
 	-- Q: Is there a way to override an already-registered biome so I can get it out of the
 	--    way of my own underground biomes without disturbing the other biomes registered by
@@ -68,7 +109,7 @@ local function override_underground_biomes()
 	end
 	for old_ore_key, old_ore_def in pairs(minetest.registered_ores) do
 		registered_ores_copy[old_ore_key] = old_ore_def
-	 end
+	end
 
 	-- clear biomes, decorations, and ores
 	minetest.clear_registered_decorations()
@@ -77,23 +118,36 @@ local function override_underground_biomes()
 
 	-- Restore biomes, adjusted to not overlap the Nether
 	for biome_key, new_biome_def in pairs(registered_biomes_copy) do
-		local biome_y_max, biome_y_min = tonumber(new_biome_def.y_max), tonumber(new_biome_def.y_min)
+		-- follow similar min_pos/max_pos processing logic as read_biome_def() in l_mapgen.cpp
+		local biome_y_max, biome_y_min = 31000, -31000
+		if type(new_biome_def.min_pos) == 'table' and type(new_biome_def.min_pos.y) == 'number' then biome_y_min = new_biome_def.min_pos.y end
+		if type(new_biome_def.max_pos) == 'table' and type(new_biome_def.max_pos.y) == 'number' then biome_y_max = new_biome_def.max_pos.y end
+		if type(new_biome_def.y_min) == 'number' then biome_y_min = new_biome_def.y_min end
+		if type(new_biome_def.y_max) == 'number' then biome_y_max = new_biome_def.y_max end
 
-		if biome_y_max > NETHER_FLOOR and biome_y_min < NETHER_CEILING then
+		if biome_y_max > floor_y and biome_y_min < ceiling_y then
 			-- This biome occupies some or all of the depth of the Nether, shift/crop it.
-			local spaceOccupiedAbove = biome_y_max - NETHER_CEILING
-			local spaceOccupiedBelow = NETHER_FLOOR - biome_y_min
+			local new_y_min, new_y_max
+			local spaceOccupiedAbove = biome_y_max - ceiling_y
+			local spaceOccupiedBelow = floor_y - biome_y_min
 			if spaceOccupiedAbove >= spaceOccupiedBelow or biome_y_min <= -30000 then
 				-- place the biome above the Nether
 				-- We also shift biomes which extend to the bottom of the map above the Nether, since they
 				-- likely only extend that deep as a catch-all, and probably have a role nearer the surface.
-				new_biome_def.y_min = NETHER_CEILING + 1
-				new_biome_def.y_max = math_max(biome_y_max, NETHER_CEILING + 2)
+				new_y_min = ceiling_y + 1
+				new_y_max = math_max(biome_y_max, ceiling_y + 2)
 			else
 				-- shift the biome to below the Nether
-				new_biome_def.y_max = NETHER_FLOOR - 1
-				new_biome_def.y_min = math_min(biome_y_min, NETHER_CEILING - 2)
+				new_y_max = floor_y - 1
+				new_y_min = math_min(biome_y_min, floor_y - 2)
 			end
+
+			debugf("Moving biome \"%s\" from %s..%s to %s..%s", new_biome_def.name, new_biome_def.y_min, new_biome_def.y_max, new_y_min, new_y_max)
+
+			if type(new_biome_def.min_pos) == 'table' and type(new_biome_def.min_pos.y) == 'number' then new_biome_def.min_pos.y = new_y_min end
+			if type(new_biome_def.max_pos) == 'table' and type(new_biome_def.max_pos.y) == 'number' then new_biome_def.max_pos.y = new_y_max end
+			new_biome_def.y_min = new_y_min -- Ensure the new heights are saved, even if original biome never specified one
+			new_biome_def.y_max = new_y_max
 		end
 		minetest.register_biome(new_biome_def)
 	end
@@ -109,7 +163,7 @@ local function override_underground_biomes()
  end
 
 -- Shift any overlapping biomes out of the way before we create the Nether biomes
-override_underground_biomes()
+mapgen.shift_existing_biomes(NETHER_FLOOR, NETHER_CEILING)
 
 -- nether:native_mapgen is used to prevent ores and decorations being generated according
 -- to landforms created by the native mapgen.
@@ -121,9 +175,9 @@ minetest.register_node("nether:native_mapgen", {})
 minetest.register_biome({
 	name = "nether_caverns",
 	node_stone  = "nether:native_mapgen", -- nether:native_mapgen is used here to prevent the native mapgen from placing ores and decorations.
-	node_filler = "nether:native_mapgen", -- The lua on_generate will transform nether:rack_native into nether:rack then decorate and add ores.
+	node_filler = "nether:native_mapgen", -- The lua on_generate will transform nether:native_mapgen into nether:rack then decorate and add ores.
 	node_dungeon = "nether:brick",
-	--node_dungeon_alt = "default:mossycobble",
+	node_dungeon_alt = "nether:brick_cracked",
 	node_dungeon_stair = "stairs:stair_nether_brick",
 	-- Setting node_cave_liquid to "air" avoids the need to filter lava and water out of the mapchunk and
 	-- surrounding shell (overdraw nodes beyond the mapchunk).
@@ -152,19 +206,30 @@ minetest.register_ore({
 	clust_scarcity = 11 * 11 * 11,
 	clust_num_ores = 3,
 	clust_size     = 2,
-	y_max = NETHER_CEILING,
-	y_min = NETHER_FLOOR,
+	y_max = mapgen.ore_ceiling,
+	y_min = mapgen.ore_floor
+})
+
+minetest.register_ore({
+	ore_type       = "scatter",
+	ore            = "nether:lava_crust", -- crusted lava replaces scattered glowstone in the mantle
+	wherein        = "nether:rack_deep",
+	clust_scarcity = 16 * 16 * 16,
+	clust_num_ores = 4,
+	clust_size     = 2,
+	y_max = mapgen.ore_ceiling,
+	y_min = mapgen.ore_floor
 })
 
 minetest.register_ore({
 	ore_type       = "scatter",
 	ore            = "default:lava_source",
-	wherein        = "nether:rack",
+	wherein        = {"nether:rack", "nether:rack_deep"},
 	clust_scarcity = 36 * 36 * 36,
 	clust_num_ores = 4,
 	clust_size     = 2,
-	y_max = NETHER_CEILING,
-	y_min = NETHER_FLOOR,
+	y_max = mapgen.ore_ceiling,
+	y_min = mapgen.ore_floor
 })
 
 minetest.register_ore({
@@ -173,8 +238,8 @@ minetest.register_ore({
 	wherein         = "nether:rack",
 	clust_scarcity  = 14 * 14 * 14,
 	clust_size      = 8,
-	y_max = NETHER_CEILING,
-	y_min = NETHER_FLOOR
+	y_max = mapgen.ore_ceiling,
+	y_min = mapgen.ore_floor
 })
 
 
@@ -182,7 +247,7 @@ minetest.register_ore({
 
 -- 3D noise
 
-local np_cave = {
+mapgen.np_cave = {
 	offset = 0,
 	scale = 1,
 	spread = {x = 384, y = 128, z = 384}, -- squashed 3:1
@@ -193,210 +258,74 @@ local np_cave = {
 	--flags = ""
 }
 
+local cavePointPerlin = nil
+
+mapgen.get_cave_point_perlin = function()
+	cavePointPerlin = cavePointPerlin or minetest.get_perlin(mapgen.np_cave)
+	return cavePointPerlin
+end
+
+mapgen.get_cave_perlin_at = function(pos)
+	cavePointPerlin = cavePointPerlin or minetest.get_perlin(mapgen.np_cave)
+	return cavePointPerlin:get_3d(pos)
+end
+
+
 -- Buffers and objects we shouldn't recreate every on_generate
 
 local nobj_cave = nil
 local nbuf_cave = {}
 local dbuf = {}
 
-local yblmin = NETHER_FLOOR   + BLEND * 2
-local yblmax = NETHER_CEILING - BLEND * 2
 
 -- Content ids
 
 local c_air              = minetest.get_content_id("air")
 local c_netherrack       = minetest.get_content_id("nether:rack")
-local c_netherbrick      = minetest.get_content_id("nether:brick")
-local c_netherbrick_slab = minetest.get_content_id("stairs:slab_nether_brick")
-local c_netherfence      = minetest.get_content_id("nether:fence_nether_brick")
-local c_glowstone        = minetest.get_content_id("nether:glowstone")
-local c_lava_source      = minetest.get_content_id("default:lava_source")
+local c_netherrack_deep  = minetest.get_content_id("nether:rack_deep")
+local c_lavasea_source   = minetest.get_content_id("nether:lava_source") -- same as lava but with staggered animation to look better as an ocean
+local c_lava_crust       = minetest.get_content_id("nether:lava_crust")
 local c_native_mapgen    = minetest.get_content_id("nether:native_mapgen")
 
 
--- Dungeon excavation functions
 
-function build_dungeon_room_list(data, area)
+local yblmin = NETHER_FLOOR   + BLEND * 2
+local yblmax = NETHER_CEILING - BLEND * 2
+-- At both the top and bottom of the Nether, as set by NETHER_CEILING and NETHER_FLOOR,
+-- there is a 128 deep cap of solid netherrack, followed by a 128-deep blending zone
+-- where Nether caverns may start to appear.
+-- The solid zones and blending zones are achieved by adjusting the np_cave noise to be
+-- outside the range where caverns form, this function returns that adjustment.
+--
+-- Returns two values: the noise limit adjustment for nether caverns, and the
+-- noise limit adjustment for the central region / mantle caverns
+mapgen.get_mapgenblend_adjustments = function(y)
 
-	local result = {}
+	-- floorAndCeilingBlend will normally be 0, but shifts toward 1 in the
+	-- blending zone, and goes higher than 1 in the solid zone between the
+	-- blending zone and the end of the nether.
+	local floorAndCeilingBlend = 0
+	if y > yblmax then floorAndCeilingBlend = ((y - yblmax) / BLEND) ^ 2 end
+	if y < yblmin then floorAndCeilingBlend = ((yblmin - y) / BLEND) ^ 2 end
 
-	-- Unfortunately gennotify only returns dungeon rooms, not corridors.
-	-- We don't need to check for temples because only dungeons are generated in biomes
-	-- that define their own dungeon nodes.
-	local gennotify = minetest.get_mapgen_object("gennotify")
-	local roomLocations = gennotify["dungeon"] or {}
+	-- the nether caverns exist when np_cave noise is greater than TCAVE, so
+	-- to fade out the nether caverns, adjust TCAVE upward.
+	local tcave_adj               = floorAndCeilingBlend
 
-	-- Excavation should still know to stop if a cave or corridor has removed the dungeon wall.
-	-- See MapgenBasic::generateDungeons in mapgen.cpp for max room sizes.
-	local maxRoomSize = 18
-	local maxRoomRadius = math.ceil(maxRoomSize / 2)
+	-- the central regions exists when np_cave noise is below CENTER_REGION_LIMIT,
+	-- so to fade out the mantle caverns adjust CENTER_REGION_LIMIT downward.
+	local centerRegionLimit_adj = -(CENTER_REGION_LIMIT * floorAndCeilingBlend)
 
-	local xStride, yStride, zStride = 1, area.ystride, area.zstride
-	local minEdge, maxEdge = area.MinEdge, area.MaxEdge
-
-	for _, roomPos in ipairs(roomLocations) do
-
-		if area:containsp(roomPos) then -- this safety check does not appear to be necessary, but lets make it explicit
-
-			local room_vi = area:indexp(roomPos)
-			--data[room_vi] = minetest.get_content_id("default:torch") -- debug
-
-			local startPos = vector.new(roomPos)
-			if roomPos.y + 1 <= maxEdge.y and data[room_vi + yStride] == c_air then
-				-- The roomPos coords given by gennotify are at floor level, but whenever possible we
-				-- want to be performing searches a node higher than floor level to avoids dungeon chests.
-				startPos.y = startPos.y + 1
-				room_vi = area:indexp(startPos)
-			end
-
-			local bound_min_x = math_max(minEdge.x, roomPos.x - maxRoomRadius)
-			local bound_min_y = math_max(minEdge.y, roomPos.y - 1) -- room coords given by gennotify are on the floor
-			local bound_min_z = math_max(minEdge.z, roomPos.z - maxRoomRadius)
-
-			local bound_max_x = math_min(maxEdge.x, roomPos.x + maxRoomRadius)
-			local bound_max_y = math_min(maxEdge.y, roomPos.y + maxRoomSize) -- room coords given by gennotify are on the floor
-			local bound_max_z = math_min(maxEdge.z, roomPos.z + maxRoomRadius)
-
-			local room_min = vector.new(startPos)
-			local room_max = vector.new(startPos)
-
-			local vi = room_vi
-			while room_max.y < bound_max_y and data[vi + yStride] == c_air do
-				room_max.y = room_max.y + 1
-				vi = vi + yStride
-			end
-
-			vi = room_vi
-			while room_min.y > bound_min_y and data[vi - yStride] == c_air do
-				room_min.y = room_min.y - 1
-				vi = vi - yStride
-			end
-
-			vi = room_vi
-			while room_max.z < bound_max_z and data[vi + zStride] == c_air do
-				room_max.z = room_max.z + 1
-				vi = vi + zStride
-			end
-
-			vi = room_vi
-			while room_min.z > bound_min_z and data[vi - zStride] == c_air do
-				room_min.z = room_min.z - 1
-				vi = vi - zStride
-			end
-
-			vi = room_vi
-			while room_max.x < bound_max_x and data[vi + xStride] == c_air do
-				room_max.x = room_max.x + 1
-				vi = vi + xStride
-			end
-
-			vi = room_vi
-			while room_min.x > bound_min_x and data[vi - xStride] == c_air do
-				room_min.x = room_min.x - 1
-				vi = vi - xStride
-			end
-
-			local roomInfo = vector.new(roomPos)
-			roomInfo.minp = room_min
-			roomInfo.maxp = room_max
-			result[#result + 1] = roomInfo
-		end
-	end
-
-	return result;
+	return tcave_adj, centerRegionLimit_adj
 end
 
--- Only partially excavates dungeons, the rest is left as an exercise for the player ;)
--- (Corridors and the parts of rooms which extend beyond the emerge boundary will remain filled)
-function excavate_dungeons(data, area, rooms)
-
-	-- any air from the native mapgen has been replaced by netherrack, but
-	-- we don't want this inside dungeons, so fill dungeon rooms with air
-	for _, roomInfo in ipairs(rooms) do
-
-		local room_min = roomInfo.minp
-		local room_max = roomInfo.maxp
-
-		for z = room_min.z, room_max.z do
-			for y = room_min.y, room_max.y do
-				local vi = area:index(room_min.x, y, z)
-				for x = room_min.x, room_max.x do
-					if data[vi] == c_netherrack then data[vi] = c_air end
-					vi = vi + 1
-				end
-			end
-		end
-	end
-end
-
--- Since we already know where all the rooms and their walls are, and have all the nodes stored
--- in a voxelmanip already, we may as well add a little Nether flair to the dungeons found here.
-function decorate_dungeons(data, area, rooms)
-
-	local xStride, yStride, zStride = 1, area.ystride, area.zstride
-	local minEdge, maxEdge = area.MinEdge, area.MaxEdge
-
-	for _, roomInfo in ipairs(rooms) do
-
-		local room_min, room_max = roomInfo.minp, roomInfo.maxp
-		local room_size = vector.distance(room_min, room_max)
-
-		if room_size > 10 then
-			local room_seed = roomInfo.x + 3 * roomInfo.z + 13 * roomInfo.y
-			local window_y  = roomInfo.y + math_min(2, room_max.y - roomInfo.y - 1)
-
-			if room_seed % 3 == 0 and room_max.y < maxEdge.y then
-				-- Glowstone chandelier
-				local vi = area:index(roomInfo.x, room_max.y + 1, roomInfo.z)
-				if data[vi] == c_netherbrick then data[vi] = c_glowstone end
-
-			elseif room_seed % 4 == 0 and room_min.y > minEdge.y
-				   and room_min.x > minEdge.x and room_max.x < maxEdge.x
-				   and room_min.z > minEdge.z and room_max.z < maxEdge.z then
-				-- lava well (feel free to replace with a fancy schematic)
-				local vi = area:index(roomInfo.x, room_min.y, roomInfo.z)
-				if data[vi - yStride] == c_netherbrick then data[vi - yStride] = c_lava_source end
-				if data[vi - zStride] == c_air then data[vi - zStride] = c_netherbrick_slab end
-				if data[vi + zStride] == c_air then data[vi + zStride] = c_netherbrick_slab end
-				if data[vi - xStride] == c_air then data[vi - xStride] = c_netherbrick_slab end
-				if data[vi + xStride] == c_air then data[vi + xStride] = c_netherbrick_slab end
-			end
-
-			-- Barred windows
-			if room_seed % 7 < 5 and room_max.x - room_min.x >= 4 and room_max.z - room_min.z >= 4
-			   and window_y >= minEdge.y and window_y + 1 <= maxEdge.y
-			   and room_min.x > minEdge.x and room_max.x < maxEdge.x
-			   and room_min.z > minEdge.z and room_max.z < maxEdge.z then
-				--data[area:indexp(roomInfo)] = minetest.get_content_id("default:mese_post_light") -- debug
-
-				-- Until whisper glass is added, every window will be made of netherbrick fence (rather
-				-- than material depending on room_seed)
-				local window_node = c_netherfence
-
-				local vi_min = area:index(room_min.x - 1, window_y, roomInfo.z)
-				local vi_max = area:index(room_max.x + 1, window_y, roomInfo.z)
-				local locations = {-zStride, zStride, -zStride + yStride, zStride + yStride}
-				for _, offset in ipairs(locations) do
-					if data[vi_min + offset] == c_netherbrick then data[vi_min + offset] = window_node end
-					if data[vi_max + offset] == c_netherbrick then data[vi_max + offset] = window_node end
-				end
-				vi_min = area:index(roomInfo.x, window_y, room_min.z - 1)
-				vi_max = area:index(roomInfo.x, window_y, room_max.z + 1)
-				locations = {-xStride, xStride, -xStride + yStride, xStride + yStride}
-				for _, offset in ipairs(locations) do
-					if data[vi_min + offset] == c_netherbrick then data[vi_min + offset] = window_node end
-					if data[vi_max + offset] == c_netherbrick then data[vi_max + offset] = window_node end
-				end
-			end
-
-			-- Weeds on the floor once Nether weeds are added
-		end
-	end
-end
 
 
 -- On-generated function
 
+local tunnelCandidate_count = 0
+local tunnel_count = 0
+local total_chunk_count = 0
 local function on_generated(minp, maxp, seed)
 
 	if minp.y > NETHER_CEILING or maxp.y < NETHER_FLOOR then
@@ -414,49 +343,131 @@ local function on_generated(minp, maxp, seed)
 	local zCaveStride = yCaveStride * yCaveStride
 	local chulens = {x = yCaveStride, y = yCaveStride, z = yCaveStride}
 
-	nobj_cave = nobj_cave or minetest.get_perlin_map(np_cave, chulens)
+	nobj_cave = nobj_cave or minetest.get_perlin_map(mapgen.np_cave, chulens)
 	local nvals_cave = nobj_cave:get_3d_map_flat(minp, nbuf_cave)
 
+	local dungeonRooms = mapgen.build_dungeon_room_list(data, area) -- function from mapgen_dungeons.lua
+	local abs_cave_noise, abs_cave_noise_adjusted
 
-	local dungeonRooms = build_dungeon_room_list(data, area)
+	local contains_nether = false
+	local contains_mantle = false
+	local contains_ocean  = false
 
-	for y = y0, y1 do -- Y loop first to minimise tcave calculations
 
-		local tcave = TCAVE
-		if y > yblmax then tcave = TCAVE + ((y - yblmax) / BLEND) ^ 2 end
-		if y < yblmin then tcave = TCAVE + ((yblmin - y) / BLEND) ^ 2 end
+	for y = y0, y1 do -- Y loop first to minimise tcave & lava-sea calculations
+
+		local sea_level, cavern_limit_distance = mapgen.find_nearest_lava_sealevel(y) -- function from mapgen_mantle.lua
+		local above_lavasea = y > sea_level
+		local below_lavasea = y < sea_level
+
+		local tcave_adj, centerRegionLimit_adj = mapgen.get_mapgenblend_adjustments(y)
+		local tcave   = TCAVE + tcave_adj
+		local tmantle = CENTER_REGION_LIMIT + centerRegionLimit_adj -- cavern_noise_adj already contains central_region_limit_adj, so tmantle is only for comparisons when cavern_noise_adj hasn't been added to the noise value
+
+		 -- cavern_noise_adj gets added to noise value instead of added to the limit np_noise
+		 -- is compared against, so subtract centerRegionLimit_adj instead of adding
+		local cavern_noise_adj =
+			CENTER_REGION_LIMIT * (cavern_limit_distance * cavern_limit_distance * cavern_limit_distance) -
+			centerRegionLimit_adj
 
 		for z = z0, z1 do
 			local vi = area:index(x0, y, z) -- Initial voxelmanip index
 			local ni = (z - z0) * zCaveStride + (y - y0) * yCaveStride + 1
+			local noise2di = 1 + (z - z0) * yCaveStride
 
 			for x = x0, x1 do
 
-				local id = data[vi] -- Existing node
+				local cave_noise = nvals_cave[ni]
 
-				if nvals_cave[ni] > tcave then
+				if cave_noise > tcave then
+					-- Prime region
+					-- This was the only region in initial versions of the Nether mod.
+					-- It is the only region which portals from the surface will open into.
 					data[vi] = c_air
-				elseif id == c_air or id == c_native_mapgen then
-					data[vi] = c_netherrack -- excavate_dungeons() will mostly reverse this inside dungeons
+					contains_nether = true
+
+				elseif -cave_noise > tcave then
+					-- Secondary/spare region
+					-- This secondary region is unused until someone decides to do something cool or novel with it.
+					-- Reaching here would require the player to first find and journey through the central region,
+					-- as it's always separated from the Prime region by the central region.
+
+					data[vi] = c_netherrack -- For now I've just left this region as solid netherrack instead of air.
+
+					-- Only set contains_nether to true here if you want tunnels created between the secondary region
+					-- and the central region.
+					--contains_nether = true
+					--data[vi] = c_air
+				else
+					-- netherrack walls and/or center region/mantle
+					abs_cave_noise = math_abs(cave_noise)
+
+					-- abs_cave_noise_adjusted makes the center region smaller as distance from the lava ocean
+					-- increases, we do this by pretending the abs_cave_noise value is higher.
+					abs_cave_noise_adjusted = abs_cave_noise + cavern_noise_adj
+
+					if abs_cave_noise_adjusted >= CENTER_CAVERN_LIMIT then
+
+						local id = data[vi] -- Check existing node to avoid removing dungeons
+						if id == c_air or id == c_native_mapgen then
+							if abs_cave_noise < tmantle then
+								data[vi] = c_netherrack_deep
+							else
+								-- the shell seperating the mantle from the rest of the nether...
+								data[vi] = c_netherrack -- excavate_dungeons() will mostly reverse this inside dungeons
+							end
+						end
+
+					elseif above_lavasea then
+						data[vi] = c_air
+						contains_mantle = true
+					elseif abs_cave_noise_adjusted < SURFACE_CRUST_LIMIT or (below_lavasea and abs_cave_noise_adjusted < CRUST_LIMIT) then
+						data[vi] = c_lavasea_source
+						contains_ocean = true
+					else
+						data[vi] = c_lava_crust
+						contains_ocean = true
+					end
 				end
 
 				ni = ni + 1
 				vi = vi + 1
+				noise2di = noise2di + 1
 			end
 		end
 	end
 
+	if contains_mantle or contains_ocean then
+		mapgen.add_basalt_columns(data, area, minp, maxp) -- function from mapgen_mantle.lua
+	end
+
+	if contains_nether and contains_mantle then
+		tunnelCandidate_count = tunnelCandidate_count + 1
+		local success = mapgen.excavate_tunnel_to_center_of_the_nether(data, area, nvals_cave, minp, maxp) -- function from mapgen_mantle.lua
+		if success then tunnel_count = tunnel_count + 1 end
+	end
+	total_chunk_count = total_chunk_count + 1
+	if total_chunk_count % 50 == 0 then
+		debugf(
+			"%s of %s chunks contain both nether and lava-sea (%s%%), %s chunks generated a pathway (%s%%)",
+			tunnelCandidate_count,
+			total_chunk_count,
+			math_floor(tunnelCandidate_count * 100 / total_chunk_count),
+			tunnel_count,
+			math_floor(tunnel_count * 100 / total_chunk_count)
+		)
+	end
+
 	-- any air from the native mapgen has been replaced by netherrack, but we
 	-- don't want netherrack inside dungeons, so fill known dungeon rooms with air.
-	excavate_dungeons(data, area, dungeonRooms)
-	decorate_dungeons(data, area, dungeonRooms)
+	mapgen.excavate_dungeons(data, area, dungeonRooms) -- function from mapgen_dungeons.lua
+	mapgen.decorate_dungeons(data, area, dungeonRooms) -- function from mapgen_dungeons.lua
 
 	vm:set_data(data)
 
-	-- avoid generating decorations on the underside of the bottom of the nether
-	if minp.y > NETHER_FLOOR and maxp.y < NETHER_CEILING then minetest.generate_decorations(vm) end
-
 	minetest.generate_ores(vm)
+	minetest.generate_decorations(vm)
+
 	vm:set_lighting({day = 0, night = 0}, minp, maxp)
 	vm:calc_lighting()
 	vm:update_liquids()
@@ -467,7 +478,7 @@ end
 -- use knowledge of the nether mapgen algorithm to return a suitable ground level for placing a portal.
 -- player_name is optional, allowing a player to spawn a remote portal in their own protected areas.
 function nether.find_nether_ground_y(target_x, target_z, start_y, player_name)
-	local nobj_cave_point = minetest.get_perlin(np_cave)
+	local nobj_cave_point = mapgen.get_cave_point_perlin()
 	local air = 0 -- Consecutive air nodes found
 
 	local minp_schem, maxp_schem = nether.get_schematic_volume({x = target_x, y = 0, z = target_z}, nil, "nether_portal")
@@ -475,7 +486,7 @@ function nether.find_nether_ground_y(target_x, target_z, start_y, player_name)
 	local maxp = {x = maxp_schem.x, y = 0, z = maxp_schem.z}
 
 	for y = start_y, math_max(NETHER_FLOOR + BLEND, start_y - 4096), -1 do
-		local nval_cave = nobj_cave_point:get3d({x = target_x, y = y, z = target_z})
+		local nval_cave = nobj_cave_point:get_3d({x = target_x, y = y, z = target_z})
 
 		if nval_cave > TCAVE then -- Cavern
 			air = air + 1
@@ -499,8 +510,4 @@ function nether.find_nether_ground_y(target_x, target_z, start_y, player_name)
 	return math_max(start_y, NETHER_FLOOR + BLEND) -- Fallback
 end
 
--- We don't need to be gen-notified of temples because only dungeons will be generated
--- if a biome defines the dungeon nodes
-minetest.set_gen_notify({dungeon = true})
-
-minetest.register_on_generated(on_generated)
+minetest.register_on_generated(on_generated)

mapgen_decorations.lua

@@ -25,12 +25,28 @@
 -- emerged or not before the decoration was placed.
 local allow_lava_decorations = nether.useBiomes
 
-local _ = {name = "air",                     prob = 0}
-local A = {name = "air",                     prob = 255, force_place = true}
-local G = {name = "nether:glowstone",        prob = 255, force_place = true}
-local N = {name = "nether:rack",             prob = 255}
-local S = {name = "nether:sand",             prob = 255, force_place = true}
-local L = {name = "default:lava_source",     prob = 255, force_place = true}
+-- Keep compatibility with mapgen_nobiomes.lua, so hardcoding 128
+-- instead of using nether.mapgen.BLEND
+local decoration_ceiling = nether.DEPTH_CEILING - 128
+local decoration_floor   = nether.DEPTH_FLOOR   + 128
+
+local _  = {name = "air",                     prob = 0}
+local A  = {name = "air",                     prob = 255, force_place = true}
+local G  = {name = "nether:glowstone",        prob = 255, force_place = true}
+local N  = {name = "nether:rack",             prob = 255}
+local D  = {name = "nether:rack_deep",        prob = 255}
+local S  = {name = "nether:sand",             prob = 255, force_place = true}
+local L  = {name = "default:lava_source",     prob = 255, force_place = true}
+local F  = {name = "nether:fumarole",         prob = 255, force_place = true}
+local FS = {name = "nether:fumarole_slab",    prob = 255, force_place = true}
+local F1 = {name = "nether:fumarole_corner",  prob = 255, force_place = true, param2 = 0}
+local F2 = {name = "nether:fumarole_corner",  prob = 255, force_place = true, param2 = 1}
+local F3 = {name = "nether:fumarole_corner",  prob = 255, force_place = true, param2 = 2}
+local F4 = {name = "nether:fumarole_corner",  prob = 255, force_place = true, param2 = 3}
+local S1 = {name = "stairs:stair_netherrack", prob = 255, force_place = true, param2 = 5}
+local S2 = {name = "stairs:stair_netherrack", prob = 255, force_place = true, param2 = 7}
+local S3 = {name = "stairs:stair_netherrack", prob = 255, force_place = true, param2 = 12}
+local S4 = {name = "stairs:stair_netherrack", prob = 255, force_place = true, param2 = 16}
 
 
 -- =================
@@ -39,7 +55,7 @@ local L = {name = "default:lava_source",     prob = 255, force_place = true}
 
 local schematic_GlowstoneStalactite = {
     size = {x = 5, y = 10, z = 5},
-    data = {
+    data = { -- note that data is upside down
         _, _, _, _, _,
         _, _, _, _, _,
         _, _, _, _, _,
@@ -115,8 +131,8 @@ minetest.register_decoration({
     sidelen = 80,
     fill_ratio = 0.0003,
     biomes = {"nether_caverns"},
-    y_max = nether.DEPTH_CEILING, -- keep compatibility with mapgen_nobiomes.lua
-    y_min = nether.DEPTH_FLOOR,
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
     schematic = schematic_GlowstoneStalactite,
     flags = "place_center_x,place_center_z,force_placement,all_ceilings",
     place_offset_y=-3
@@ -129,10 +145,448 @@ minetest.register_decoration({
     sidelen = 80,
     fill_ratio = 0.0008,
     biomes = {"nether_caverns"},
-    y_max = nether.DEPTH_CEILING, -- keep compatibility with mapgen_nobiomes.lua
-    y_min = nether.DEPTH_FLOOR,
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
     schematic = schematic_GlowstoneStalactite,
     replacements = {["nether:glowstone"] = "nether:rack"},
     flags = "place_center_x,place_center_z,all_ceilings",
     place_offset_y=-3
 })
+
+
+local schematic_GreaterStalactite = {
+    size = {x = 3, y = 23, z = 3},
+    data = { -- note that data is upside down
+
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, D, _,
+        _, D, _,
+        _, D, _,
+        _, D, _,
+        D, D, D,
+        D, D, D,
+        D, D, D,
+        _, D, _,
+        _, _, _,
+        _, _, _,
+
+        _, D, _,  -- ypos 0, prob 85% (218/255)
+        _, D, _,  -- ypos 1, prob 85% (218/255)
+        _, D, _,  -- ypos 2, prob 85% (218/255)
+        _, D, _,  -- ypos 3, prob 85% (218/255)
+        _, D, _,  -- ypos 4, prob 85% (218/255)
+        _, D, _,  -- ypos 5, prob 85% (218/255)
+        _, D, _,  -- ypos 6, prob 85% (218/255)
+        _, D, _,  -- ypos 7, prob 85% (218/255)
+        _, D, _,  -- ypos 8, prob 85% (218/255)
+        _, D, D,  -- ypos 9, prob 50% (128/256) to make half of stalactites asymmetric
+        _, D, D,  -- ypos 10, prob 50% (128/256) to make half of stalactites asymmetric
+        _, D, D,  -- ypos 11, prob 50% (128/256) to make half of stalactites asymmetric
+        _, D, D,  -- ypos 12, prob 50% (128/256) to make half of stalactites asymmetric
+        D, D, D,  -- ypos 13, prob 75% (192/256)
+        D, D, D,  -- ypos 14, prob 75% (192/256)
+        D, D, D,  -- ypos 15, prob 100%
+        D, D, D,  -- ypos 16, prob 100%
+        D, D, D,  -- ypos 17, prob 100%
+        D, D, D,  -- ypos 18, prob 100%
+        D, D, D,  -- ypos 19, prob 75% (192/256)
+        D, D, D,  -- ypos 20, prob 85% (218/255)
+        _, D, D,  -- ypos 21, prob 50% (128/256) to make half of stalactites asymmetric
+        _, D, _,  -- ypos 22, prob 100%
+
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, _, _,
+        _, D, _,
+        _, D, _,
+        _, D, _,
+        _, D, _,
+        _, D, _,
+        D, D, D,
+        D, D, D,
+        D, D, D,
+        _, D, _,
+        _, D, _,
+        _, _, _,
+
+    },
+    -- Y-slice probabilities do not function correctly for ceiling schematic
+    -- decorations because they are inverted, so ypos numbers have been inverted
+    -- to match, and a larger offset in place_offset_y should be used (e.g. -3).
+    yslice_prob = {
+        {ypos = 21, prob = 128},
+        {ypos = 20, prob = 218},
+        {ypos = 19, prob = 192},
+        {ypos = 14, prob = 192},
+        {ypos = 13, prob = 192},
+        {ypos = 12, prob = 128},
+        {ypos = 11, prob = 128},
+        {ypos = 10, prob = 128},
+        {ypos =  9, prob = 128},
+        {ypos =  8, prob = 218},
+        {ypos =  7, prob = 218},
+        {ypos =  6, prob = 218},
+        {ypos =  5, prob = 218},
+        {ypos =  4, prob = 218},
+        {ypos =  3, prob = 218},
+        {ypos =  2, prob = 218},
+        {ypos =  1, prob = 218},
+        {ypos =  0, prob = 218}
+    }
+}
+
+
+
+-- A stalagmite is an upsidedown stalactite, so
+-- use the GreaterStalactite to create a ToweringStalagmite schematic
+local schematic_ToweringStalagmite = {
+    size = schematic_GreaterStalactite.size,
+    data = {},
+    yslice_prob = {}
+}
+local array_length = #schematic_GreaterStalactite.data + 1
+for i, node in ipairs(schematic_GreaterStalactite.data) do
+    schematic_ToweringStalagmite.data[array_length - i] = node
+end
+y_size = schematic_GreaterStalactite.size.y
+for i, node in ipairs(schematic_GreaterStalactite.yslice_prob) do
+    schematic_ToweringStalagmite.yslice_prob[i] = {
+        -- we can safely lower the prob. to gain more variance because floor based schematics
+        -- don't have the bug where missing lines moves them away from the surface
+        prob = schematic_GreaterStalactite.yslice_prob[i].prob - 20,
+        ypos = y_size - 1 - schematic_GreaterStalactite.yslice_prob[i].ypos
+    }
+end
+
+minetest.register_decoration({
+    name = "Deep-glowstone stalactite",
+    deco_type = "schematic",
+    place_on = "nether:rack_deep",
+    sidelen = 80,
+    fill_ratio = 0.0003,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = schematic_GlowstoneStalactite,
+    replacements = {["nether:rack"] = "nether:rack_deep", ["nether:glowstone"] = "nether:glowstone_deep"},
+    flags = "place_center_x,place_center_z,force_placement,all_ceilings",
+    place_offset_y=-3
+})
+
+minetest.register_decoration({
+    name = "Deep-glowstone stalactite outgrowth",
+    deco_type = "schematic",
+    place_on = "nether:glowstone_deep",
+    sidelen = 40,
+    fill_ratio = 0.15,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = {
+        size = {x = 1, y = 4, z = 1},
+        data = { G, G, G, G }
+    },
+    replacements = {["nether:glowstone"] = "nether:glowstone_deep"},
+    flags = "place_center_x,place_center_z,all_ceilings",
+})
+
+minetest.register_decoration({
+    name = "Deep-netherrack stalactite",
+    deco_type = "schematic",
+    place_on = "nether:rack_deep",
+    sidelen = 80,
+    fill_ratio = 0.0003,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = schematic_GlowstoneStalactite,
+    replacements = {["nether:rack"] = "nether:rack_deep", ["nether:glowstone"] = "nether:rack_deep"},
+    flags = "place_center_x,place_center_z,force_placement,all_ceilings",
+    place_offset_y=-3
+})
+
+minetest.register_decoration({
+    name = "Deep-netherrack towering stalagmite",
+    deco_type = "schematic",
+    place_on = "nether:rack_deep",
+    sidelen = 80,
+    fill_ratio = 0.001,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = schematic_ToweringStalagmite,
+    replacements = {["nether:basalt"] = "nether:rack_deep"},
+    flags = "place_center_x,place_center_z,force_placement,all_floors",
+    place_offset_y=-2
+})
+
+-- =======================================
+--    Concealed crevice / Lava sinkhole
+-- =======================================
+-- if player places a torch/block on this sand or digs it while standing on it, it sinks into lava
+
+if allow_lava_decorations then
+    minetest.register_decoration({
+        name = "Weak trap",
+        deco_type = "schematic",
+        place_on = "nether:rack",
+        sidelen = 80,
+        fill_ratio = 0.002,
+        biomes = {"nether_caverns"},
+        y_max = decoration_ceiling,
+        y_min = decoration_floor,
+        schematic = {
+            size = {x = 4, y = 7, z = 4},
+            data = { -- note that data is upside down
+                _, _, _, _,
+                _, _, _, _,
+                _, N, _, _,
+                _, N, N, _,
+                _, N, N, _,
+                _, N, N, _,
+                _, _, _, _,
+
+                _, N, _, _, -- make it look like a stalactite if it protrudes out the bottom of a landform
+                _, N, _, _,
+                N, L, N, _,
+                N, L, L, N,
+                N, L, L, N,
+                N, A, A, N,
+                _, S, S, _,
+
+                _, _, _, _,
+                _, _, _, _,
+                _, N, N, _,
+                N, L, L, N,
+                N, L, L, N,
+                N, A, A, N,
+                _, S, S, _,
+
+                _, _, _, _,
+                _, _, _, _,
+                _, _, _, _,
+                _, N, N, _,
+                _, N, N, _,
+                _, N, N, _,
+                _, _, _, _,
+            }
+        },
+        replacements = {["nether:glowstone"] = "nether:rack"},
+        flags = "place_center_x,place_center_z,force_placement, all_floors",
+        place_offset_y=-6,
+        rotation = "random"
+    })
+end
+
+
+-- ==========================
+--    Fumaroles (Chimneys)
+-- ==========================
+
+
+local replacements_slab = {}
+local replacements_full = {["nether:fumarole_slab"] = "nether:fumarole"}
+
+if allow_lava_decorations then
+    -- Minetest engine limitations mean any mesh or nodebox node (like nether:fumarole)
+    -- will light up if it has lava below it, so replace the air node over the lava with
+    -- a node that prevents light propagation.
+    -- (Unfortunately this also means if a player digs down to get the lava block it'll
+    -- look like the lighting wasn't set in the block above the lava)
+    replacements_slab["air"] = "nether:airlike_darkness"
+    replacements_full["air"] = "nether:airlike_darkness"
+else
+    -- Lava is frequently removed by the old mapgen, so put sand at the bottom
+    -- of fumaroles.
+    replacements_slab["default:lava_source"] = "nether:sand"
+    replacements_full["default:lava_source"] = "nether:sand"
+end
+
+
+local schematic_fumarole = {
+    size = {x = 3, y = 5, z = 3},
+    data = { -- note that data is upside down
+        _, _, _,
+        _, N, _,
+        _, N, _,
+        _, _, _,
+        _, _, _,
+
+        _, N, _,
+        N, L, N,
+        N, A, N,
+        _, F, _,
+        _,FS, _,
+
+        _, _, _,
+        _, N, _,
+        _, N, _,
+        _, _, _,
+        _, _, _,
+    },
+}
+
+-- Common fumarole decoration that's flush with the floor and spawns everywhere
+
+minetest.register_decoration({
+    name = "Sunken nether fumarole",
+    deco_type = "schematic",
+    place_on = {"nether:rack"},
+    sidelen = 80,
+    fill_ratio = 0.005,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = schematic_fumarole,
+    replacements = replacements_full,
+    flags = "place_center_x,place_center_z,all_floors",
+    place_offset_y=-4
+})
+
+
+-- Rarer formations of raised fumaroles in clumps
+
+local fumarole_clump_noise_offset = -0.58
+local fumarole_clump_noise = {
+    offset = fumarole_clump_noise_offset,
+    scale = 0.5,
+    spread = {x = 40, y = 40, z = 15},
+    octaves = 4,
+    persist = 0.65,
+    lacunarity = 2.0,
+}
+
+fumarole_clump_noise.offset = fumarole_clump_noise_offset - 0.035
+minetest.register_decoration({
+    name = "Raised Nether fumarole",
+    deco_type = "schematic",
+    place_on = {"nether:rack"},
+    sidelen = 8,
+    noise_params = fumarole_clump_noise,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = schematic_fumarole,
+    replacements = replacements_full,
+    flags = "place_center_x,place_center_z,all_floors",
+    place_offset_y=-3
+})
+
+fumarole_clump_noise.offset = fumarole_clump_noise_offset
+minetest.register_decoration({
+    name = "Half-raised Nether fumarole",
+    deco_type = "schematic",
+    place_on = {"nether:rack"},
+    sidelen = 8,
+    noise_params = fumarole_clump_noise,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = schematic_fumarole,
+    replacements = replacements_slab,
+    flags = "place_center_x,place_center_z,all_floors",
+    place_offset_y=-3
+})
+
+fumarole_clump_noise.offset = fumarole_clump_noise_offset - 0.035
+minetest.register_decoration({
+    name = "Nether fumarole mound",
+    deco_type = "schematic",
+    place_on = {"nether:rack"},
+    sidelen = 8,
+    noise_params = fumarole_clump_noise,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = {
+        size = {x = 4, y = 4, z = 4},
+        data = { -- note that data is upside down
+            _, _,  _,  _,
+            _, N,  N,  _,
+            _, _,  _,  _,
+            _, _,  _,  _,
+
+            _, S,  S,  _,
+            N, A,  A,  N,
+            _, S2, S1, _,
+            _, F2, F1, _,
+
+            _, S,  S,  _,
+            N, A,  A,  N,
+            _, S3, S4, _,
+            _, F3, F4, _,
+
+            _, _,  _,  _,
+            _, N,  N,  _,
+            _, _,  _,  _,
+            _, _,  _,  _
+        },
+        yslice_prob = {{ypos = 3, prob = 192}} -- occasionally leave the fumarole cap off
+    },
+    flags = "place_center_x,place_center_z,all_floors",
+    place_offset_y = -2
+})
+
+fumarole_clump_noise.offset = fumarole_clump_noise_offset - 0.01
+minetest.register_decoration({
+    name = "Double Nether fumarole",
+    deco_type = "schematic",
+    place_on = {"nether:rack"},
+    sidelen = 8,
+    noise_params = fumarole_clump_noise,
+    biomes = {"nether_caverns"},
+    y_max = decoration_ceiling,
+    y_min = decoration_floor,
+    schematic = {
+        size = {x = 4, y = 5, z = 4},
+        data = { -- note that data is upside down
+            _, _,  _,  _,
+            _, N,  N,  _,
+            _, _,  _,  _,
+            _, _,  _,  _,
+            _, _,  _,  _,
+
+            _, S,  S,  _,
+            N, A,  A,  N,
+            _, S2, S1, _,
+            _, F2, F,  _,
+            _, _,  FS, _,
+
+            _, S,  S,  _,
+            F, A,  A,  N, -- the F may add slight variance in landforms where it gets exposed
+            _, S3, S4, _,
+            _, F3, F4, _,
+            _, _,  _,  _,
+
+            _, _,  _,  _,
+            _, N,  N,  _,
+            _, _,  _,  _,
+            _, _,  _,  _,
+            _, _,  _,  _
+        }
+    },
+    flags = "place_center_x,place_center_z,all_floors",
+    place_offset_y = -2,
+    rotation = "random"
+})

mapgen_dungeons.lua

@@ -0,0 +1,333 @@
+--[[
+
+  Nether mod for minetest
+
+  All the Dungeon related functions used by the biomes-based mapgen are here.
+
+
+  Copyright (C) 2021 Treer
+
+  Permission to use, copy, modify, and/or distribute this software for
+  any purpose with or without fee is hereby granted, provided that the
+  above copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+  WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR
+  BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES
+  OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+  WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+  ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+  SOFTWARE.
+
+]]--
+
+
+-- We don't need to be gen-notified of temples because only dungeons will be generated
+-- if a biome defines the dungeon nodes
+minetest.set_gen_notify({dungeon = true})
+
+
+-- Content ids
+
+local c_air              = minetest.get_content_id("air")
+local c_netherrack       = minetest.get_content_id("nether:rack")
+local c_netherrack_deep  = minetest.get_content_id("nether:rack_deep")
+local c_dungeonbrick     = minetest.get_content_id("nether:brick")
+local c_dungeonbrick_alt = minetest.get_content_id("nether:brick_cracked")
+local c_netherbrick_slab = minetest.get_content_id("stairs:slab_nether_brick")
+local c_netherfence      = minetest.get_content_id("nether:fence_nether_brick")
+local c_glowstone        = minetest.get_content_id("nether:glowstone")
+local c_glowstone_deep   = minetest.get_content_id("nether:glowstone_deep")
+local c_lava_source      = minetest.get_content_id("default:lava_source")
+
+
+-- Misc math functions
+
+-- avoid needing table lookups each time a common math function is invoked
+local math_max, math_min  = math.max, math.min
+
+
+-- Dungeon excavation functions
+
+function is_dungeon_brick(node_id)
+	return node_id == c_dungeonbrick or node_id == c_dungeonbrick_alt
+end
+
+
+
+nether.mapgen.build_dungeon_room_list = function(data, area)
+
+	local result = {}
+
+	-- Unfortunately gennotify only returns dungeon rooms, not corridors.
+	-- We don't need to check for temples because only dungeons are generated in biomes
+	-- that define their own dungeon nodes.
+	local gennotify = minetest.get_mapgen_object("gennotify")
+	local roomLocations = gennotify["dungeon"] or {}
+
+	-- Excavation should still know to stop if a cave or corridor has removed the dungeon wall.
+	-- See MapgenBasic::generateDungeons in mapgen.cpp for max room sizes.
+	local maxRoomSize = 18
+	local maxRoomRadius = math.ceil(maxRoomSize / 2)
+
+	local xStride, yStride, zStride = 1, area.ystride, area.zstride
+	local minEdge, maxEdge = area.MinEdge, area.MaxEdge
+
+	for _, roomPos in ipairs(roomLocations) do
+
+		if area:containsp(roomPos) then -- this safety check does not appear to be necessary, but lets make it explicit
+
+			local room_vi = area:indexp(roomPos)
+			--data[room_vi] = minetest.get_content_id("default:torch") -- debug
+
+			local startPos = vector.new(roomPos)
+			if roomPos.y + 1 <= maxEdge.y and data[room_vi + yStride] == c_air then
+				-- The roomPos coords given by gennotify are at floor level, but whenever possible we
+				-- want to be performing searches a node higher than floor level to avoids dungeon chests.
+				startPos.y = startPos.y + 1
+				room_vi = area:indexp(startPos)
+			end
+
+			local bound_min_x = math_max(minEdge.x, roomPos.x - maxRoomRadius)
+			local bound_min_y = math_max(minEdge.y, roomPos.y - 1) -- room coords given by gennotify are on the floor
+			local bound_min_z = math_max(minEdge.z, roomPos.z - maxRoomRadius)
+
+			local bound_max_x = math_min(maxEdge.x, roomPos.x + maxRoomRadius)
+			local bound_max_y = math_min(maxEdge.y, roomPos.y + maxRoomSize) -- room coords given by gennotify are on the floor
+			local bound_max_z = math_min(maxEdge.z, roomPos.z + maxRoomRadius)
+
+			local room_min = vector.new(startPos)
+			local room_max = vector.new(startPos)
+
+			local vi = room_vi
+			while room_max.y < bound_max_y and data[vi + yStride] == c_air do
+				room_max.y = room_max.y + 1
+				vi = vi + yStride
+			end
+
+			vi = room_vi
+			while room_min.y > bound_min_y and data[vi - yStride] == c_air do
+				room_min.y = room_min.y - 1
+				vi = vi - yStride
+			end
+
+			vi = room_vi
+			while room_max.z < bound_max_z and data[vi + zStride] == c_air do
+				room_max.z = room_max.z + 1
+				vi = vi + zStride
+			end
+
+			vi = room_vi
+			while room_min.z > bound_min_z and data[vi - zStride] == c_air do
+				room_min.z = room_min.z - 1
+				vi = vi - zStride
+			end
+
+			vi = room_vi
+			while room_max.x < bound_max_x and data[vi + xStride] == c_air do
+				room_max.x = room_max.x + 1
+				vi = vi + xStride
+			end
+
+			vi = room_vi
+			while room_min.x > bound_min_x and data[vi - xStride] == c_air do
+				room_min.x = room_min.x - 1
+				vi = vi - xStride
+			end
+
+			local roomInfo = vector.new(roomPos)
+			roomInfo.minp = room_min
+			roomInfo.maxp = room_max
+			result[#result + 1] = roomInfo
+		end
+	end
+
+	return result;
+end
+
+-- Only partially excavates dungeons, the rest is left as an exercise for the player ;)
+-- (Corridors and the parts of rooms which extend beyond the emerge boundary will remain filled)
+nether.mapgen.excavate_dungeons = function(data, area, rooms)
+
+	local vi, node_id
+
+	-- any air from the native mapgen has been replaced by netherrack, but
+	-- we don't want this inside dungeons, so fill dungeon rooms with air
+	for _, roomInfo in ipairs(rooms) do
+
+		local room_min = roomInfo.minp
+		local room_max = roomInfo.maxp
+
+		for z = room_min.z, room_max.z do
+			for y = room_min.y, room_max.y do
+				vi = area:index(room_min.x, y, z)
+				for x = room_min.x, room_max.x do
+					node_id = data[vi]
+					if node_id == c_netherrack or node_id == c_netherrack_deep then data[vi] = c_air end
+					vi = vi + 1
+				end
+			end
+		end
+	end
+
+	-- clear netherrack from dungeon stairways
+	if #rooms > 0 then
+		local stairPositions = minetest.find_nodes_in_area(area.MinEdge, area.MaxEdge, minetest.registered_biomes["nether_caverns"].node_dungeon_stair)
+		for _, stairPos in ipairs(stairPositions) do
+			vi = area:indexp(stairPos)
+			for i = 1, 4 do
+				if stairPos.y + i > area.MaxEdge.y then break end
+				vi = vi + area.ystride
+				node_id = data[vi]
+				-- searching forward of the stairs could also be done
+				if node_id == c_netherrack or node_id == c_netherrack_deep then data[vi] = c_air end
+			end
+		end
+	end
+end
+
+-- Since we already know where all the rooms and their walls are, and have all the nodes stored
+-- in a voxelmanip already, we may as well add a little Nether flair to the dungeons found here.
+nether.mapgen.decorate_dungeons = function(data, area, rooms)
+
+	local xStride, yStride, zStride = 1, area.ystride, area.zstride
+	local minEdge, maxEdge = area.MinEdge, area.MaxEdge
+
+	for _, roomInfo in ipairs(rooms) do
+
+		local room_min, room_max = roomInfo.minp, roomInfo.maxp
+		local room_size = vector.distance(room_min, room_max)
+
+		if room_size > 10 then
+			local room_seed = roomInfo.x + 3 * roomInfo.z + 13 * roomInfo.y
+			local window_y  = roomInfo.y + math_min(2, room_max.y - roomInfo.y - 1)
+			local roomWidth  = room_max.x - room_min.x + 1
+			local roomLength = room_max.z - room_min.z + 1
+
+			if room_seed % 3 == 0 and room_max.y < maxEdge.y then
+				-- Glowstone chandelier (feel free to replace with a fancy schematic)
+				local vi = area:index(roomInfo.x, room_max.y + 1, roomInfo.z)
+				if is_dungeon_brick(data[vi]) then data[vi] = c_glowstone end
+
+			elseif room_seed % 4 == 0 and room_min.y > minEdge.y
+				   and room_min.x > minEdge.x and room_max.x < maxEdge.x
+				   and room_min.z > minEdge.z and room_max.z < maxEdge.z then
+				-- lava well (feel free to replace with a fancy schematic)
+				local vi = area:index(roomInfo.x, room_min.y, roomInfo.z)
+				if is_dungeon_brick(data[vi - yStride]) then
+					data[vi - yStride] = c_lava_source
+					if data[vi - zStride] == c_air then data[vi - zStride] = c_netherbrick_slab end
+					if data[vi + zStride] == c_air then data[vi + zStride] = c_netherbrick_slab end
+					if data[vi - xStride] == c_air then data[vi - xStride] = c_netherbrick_slab end
+					if data[vi + xStride] == c_air then data[vi + xStride] = c_netherbrick_slab end
+				end
+			end
+
+			-- Barred windows
+			if room_seed % 7 < 5 and roomWidth >= 5 and roomLength >= 5
+			   and window_y >= minEdge.y and window_y + 1 <= maxEdge.y
+			   and room_min.x > minEdge.x and room_max.x < maxEdge.x
+			   and room_min.z > minEdge.z and room_max.z < maxEdge.z then
+				--data[area:indexp(roomInfo)] = minetest.get_content_id("default:mese_post_light") -- debug
+
+				-- Can't use glass panes because they need the param data set.
+				-- Until whisper glass is added, every window will be made of netherbrick fence (rather
+				-- than material depending on room_seed)
+				local window_node = c_netherfence
+				--if c_netherglass ~= nil and room_seed % 20 >= 12 then window_node = c_crystallight end
+
+				local function placeWindow(vi, viOutsideOffset, windowNo)
+					if is_dungeon_brick(data[vi]) and is_dungeon_brick(data[vi + yStride]) then
+						data[vi] = window_node
+
+						if room_seed % 19 == windowNo then
+							-- place a glowstone light behind the window
+							local node_id = data[vi + viOutsideOffset]
+							if node_id == c_netherrack then
+								data[vi + viOutsideOffset] = c_glowstone
+							elseif node_id == c_netherrack_deep then
+								data[vi + viOutsideOffset] = c_glowstone_deep
+							end
+						end
+					end
+				end
+
+				local vi_min = area:index(room_min.x - 1, window_y, roomInfo.z)
+				local vi_max = area:index(room_max.x + 1, window_y, roomInfo.z)
+				local locations = {-zStride, zStride, -zStride + yStride, zStride + yStride}
+				for i, offset in ipairs(locations) do
+					placeWindow(vi_min + offset, -1, i)
+					placeWindow(vi_max + offset,  1, i + #locations)
+				end
+				vi_min = area:index(roomInfo.x, window_y, room_min.z - 1)
+				vi_max = area:index(roomInfo.x, window_y, room_max.z + 1)
+				locations = {-xStride, xStride, -xStride + yStride, xStride + yStride}
+				for i, offset in ipairs(locations) do
+					placeWindow(vi_min + offset, -zStride, i + #locations * 2)
+					placeWindow(vi_max + offset,  zStride, i + #locations * 3)
+				end
+			end
+
+			-- pillars or mezzanine floor
+			if room_seed % 43 > 10 and roomWidth >= 6 and roomLength >= 6 then
+
+				local pillar_vi    = {}
+				local pillarHeight = 0
+				local wallDist = 1 + math.floor((roomWidth + roomLength) / 14)
+
+				local roomHeight = room_max.y - room_min.y
+				if roomHeight >= 7 then
+					-- mezzanine floor
+					local mezzMax = {
+						x = room_min.x + math.floor(roomWidth / 7 * 4),
+						y = room_min.y + math.floor(roomHeight / 5 * 3),
+						z = room_max.z
+					}
+
+					pillarHeight = mezzMax.y - room_min.y - 1
+					pillar_vi = {
+						area:index(mezzMax.x, room_min.y, room_min.z + wallDist),
+						area:index(mezzMax.x, room_min.y, room_max.z - wallDist),
+					}
+
+					if is_dungeon_brick(data[pillar_vi[1] - yStride]) and is_dungeon_brick(data[pillar_vi[2] - yStride]) then
+						-- The floor of the dungeon looks like it exists (i.e. not erased by nether
+						-- cavern), so add the mezzanine floor
+						for z = 0, roomLength - 1 do
+							local vi = area:index(room_min.x, mezzMax.y, room_min.z + z)
+							for x = room_min.x, mezzMax.x do
+								if data[vi] == c_air then data[vi] = c_dungeonbrick end
+								vi = vi + 1
+							end
+						end
+					end
+
+				elseif roomHeight >= 4 then
+					-- 4 pillars
+					pillarHeight = roomHeight
+					pillar_vi = {
+						area:index(room_min.x + wallDist, room_min.y, room_min.z + wallDist),
+						area:index(room_min.x + wallDist, room_min.y, room_max.z - wallDist),
+						area:index(room_max.x - wallDist, room_min.y, room_min.z + wallDist),
+						area:index(room_max.x - wallDist, room_min.y, room_max.z - wallDist)
+					}
+				end
+
+				for i = #pillar_vi, 1, -1 do
+					if not is_dungeon_brick(data[pillar_vi[i] - yStride]) then
+						-- there's no dungeon floor under this pillar so skip it, it's probably been cut away by nether cavern.
+						table.remove(pillar_vi, i)
+					end
+				end
+				for y = 0, pillarHeight do
+					for _, vi in ipairs(pillar_vi) do
+						if data[vi + y * yStride] == c_air then data[vi + y * yStride] = c_dungeonbrick end
+					end
+				end
+			end
+
+			-- Weeds on the floor once Nether weeds are added
+		end
+	end
+end

mapgen_mantle.lua

@@ -0,0 +1,512 @@
+--[[
+
+  Nether mod for minetest
+
+  This file contains helper functions for generating the Mantle
+  (AKA center region), which are moved into a separate file to keep the
+  size of mapgen.lua manageable.
+
+
+  Copyright (C) 2021 Treer
+
+  Permission to use, copy, modify, and/or distribute this software for
+  any purpose with or without fee is hereby granted, provided that the
+  above copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+  WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR
+  BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES
+  OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+  WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+  ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+  SOFTWARE.
+
+]]--
+
+
+local debugf = nether.debug
+local mapgen = nether.mapgen
+local S      = nether.get_translator
+
+local BASALT_COLUMN_UPPER_LIMIT = mapgen.BASALT_COLUMN_UPPER_LIMIT
+local BASALT_COLUMN_LOWER_LIMIT = mapgen.BASALT_COLUMN_LOWER_LIMIT
+
+
+-- 2D noise for basalt formations
+local np_basalt = {
+	offset      =-0.85,
+	scale       = 1,
+	spread      = {x = 46, y = 46, z = 46},
+	seed        = 1000,
+	octaves     = 5,
+	persistence = 0.5,
+	lacunarity  = 2.6,
+	flags = "eased"
+}
+
+
+-- Buffers and objects we shouldn't recreate every on_generate
+
+local nobj_basalt = nil
+local nbuf_basalt = {}
+
+-- Content ids
+
+local c_air              = minetest.get_content_id("air")
+local c_netherrack_deep  = minetest.get_content_id("nether:rack_deep")
+local c_glowstone        = minetest.get_content_id("nether:glowstone")
+local c_lavasea_source   = minetest.get_content_id("nether:lava_source") -- same as lava but with staggered animation to look better as an ocean
+local c_lava_crust       = minetest.get_content_id("nether:lava_crust")
+local c_basalt           = minetest.get_content_id("nether:basalt")
+
+
+-- Math funcs
+local math_max, math_min, math_abs, math_floor = math.max, math.min, math.abs, math.floor -- avoid needing table lookups each time a common math function is invoked
+
+function random_unit_vector()
+	return vector.normalize({
+		x = math.random() - 0.5,
+		y = math.random() - 0.5,
+		z = math.random() - 0.5
+	})
+end
+
+-- returns the smallest component in the vector
+function vector_min(v)
+	return math_min(v.x, math_min(v.y, v.z))
+end
+
+
+-- Mantle mapgen functions (AKA Center region)
+
+-- Returns (absolute height, fractional distance from ceiling or sea floor)
+-- the fractional distance from ceiling or sea floor is a value between 0 and 1 (inclusive)
+-- Note it may find the most relevent sea-level - not necesssarily the one you are closest
+-- to, since the space above the sea reaches much higher than the depth below the sea.
+mapgen.find_nearest_lava_sealevel = function(y)
+	-- todo: put oceans near the bottom of chunks to improve ability to generate tunnels to the center
+	-- todo: constrain y to be not near the bounds of the nether
+	-- todo: add some random adj at each level, seeded only by the level height
+	local sealevel = math.floor((y + 100) / 200) * 200
+	--local sealevel = math.floor((y + 80) / 160) * 160
+	--local sealevel = math.floor((y + 120) / 240) * 240
+
+	local cavern_limits_fraction
+	local height_above_sea = y - sealevel
+	if height_above_sea >= 0 then
+		cavern_limits_fraction = math_min(1, height_above_sea / 95)
+	else
+		-- approaches 1 much faster as the lava sea is shallower than the cavern above it
+		cavern_limits_fraction = math_min(1, -height_above_sea / 40)
+	end
+
+	return sealevel, cavern_limits_fraction
+end
+
+
+
+
+mapgen.add_basalt_columns = function(data, area, minp, maxp)
+	-- Basalt columns are structures found in lava oceans, and the only way to obtain
+	-- nether basalt.
+	-- Their x, z position is determined by a 2d noise map and a 2d slice of the cave
+	-- noise (taken at lava-sealevel).
+
+	local x0, y0, z0 = minp.x, math_max(minp.y, nether.DEPTH_FLOOR),   minp.z
+	local x1, y1, z1 = maxp.x, math_min(maxp.y, nether.DEPTH_CEILING), maxp.z
+
+	local yStride = area.ystride
+	local yCaveStride = x1 - x0 + 1
+
+	local cavePerlin = mapgen.get_cave_point_perlin()
+	nobj_basalt = nobj_basalt or minetest.get_perlin_map(np_basalt, {x = yCaveStride, y = yCaveStride})
+	local nvals_basalt = nobj_basalt:get_2d_map_flat({x=minp.x, y=minp.z}, {x=yCaveStride, y=yCaveStride}, nbuf_basalt)
+
+	local nearest_sea_level, _ = mapgen.find_nearest_lava_sealevel(math_floor((y0 + y1) / 2))
+
+	local leeway = mapgen.CENTER_CAVERN_LIMIT * 0.18
+
+	for z = z0, z1 do
+		local noise2di = 1 + (z - z0) * yCaveStride
+
+		for x = x0, x1 do
+
+			local basaltNoise = nvals_basalt[noise2di]
+			if basaltNoise > 0 then
+				-- a basalt column is here
+
+				local abs_sealevel_cave_noise = math_abs(cavePerlin:get_3d({x = x, y = nearest_sea_level, z = z}))
+
+				-- Add Some quick deterministic noise to the column heights
+				-- This is probably not good noise, but it doesn't have to be.
+				local fastNoise = 17
+				fastNoise = 37 * fastNoise + y0
+				fastNoise = 37 * fastNoise + z
+				fastNoise = 37 * fastNoise + x
+				fastNoise = 37 * fastNoise + math_floor(basaltNoise * 32)
+
+				local columnHeight = basaltNoise * 18 + ((fastNoise % 3) - 1)
+
+				-- columns should drop below sealevel where lava rivers are flowing
+				-- i.e. anywhere abs_sealevel_cave_noise < BASALT_COLUMN_LOWER_LIMIT
+				-- And we'll also have it drop off near the edges of the lava ocean so that
+				-- basalt columns can only be found by the player reaching a lava ocean.
+				local lowerClip = (math_min(math_max(abs_sealevel_cave_noise, BASALT_COLUMN_LOWER_LIMIT - leeway), BASALT_COLUMN_LOWER_LIMIT + leeway) - BASALT_COLUMN_LOWER_LIMIT) / leeway
+				local upperClip = (math_min(math_max(abs_sealevel_cave_noise, BASALT_COLUMN_UPPER_LIMIT - leeway), BASALT_COLUMN_UPPER_LIMIT + leeway) - BASALT_COLUMN_UPPER_LIMIT) / leeway
+				local columnHeightAdj = lowerClip * -upperClip -- all are values between 1 and -1
+
+				columnHeight = columnHeight + math_floor(columnHeightAdj * 12 - 12)
+
+				local vi = area:index(x, y0, z) -- Initial voxelmanip index
+
+				for y = y0, y1 do -- Y loop first to minimise tcave & lava-sea calculations
+
+					if y < nearest_sea_level + columnHeight  then
+
+						local id = data[vi] -- Existing node
+						if id == c_lava_crust or id == c_lavasea_source or (id == c_air and y > nearest_sea_level) then
+							-- Avoid letting columns extend beyond the central region.
+							-- (checking node ids saves having to calculate abs_cave_noise_adjusted here
+							-- to test it against CENTER_CAVERN_LIMIT)
+							data[vi] = c_basalt
+						end
+					end
+
+					vi = vi + yStride
+				end
+			end
+
+			noise2di = noise2di + 1
+		end
+	end
+end
+
+
+-- returns an array of points from pos1 and pos2 which deviate from a straight line
+-- but which don't venture too close to a chunk boundary
+function generate_waypoints(pos1, pos2, minp, maxp)
+
+	local segSize = 10
+	local maxDeviation = 7
+	local minDistanceFromChunkWall = 5
+
+	local pathVec     = vector.subtract(pos2, pos1)
+	local pathVecNorm = vector.normalize(pathVec)
+	local pathLength  = vector.distance(pos1, pos2)
+	local minBound    = vector.add(minp, minDistanceFromChunkWall)
+	local maxBound    = vector.subtract(maxp, minDistanceFromChunkWall)
+
+	local result = {}
+	result[1] = pos1
+
+	local segmentCount = math_floor(pathLength / segSize)
+	for i = 1, segmentCount do
+		local waypoint = vector.add(pos1, vector.multiply(pathVec, i / (segmentCount + 1)))
+
+		-- shift waypoint a few blocks in a random direction orthogonally to the pathVec, to make the path crooked.
+		local crossProduct
+		repeat
+			crossProduct = vector.normalize(vector.cross(pathVecNorm, random_unit_vector()))
+		until vector.length(crossProduct) > 0
+		local deviation = vector.multiply(crossProduct, math.random(1, maxDeviation))
+		waypoint = vector.add(waypoint, deviation)
+		waypoint = {
+			x = math_min(maxBound.x, math_max(minBound.x, waypoint.x)),
+			y = math_min(maxBound.y, math_max(minBound.y, waypoint.y)),
+			z = math_min(maxBound.z, math_max(minBound.z, waypoint.z))
+		}
+
+		result[#result + 1] = waypoint
+	end
+
+	result[#result + 1] = pos2
+	return result
+end
+
+
+function excavate_pathway(data, area, nether_pos, center_pos, minp, maxp)
+
+	local ystride = area.ystride
+	local zstride = area.zstride
+
+	math.randomseed(nether_pos.x + 10 * nether_pos.y + 100 * nether_pos.z) -- so each tunnel generates deterministically (this doesn't have to be a quality seed)
+	local dist = math_floor(vector.distance(nether_pos, center_pos))
+	local waypoints = generate_waypoints(nether_pos, center_pos, minp, maxp)
+
+	-- First pass: record path details
+	local linedata = {}
+	local last_pos = {}
+	local line_index = 1
+	local first_filled_index, boundary_index, last_filled_index
+	for i = 0, dist do
+		-- Bresenham's line would be good here, but too much lua code
+		local waypointProgress = (#waypoints - 1) * i / dist
+		local segmentIndex = math_min(math_floor(waypointProgress) + 1, #waypoints - 1) -- from the integer portion of waypointProgress
+		local segmentInterp = waypointProgress - (segmentIndex - 1)                     -- the remaining fractional portion
+		local segmentStart = waypoints[segmentIndex]
+		local segmentVector = vector.subtract(waypoints[segmentIndex + 1], segmentStart)
+		local pos = vector.round(vector.add(segmentStart, vector.multiply(segmentVector, segmentInterp)))
+
+		if not vector.equals(pos, last_pos) then
+			local vi = area:indexp(pos)
+			local node_id = data[vi]
+			linedata[line_index] = {
+				pos = pos,
+				vi = vi,
+				node_id = node_id
+			}
+			if boundary_index == nil and node_id == c_netherrack_deep then
+				boundary_index = line_index
+			end
+			if node_id == c_air then
+				if boundary_index ~= nil and last_filled_index == nil then
+					last_filled_index = line_index
+				end
+			else
+				if first_filled_index == nil then
+					first_filled_index = line_index
+				end
+			end
+			line_index = line_index + 1
+			last_pos = pos
+		end
+	end
+	first_filled_index = first_filled_index or 1
+	last_filled_index  = last_filled_index  or #linedata
+	boundary_index     = boundary_index     or last_filled_index
+
+
+	-- limit tunnel radius to roughly the closest that startPos or stopPos comes to minp-maxp, so we
+	-- don't end up exceeding minp-maxp and having excavation filled in when the next chunk is generated.
+	local startPos, stopPos = linedata[first_filled_index].pos, linedata[last_filled_index].pos
+	local radiusLimit = vector_min(vector.subtract(startPos, minp))
+	radiusLimit = math_min(radiusLimit, vector_min(vector.subtract(stopPos, minp)))
+	radiusLimit = math_min(radiusLimit, vector_min(vector.subtract(maxp, startPos)))
+	radiusLimit = math_min(radiusLimit, vector_min(vector.subtract(maxp, stopPos)))
+
+	if radiusLimit < 4 then -- This is a logic check, ignore it. It could be commented out
+		-- 4 is (79 - 75), and values less than 4 shouldn't be possible if sampling-skip was 10
+		-- i.e. if sampling-skip was 10 then {5, 15, 25, 35, 45, 55, 65, 75} should be sampled from possible positions 0 to 79
+		debugf("Error: radiusLimit %s is smaller then half the sampling distance. min %s, max %s, start %s, stop %s", radiusLimit, minp, maxp, startPos, stopPos)
+	end
+	radiusLimit = radiusLimit + 1 -- chunk walls wont be visibly flat if the radius only exceeds it a little ;)
+
+	-- Second pass: excavate
+	local start_index, stop_index = math_max(1, first_filled_index - 2), math_min(#linedata, last_filled_index + 3)
+	for i = start_index, stop_index, 3 do
+
+		-- Adjust radius so that tunnels start wide but thin out in the middle
+		local distFromEnds = 1 - math_abs(((start_index + stop_index) / 2) - i) / ((stop_index - start_index) / 2) -- from 0 to 1, with 0 at ends and 1 in the middle
+		-- Have it more flaired at the ends, rather than linear.
+		-- i.e. sizeAdj approaches 1 quickly as distFromEnds increases
+		local distFromMiddle = 1 - distFromEnds
+		local sizeAdj = 1 - (distFromMiddle * distFromMiddle * distFromMiddle)
+
+		local radius = math_min(radiusLimit, math.random(50 - (25 * sizeAdj), 80 - (45 * sizeAdj)) / 10)
+		local radiusSquared = radius * radius
+		local radiusCeil = math_floor(radius + 0.5)
+
+		linedata[i].radius = radius             -- Needed in third pass
+		linedata[i].distFromEnds = distFromEnds -- Needed in third pass
+
+		local vi = linedata[i].vi
+		for z = -radiusCeil, radiusCeil do
+			local vi_z = vi + z * zstride
+			for y = -radiusCeil, radiusCeil do
+				local vi_zy = vi_z + y * ystride
+				local xSquaredLimit = radiusSquared - (z * z + y * y)
+				for x = -radiusCeil, radiusCeil do
+					if x * x < xSquaredLimit then
+						data[vi_zy + x] = c_air
+					end
+				end
+			end
+		end
+
+	end
+
+	-- Third pass: decorate
+	-- Add glowstones to make tunnels to the mantle easier to find
+	-- https://i.imgur.com/sRA28x7.jpg
+	for i = start_index, stop_index, 3 do
+		if linedata[i].distFromEnds < 0.3 then
+			local glowcount = 0
+			local radius = linedata[i].radius
+			for _ = 1, 20 do
+				local testPos = vector.round(vector.add(linedata[i].pos, vector.multiply(random_unit_vector(), radius + 0.5)))
+				local vi = area:indexp(testPos)
+				if data[vi] ~= c_air then
+					data[vi] = c_glowstone
+					glowcount = glowcount + 1
+				--else
+				--	data[vi] = c_debug
+				end
+				if glowcount >= 2 then break end
+			end
+		end
+	end
+
+end
+
+
+-- excavates a tunnel connecting the Primary or Secondary region with the mantle / central region
+-- if a suitable path is found.
+-- Returns true if successful
+mapgen.excavate_tunnel_to_center_of_the_nether = function(data, area, nvals_cave, minp, maxp)
+
+	local result = false
+	local extent = vector.subtract(maxp, minp)
+	local skip = 10 -- sampling rate of 1 in 10
+
+	local highest = -1000
+	local lowest  =  1000
+	local lowest_vi
+	local highest_vi
+
+	local yCaveStride = maxp.x - minp.x + 1
+	local zCaveStride = yCaveStride * yCaveStride
+
+	local vi_offset = area:indexp(vector.add(minp, math_floor(skip / 2))) -- start half the sampling distance away from minp
+	local vi, ni
+
+	for y = 0, extent.y - 1, skip do
+		local sealevel = mapgen.find_nearest_lava_sealevel(minp.y + y)
+
+		if minp.y + y > sealevel then -- only create tunnels above sea level
+			for z = 0, extent.z - 1, skip do
+
+				vi = vi_offset + y * area.ystride + z * area.zstride
+				ni = z * zCaveStride + y * yCaveStride + 1
+				for x = 0, extent.x - 1, skip do
+
+					local noise = math_abs(nvals_cave[ni])
+					if noise < lowest then
+						lowest = noise
+						lowest_vi = vi
+					end
+					if noise > highest then
+						highest = noise
+						highest_vi = vi
+					end
+					ni = ni + skip
+					vi = vi + skip
+				end
+			end
+		end
+	end
+
+	if lowest < mapgen.CENTER_CAVERN_LIMIT and highest > mapgen.TCAVE + 0.03 then
+
+		local mantle_y = area:position(lowest_vi).y
+		local _, cavern_limit_distance = mapgen.find_nearest_lava_sealevel(mantle_y)
+		local _, centerRegionLimit_adj = mapgen.get_mapgenblend_adjustments(mantle_y)
+
+		 -- cavern_noise_adj gets added to noise value instead of added to the limit np_noise
+		 -- is compared against, so subtract centerRegionLimit_adj instead of adding
+		local cavern_noise_adj =
+			mapgen.CENTER_REGION_LIMIT * (cavern_limit_distance * cavern_limit_distance * cavern_limit_distance) -
+			centerRegionLimit_adj
+
+		if lowest + cavern_noise_adj < mapgen.CENTER_CAVERN_LIMIT then
+			excavate_pathway(data, area, area:position(highest_vi), area:position(lowest_vi), minp, maxp)
+			result = true
+		end
+	end
+	return result
+end
+
+
+-- an enumerated list of the different regions in the nether
+mapgen.RegionEnum = {
+	OVERWORLD     = {name = "overworld",      desc = S("The Overworld") },   -- Outside the Nether / none of the regions in the Nether
+	POSITIVE      = {name = "positive",       desc = S("Positive nether") }, -- The classic nether caverns are here - where cavePerlin > 0.6
+	POSITIVESHELL = {name = "positive shell", desc = S("Shell between positive nether and center region") }, -- the nether side of the wall/buffer area separating classic nether from the mantle
+	CENTER        = {name = "center",         desc = S("Center/Mantle, inside cavern") },
+	CENTERSHELL   = {name = "center shell",   desc = S("Center/Mantle, but outside the caverns") }, -- the mantle side of the wall/buffer area separating the positive and negative regions from the center region
+	NEGATIVE      = {name = "negative",       desc = S("Negative nether") }, -- Secondary/spare region - where cavePerlin < -0.6
+	NEGATIVESHELL = {name = "negative shell", desc = S("Shell between negative nether and center region") } -- the spare region side of the wall/buffer area separating the negative region from the mantle
+}
+
+
+-- Returns (region, noise) where region is a value from mapgen.RegionEnum
+-- and noise is the unadjusted cave perlin value
+mapgen.get_region = function(pos)
+
+	if pos.y > nether.DEPTH_CEILING or pos.y < nether.DEPTH_FLOOR then
+		return mapgen.RegionEnum.OVERWORLD, nil
+	end
+
+	local caveNoise = mapgen.get_cave_perlin_at(pos)
+	local sealevel, cavern_limit_distance = mapgen.find_nearest_lava_sealevel(pos.y)
+	local tcave_adj, centerRegionLimit_adj = mapgen.get_mapgenblend_adjustments(pos.y)
+	local tcave   = mapgen.TCAVE + tcave_adj
+	local tmantle = mapgen.CENTER_REGION_LIMIT + centerRegionLimit_adj
+
+	-- cavern_noise_adj gets added to noise value instead of added to the limit np_noise
+	-- is compared against, so subtract centerRegionLimit_adj instead of adding
+	local cavern_noise_adj =
+		mapgen.CENTER_REGION_LIMIT * (cavern_limit_distance * cavern_limit_distance * cavern_limit_distance) -
+		centerRegionLimit_adj
+
+	local region
+	if caveNoise > tcave then
+		region = mapgen.RegionEnum.POSITIVE
+	elseif -caveNoise > tcave then
+		region = mapgen.RegionEnum.NEGATIVE
+	elseif math_abs(caveNoise) < tmantle then
+
+		if math_abs(caveNoise) + cavern_noise_adj < mapgen.CENTER_CAVERN_LIMIT then
+			region = mapgen.RegionEnum.CENTER
+		else
+			region = mapgen.RegionEnum.CENTERSHELL
+		end
+
+	elseif caveNoise > 0 then
+		region = mapgen.RegionEnum.POSITIVESHELL
+	else
+		region = mapgen.RegionEnum.NEGATIVESHELL
+	end
+
+	return region, caveNoise
+end
+
+
+minetest.register_chatcommand("nether_whereami",
+	{
+		description = S("Describes which region of the nether the player is in"),
+		privs = {debug = true},
+		func = function(name, param)
+
+			local player = minetest.get_player_by_name(name)
+			if player == nil then return false, S("Unknown player position") end
+			local playerPos = vector.round(player:get_pos())
+
+			local region, caveNoise                = mapgen.get_region(playerPos)
+			local seaLevel, cavernLimitDistance    = mapgen.find_nearest_lava_sealevel(playerPos.y)
+			local tcave_adj, centerRegionLimit_adj = mapgen.get_mapgenblend_adjustments(playerPos.y)
+
+			local seaDesc = ""
+			local boundaryDesc = ""
+			local perlinDesc = ""
+
+			if region ~= mapgen.RegionEnum.OVERWORLD then
+
+				local seaPos = playerPos.y - seaLevel
+				if seaPos > 0 then
+					seaDesc = S(", @1m above lava-sea level", seaPos)
+				else
+					seaDesc = S(", @1m below lava-sea level", seaPos)
+				end
+
+				if tcave_adj > 0 then
+					boundaryDesc = S(", approaching y boundary of Nether")
+				end
+
+				perlinDesc = S("[Perlin @1] ", (math_floor(caveNoise * 1000) / 1000))
+			end
+
+			return true, S("@1@2@3@4", perlinDesc, region.desc, seaDesc, boundaryDesc)
+		end
+	}
+)

mapgen_nobiomes.lua

@@ -2,6 +2,12 @@
 
   Nether mod for minetest
 
+  "mapgen_nobiomes.lua" is the legacy version of the mapgen, only used
+    in older versions of Minetest or in v6 worlds.
+  "mapgen.lua" is the modern biomes-based Nether mapgen, which
+    requires Minetest v5.1 or greater
+
+
   Copyright (C) 2013 PilzAdam
 
   Permission to use, copy, modify, and/or distribute this software for
@@ -190,8 +196,7 @@ minetest.register_on_generated(function(minp, maxp, seed)
 
 	vm:set_data(data)
 
-	-- avoid generating decorations on the underside of the bottom of the nether
-	if minp.y > NETHER_FLOOR and maxp.y < NETHER_CEILING then minetest.generate_decorations(vm) end
+	minetest.generate_decorations(vm)
 
 	vm:set_lighting({day = 0, night = 0}, minp, maxp)
 	vm:calc_lighting()
@@ -211,7 +216,7 @@ function nether.find_nether_ground_y(target_x, target_z, start_y, player_name)
 	local maxp = {x = maxp_schem.x, y = 0, z = maxp_schem.z}
 
 	for y = start_y, math.max(NETHER_FLOOR + BLEND, start_y - 4096), -1 do
-		local nval_cave = nobj_cave_point:get3d({x = target_x, y = y, z = target_z})
+		local nval_cave = nobj_cave_point:get_3d({x = target_x, y = y, z = target_z})
 
 		if nval_cave > TCAVE then -- Cavern
 			air = air + 1

mod.conf

@@ -1 +1,4 @@
 name = nether
+description = Adds a deep underground realm with different mapgen that you can reach with obsidian portals.
+depends = stairs, default
+optional_depends = moreblocks, mesecons, loot, dungeon_loot, doc_basics, fire, climate_api, ethereal

nether_api.txt

@@ -0,0 +1,78 @@
+Modding/interop guide to Nether
+===============================
+
+For portals API see portal_api.txt
+
+The Nether mod exposes some of its functions and data via the lua global
+`nether` and `nether.mapgen`
+
+
+* `nether.DEPTH_CEILING`: [read-only] Y value of the top of the Nether.
+
+* `nether.DEPTH_FLOOR`: [read-only] Y value of the bottom of the Nether.
+
+* `nether.DEPTH_FLOOR_LAYERS`: [writable] Gives the bottom Y of all
+  locations that wish to be considered part of the Nether.
+  DEPTH_FLOOR_LAYERS Allows mods to insert extra layers below the
+  Nether, by knowing where their layer ceiling should start, and letting
+  the layers be included in effects which only happen in the Nether.
+  If a mod wishes to add a layer below the Nether it should read
+  `nether.DEPTH_FLOOR_LAYERS` to find the bottom Y of the Nether and any
+  other layers already under the Nether. The mod should leave a small gap
+  between DEPTH_FLOOR_LAYERS and its ceiling (e.g. use DEPTH_FLOOR_LAYERS - 6
+  for its ceiling Y, so there is room to shift edge-case biomes), then set
+  `nether.DEPTH_FLOOR_LAYERS` to reflect the mod's floor Y value, and call
+  `shift_existing_biomes()` with DEPTH_FLOOR_LAYERS as the `floor_y` argument.
+
+* `nether.NETHER_REALM_ENABLED`: [read-only] Gets the value of the "Enable
+  Nether realm & portal" setting the nether mod exposes in Minetest's
+  "All Settings" -> "Mods" -> "nether" options.
+  When false, the entire nether mapgen is disabled (not run), and the portal
+  to it is not registered. Reasons someone might disable the Nether realm
+  include if a nether-layer mod was to be used as the Nether instead, or if
+  the portal mechanic was desired in a game without the Nether, etc.
+
+* `nether.useBiomes`: [read-only] When this is false, the Nether interop
+  functions below are not available (nil).
+  Indicates that the biomes-enabled mapgen is in use. The Nether mod falls back
+  to older mapgen code for v6 maps and old versions of Minetest, the older
+  mapgen code doesn't use biomes and doesn't provide API/interop functions.
+
+
+Mapgen functions available when nether.useBiomes is true
+--------------------------------------------------------
+
+The following functions are nil if `nether.useBiomes` is false,
+and also nil if `nether.NETHER_REALM_ENABLED` is false.
+
+* `nether.mapgen.shift_existing_biomes(floor_y, ceiling_y)` Move any existing
+  biomes out of the y-range specified by `floor_y` and `ceiling_y`.
+
+* `nether.mapgen.get_region(pos)`: Returns two values, (region, noise) where
+  `region` is a value from `nether.mapgen.RegionEnum` and `noise` is the
+  unadjusted cave perlin value.
+    * `nether.mapgen.RegionEnum` values are tables which contain an invariant
+      `name` and a localized `desc`. Current region names include overworld,
+      positive, positive shell, center, center shell, negative, and negative
+      shell.
+      "positive" corresponds to conventional Nether caverns, and "center"
+      corresponds to the Mantle region.
+
+* `nether.mapgen.get_cave_point_perlin()`: Returns the PerlinNoise object for
+  the Nether's cavern noise.
+
+* `nether.mapgen.get_cave_perlin_at(pos)`: Returns the Nether cavern noise
+  value at a given 3D position.
+
+
+Other mapgen functions
+-------------------------------------------
+
+If the Nether realm is enabled, then this function will be available
+regardless of whether `nether.useBiomes` is true:
+
+* `nether.find_nether_ground_y(target_x, target_z, start_y, player_name)`
+  Uses knowledge of the nether mapgen algorithm to return a suitable ground
+  level for placing a portal.
+    * `player_name` is optional, allowing a player to spawn a remote portal
+      in their own protected areas.

nodes.lua

@@ -75,6 +75,16 @@ minetest.register_node("nether:rack", {
 	sounds = default.node_sound_stone_defaults(),
 })
 
+-- Deep Netherrack, found in the mantle / central magma layers
+minetest.register_node("nether:rack_deep", {
+	description = S("Deep Netherrack"),
+	_doc_items_longdesc = S("Netherrack from deep in the mantle"),
+	tiles = {"nether_rack_deep.png"},
+	is_ground_content = true,
+	groups = {cracky = 3, level = 2},
+	sounds = default.node_sound_stone_defaults(),
+})
+
 minetest.register_node("nether:sand", {
 	description = S("Nethersand"),
 	tiles = {"nether_sand.png"},
@@ -95,6 +105,17 @@ minetest.register_node("nether:glowstone", {
 	sounds = default.node_sound_glass_defaults(),
 })
 
+-- Deep glowstone, found in the mantle / central magma layers
+minetest.register_node("nether:glowstone_deep", {
+	description = S("Deep Glowstone"),
+	tiles = {"nether_glowstone_deep.png"},
+	is_ground_content = true,
+	light_source = 14,
+	paramtype = "light",
+	groups = {cracky = 3, oddly_breakable_by_hand = 3},
+	sounds = default.node_sound_glass_defaults(),
+})
+
 minetest.register_node("nether:brick", {
 	description = S("Nether Brick"),
 	tiles = {"nether_brick.png"},
@@ -103,6 +124,23 @@ minetest.register_node("nether:brick", {
 	sounds = default.node_sound_stone_defaults(),
 })
 
+minetest.register_node("nether:brick_compressed", {
+	description = S("Compressed Netherbrick"),
+	tiles = {"nether_brick_compressed.png"},
+	groups = {cracky = 3, level = 2},
+	is_ground_content = false,
+	sounds = default.node_sound_stone_defaults(),
+})
+
+-- A decorative node which can only be obtained from dungeons or structures
+minetest.register_node("nether:brick_cracked", {
+	description = S("Cracked Nether Brick"),
+	tiles = {"nether_brick_cracked.png"},
+	is_ground_content = false,
+	groups = {cracky = 2, level = 2},
+	sounds = default.node_sound_stone_defaults(),
+})
+
 local fence_texture =
 	"default_fence_overlay.png^nether_brick.png^default_fence_overlay.png^[makealpha:255,126,126"
 
@@ -123,6 +161,13 @@ minetest.register_node("nether:fence_nether_brick", {
 	sounds = default.node_sound_stone_defaults(),
 })
 
+minetest.register_node("nether:brick_deep", {
+	description = S("Deep Nether Brick"),
+	tiles = {"nether_brick_deep.png"},
+	is_ground_content = false,
+	groups = {cracky = 2, level = 2},
+	sounds = default.node_sound_stone_defaults()
+})
 
 -- Register stair and slab
 
@@ -133,6 +178,18 @@ stairs.register_stair_and_slab(
 	{"nether_brick.png"},
 	S("Nether Stair"),
 	S("Nether Slab"),
+	default.node_sound_stone_defaults(),
+	nil,
+	S("Inner Nether Stair"),
+	S("Outer Nether Stair")
+)
+
+stairs.register_stair(
+	"netherrack",
+	"nether:rack",
+	{cracky = 2, level = 2},
+	{"nether_rack.png"},
+	S("Netherrack stair"),
 	default.node_sound_stone_defaults()
 )
 
@@ -149,22 +206,577 @@ if minetest.get_modpath("moreblocks") then
 end
 
 
--- Crafting
+-- Mantle nodes
 
-minetest.register_craft({
-	output = "nether:brick 4",
-	recipe = {
-		{"nether:rack", "nether:rack"},
-		{"nether:rack", "nether:rack"},
-	}
-})
-
-minetest.register_craft({
-	output = "nether:fence_nether_brick 6",
-	recipe = {
-		{"nether:brick", "nether:brick", "nether:brick"},
-		{"nether:brick", "nether:brick", "nether:brick"},
+-- Nether basalt is intended as a valuable material and possible portalstone - an alternative to
+-- obsidian that's available for other mods to use.
+-- It cannot be found in the regions of the nether where Nether portals link to, so requires a journey to obtain.
+minetest.register_node("nether:basalt", {
+	description = S("Nether Basalt"),
+	_doc_items_longdesc = S("Columns of dark basalt found only in magma oceans deep within the Nether."),
+	tiles = {
+		"nether_basalt.png",
+		"nether_basalt.png",
+		"nether_basalt_side.png",
+		"nether_basalt_side.png",
+		"nether_basalt_side.png",
+		"nether_basalt_side.png"
 	},
+	is_ground_content = true,
+	groups = {cracky = 1, level = 3}, -- set proper digging times and uses, and maybe explosion immune if api handles that
+	on_blast = function() --[[blast proof]] end,
+	sounds = default.node_sound_stone_defaults(),
+})
+
+-- Potentially a portalstone, but will also be a stepping stone between basalt
+-- and chiseled basalt.
+-- It can only be introduced by the biomes-based mapgen, since it requires the
+-- MT 5.0 world-align texture features.
+minetest.register_node("nether:basalt_hewn", {
+	description = S("Hewn Basalt"),
+	_doc_items_longdesc = S("A rough cut solid block of Nether Basalt."),
+	tiles = {{
+		name        = "nether_basalt_hewn.png",
+		align_style = "world",
+		scale       = 2
+	}},
+	inventory_image = minetest.inventorycube(
+		"nether_basalt_hewn.png^[sheet:2x2:0,0",
+		"nether_basalt_hewn.png^[sheet:2x2:0,1",
+		"nether_basalt_hewn.png^[sheet:2x2:1,1"
+	),
+	is_ground_content = false,
+	groups = {cracky = 1, level = 2},
+	on_blast = function() --[[blast proof]] end,
+	sounds = default.node_sound_stone_defaults(),
+})
+
+-- Chiselled basalt is intended as a portalstone - an alternative to obsidian that's
+-- available for other mods to use. It is crafted from Hewn Basalt.
+-- It should only be introduced by the biomes-based mapgen, since in future it may
+-- require the MT 5.0 world-align texture features.
+minetest.register_node("nether:basalt_chiselled", {
+	description = S("Chiselled Basalt"),
+	_doc_items_longdesc = S("A finely finished block of solid Nether Basalt."),
+	tiles = {
+		"nether_basalt_chiselled_top.png",
+		"nether_basalt_chiselled_top.png" .. "^[transformFY",
+		"nether_basalt_chiselled_side.png",
+		"nether_basalt_chiselled_side.png",
+		"nether_basalt_chiselled_side.png",
+		"nether_basalt_chiselled_side.png"
+	},
+	inventory_image = minetest.inventorycube(
+		"nether_basalt_chiselled_top.png",
+		"nether_basalt_chiselled_side.png",
+		"nether_basalt_chiselled_side.png"
+	),
+	paramtype2 = "facedir",
+	is_ground_content = false,
+	groups = {cracky = 1, level = 2},
+	on_blast = function() --[[blast proof]] end,
+	sounds = default.node_sound_stone_defaults(),
 })
 
 
+-- Lava-sea source
+-- This is a lava source using a different animated texture so that each node
+-- is out of phase in its animation from its neighbor. This prevents the magma
+-- ocean from visually clumping together into a patchwork of 16x16 squares.
+-- It can only be used by the biomes-based mapgen, since it requires the MT 5.0
+-- world-align texture features.
+local lavasea_source = {}
+local lava_source = minetest.registered_nodes["default:lava_source"]
+for key, value in pairs(lava_source) do lavasea_source[key] = value end
+lavasea_source.name = nil
+lavasea_source.tiles = {
+	{
+		name             = "nether_lava_source_animated.png",
+		backface_culling = false,
+		align_style      = "world",
+		scale            = 2,
+		animation = {
+			type     = "vertical_frames",
+			aspect_w = 32,
+			aspect_h = 32,
+			length   = 3.0,
+		},
+	},
+	{
+		name             = "nether_lava_source_animated.png",
+		backface_culling = true,
+		align_style      = "world",
+		scale            = 2,
+		animation = {
+			type     = "vertical_frames",
+			aspect_w = 32,
+			aspect_h = 32,
+			length   = 3.0,
+		},
+	},
+}
+lavasea_source.groups = { not_in_creative_inventory = 1 } -- Avoid having two lava source blocks in the inv.
+for key, value in pairs(lava_source.groups) do lavasea_source.groups[key] = value end
+lavasea_source.liquid_alternative_source = "nether:lava_source"
+lavasea_source.inventory_image = minetest.inventorycube(
+	"nether_lava_source_animated.png^[sheet:2x16:0,0",
+	"nether_lava_source_animated.png^[sheet:2x16:0,1",
+	"nether_lava_source_animated.png^[sheet:2x16:1,1"
+)
+minetest.register_node("nether:lava_source", lavasea_source)
+
+
+-- a place to store the original ABM function so nether.cool_lava() can call it
+local original_cool_lava_action
+
+nether.cool_lava = function(pos, node)
+
+	local pos_above = {x = pos.x, y = pos.y + 1, z = pos.z}
+	local node_above = minetest.get_node(pos_above)
+
+	-- Evaporate water sitting above lava, if it's in the Nether.
+	-- (we don't want Nether mod to affect overworld lava mechanics)
+	if minetest.get_item_group(node_above.name, "water") > 0 and
+		pos.y < nether.DEPTH_CEILING and pos.y > nether.DEPTH_FLOOR_LAYERS then
+		-- cools_lava might be a better group to check for, but perhaps there's
+		-- something in that group that isn't a liquid and shouldn't be evaporated?
+		minetest.swap_node(pos_above, {name="air"})
+	end
+
+	-- add steam to cooling lava
+	minetest.add_particlespawner({
+		amount = 20,
+		time = 0.15,
+		minpos = {x=pos.x - 0.4, y=pos.y - 0,   z=pos.z - 0.4},
+		maxpos = {x=pos.x + 0.4, y=pos.y + 0.5, z=pos.z + 0.4},
+		minvel = {x = -0.5, y = 0.5, z = -0.5},
+		maxvel = {x =  0.5, y = 1.5, z =  0.5},
+		minacc = {x = 0, y = 0.1, z = 0},
+		maxacc = {x = 0, y = 0.2, z = 0},
+		minexptime = 0.5,
+		maxexptime = 1.3,
+		minsize = 1.5,
+		maxsize = 3.5,
+		texture = "nether_particle_anim4.png",
+		animation = {
+			type = "vertical_frames",
+			aspect_w = 7,
+			aspect_h = 7,
+			length = 1.4,
+		}
+	})
+
+	if node.name == "nether:lava_source" or node.name == "nether:lava_crust" then
+		-- use swap_node to avoid triggering the lava_crust's after_destruct
+		minetest.swap_node(pos, {name = "nether:basalt"})
+
+		minetest.sound_play("default_cool_lava",
+			{pos = pos, max_hear_distance = 16, gain = 0.25}, true)
+	else
+		-- chain the original ABM action to handle conventional lava
+		original_cool_lava_action(pos, node)
+	end
+end
+
+
+minetest.register_on_mods_loaded(function()
+
+	-- register a bucket of Lava-sea source - but make it just the same bucket as default lava.
+	-- (by doing this in register_on_mods_loaded we don't need to declare a soft dependency)
+	if minetest.get_modpath("bucket") and minetest.global_exists("bucket") and type(bucket.liquids) == "table" then
+		local lava_bucket = bucket.liquids["default:lava_source"]
+		if lava_bucket ~= nil then
+			local lavasea_bucket = {}
+			for key, value in pairs(lava_bucket) do lavasea_bucket[key] = value end
+			lavasea_bucket.source = "nether:lava_source"
+			bucket.liquids[lavasea_bucket.source] = lavasea_bucket
+		end
+	end
+
+	-- include "nether:lava_source" in any "default:lava_source" ABMs
+	local function include_nether_lava(set_of_nodes)
+		if (type(set_of_nodes) == "table") then
+			for _, nodename in pairs(set_of_nodes) do
+				if nodename == "default:lava_source" then
+					-- I'm amazed this works, but it does
+					table.insert(set_of_nodes, "nether:lava_source")
+					break;
+				end
+			end
+		end
+	end
+
+	for _, abm in pairs(minetest.registered_abms) do
+		include_nether_lava(abm.nodenames)
+		include_nether_lava(abm.neighbors)
+		if abm.label == "Lava cooling" and abm.action ~= nil then
+			-- lets have lava_crust cool as well
+			original_cool_lava_action = abm.action
+			abm.action = nether.cool_lava
+			table.insert(abm.nodenames, "nether:lava_crust")
+		end
+	end
+	for _, lbm in pairs(minetest.registered_lbms) do
+		include_nether_lava(lbm.nodenames)
+	end
+	--minetest.log("minetest.registered_abms" .. dump(minetest.registered_abms))
+	--minetest.log("minetest.registered_lbms" .. dump(minetest.registered_lbms))
+end)
+
+-- creates a lava splash, and leaves lava_source in place of the lava_crust
+local function smash_lava_crust(pos, playsound)
+
+	local lava_particlespawn_def = {
+		amount = 6,
+		time = 0.1,
+		minpos = {x=pos.x - 0.5, y=pos.y + 0.3, z=pos.z - 0.5},
+		maxpos = {x=pos.x + 0.5, y=pos.y + 0.5, z=pos.z + 0.5},
+		minvel = {x = -1.5, y = 1.5, z = -1.5},
+		maxvel = {x =  1.5, y = 5,   z =  1.5},
+		minacc = {x = 0, y = -10, z = 0},
+		maxacc = {x = 0, y = -10, z = 0},
+		minexptime = 1,
+		maxexptime = 1,
+		minsize = .2,
+		maxsize = .8,
+		texture = "^[colorize:#A00:255",
+		glow = 8
+	}
+	minetest.add_particlespawner(lava_particlespawn_def)
+	lava_particlespawn_def.texture = "^[colorize:#FB0:255"
+	lava_particlespawn_def.maxvel.y = 3
+	lava_particlespawn_def.glow = 12
+	minetest.add_particlespawner(lava_particlespawn_def)
+
+	minetest.set_node(pos, {name = "default:lava_source"})
+
+	if math.random(1, 3) == 1 and minetest.registered_nodes["fire:basic_flame"] ~= nil then
+		-- occasionally brief flames will be seen when breaking lava crust
+		local posAbove = {x = pos.x, y = pos.y + 1, z = pos.z}
+		if minetest.get_node(posAbove).name == "air" then
+			minetest.set_node(posAbove, {name = "fire:basic_flame"})
+			minetest.get_node_timer(posAbove):set(math.random(7, 15) / 10, 0)
+			--[[ commented out because the flame sound plays for too long
+			if minetest.global_exists("fire") and fire.update_player_sound ~= nil then
+				-- The fire mod only updates its sound every 3 seconds, these flames will be
+				-- out by then, so start the sound immediately
+				local players = minetest.get_connected_players()
+				for n = 1, #players do fire.update_player_sound(players[n]) end
+			end]]
+		end
+	end
+
+	if playsound then
+		minetest.sound_play(
+			"nether_lava_bubble",
+			-- this sample was encoded at 3x speed to reduce .ogg file size
+			-- at the expense of higher frequencies, so pitch it down ~3x
+			{pos = pos, pitch = 0.3, max_hear_distance = 8, gain = 0.4}
+		)
+	end
+end
+
+
+-- lava_crust nodes can only be used in the biomes-based mapgen, since they require
+-- the MT 5.0 world-align texture features.
+minetest.register_node("nether:lava_crust", {
+	description = S("Lava Crust"),
+	_doc_items_longdesc = S("A thin crust of cooled lava with liquid lava beneath"),
+	_doc_items_usagehelp = S("Lava crust is strong enough to walk on, but still hot enough to inflict burns."),
+	tiles = {
+		{
+			name="nether_lava_crust_animated.png",
+			backface_culling=true,
+			tileable_vertical=true,
+			tileable_horizontal=true,
+			align_style="world",
+			scale=2,
+			animation = {
+				type = "vertical_frames",
+				aspect_w = 32,
+				aspect_h = 32,
+				length = 1.8,
+			},
+		}
+	},
+	inventory_image = minetest.inventorycube(
+		"nether_lava_crust_animated.png^[sheet:2x48:0,0",
+		"nether_lava_crust_animated.png^[sheet:2x48:0,1",
+		"nether_lava_crust_animated.png^[sheet:2x48:1,1"
+	),
+	collision_box = {
+		type = "fixed",
+		fixed = {
+			-- Damage is calculated "starting 0.1 above feet
+			-- and progressing upwards in 1 node intervals", so
+			-- lower this node's collision box by more than 0.1
+			-- to ensure damage will be taken when standing on
+			-- the node.
+			{-0.5, -0.5, -0.5, 0.5, 0.39, 0.5}
+		},
+	},
+	selection_box = {
+		type = "fixed",
+		fixed = {
+			-- Keep the selection box matching the visual node,
+			-- rather than the collision_box.
+			{-0.5, -0.5, -0.5, 0.5, 0.5, 0.5}
+		},
+	},
+
+	after_destruct = function(pos, oldnode)
+		smash_lava_crust(pos, true)
+	end,
+	after_dig_node = function(pos, oldnode, oldmetadata, digger)
+	end,
+	on_blast = function(pos, intensity)
+		smash_lava_crust(pos, false)
+	end,
+
+	paramtype = "light",
+	light_source = default.LIGHT_MAX - 3,
+	buildable_to = false,
+	walkable = true,
+	is_ground_content = true,
+	drop = {
+		items = {{
+			-- Allow SilkTouch-esque "pickaxes of preservation" to mine the lava crust intact, if PR #10141 gets merged.
+			tools = {"this line will block early MT versions which don't respect the tool_groups restrictions"},
+			tool_groups = {{"pickaxe", "preservation"}},
+			items = {"nether:lava_crust"}
+		}}
+	},
+	--liquid_viscosity = 7,
+	damage_per_second = 2,
+	groups = {oddly_breakable_by_hand = 3, cracky = 3, explody = 1, igniter = 1},
+})
+
+
+-- Fumaroles (Chimney's)
+
+local function fumarole_startTimer(pos, timeout_factor)
+
+	if timeout_factor == nil then timeout_factor = 1 end
+	local next_timeout = (math.random(50, 900) / 10) * timeout_factor
+
+	minetest.get_meta(pos):set_float("expected_timeout", next_timeout)
+	minetest.get_node_timer(pos):start(next_timeout)
+end
+
+-- Create an LBM to start fumarole node timers
+minetest.register_lbm({
+	label = "Start fumarole smoke",
+	name  = "nether:start_fumarole",
+	nodenames = {"nether:fumarole"},
+	run_at_every_load = true,
+	action = function(pos, node)
+		local node_above = minetest.get_node({x = pos.x, y = pos.y + 1, z = pos.z})
+		if node_above.name == "air" then --and node.param2 % 4 == 0 then
+			fumarole_startTimer(pos)
+		end
+	end
+})
+
+local function set_fire(pos, extinguish)
+	local posBelow  = {x = pos.x, y = pos.y - 1, z = pos.z}
+
+	if extinguish then
+		if minetest.get_node(pos).name      == "fire:permanent_flame" then minetest.set_node(pos,      {name="air"}) end
+		if minetest.get_node(posBelow).name == "fire:permanent_flame" then minetest.set_node(posBelow, {name="air"}) end
+
+	elseif minetest.get_node(posBelow).name == "air" then
+		minetest.set_node(posBelow, {name="fire:permanent_flame"})
+	elseif minetest.get_node(pos).name == "air" then
+		minetest.set_node(pos, {name="fire:permanent_flame"})
+	end
+end
+
+local function fumarole_onTimer(pos, elapsed)
+
+	local expected_timeout = minetest.get_meta(pos):get_float("expected_timeout")
+	if elapsed > expected_timeout + 10 then
+		-- The timer didn't fire when it was supposed to, so the chunk was probably inactive and has
+		-- just been approached again, meaning *every* fumarole's on_timer is about to go off.
+		-- Skip this event and restart the clock for a future random interval.
+		fumarole_startTimer(pos, 1)
+		return false
+	end
+
+	-- Fumaroles in the Nether can catch fire.
+	-- (if taken to the surface and used as cottage chimneys, they don't catch fire)
+	local inNether = pos.y <= nether.DEPTH and pos.y >= nether.DEPTH_FLOOR_LAYERS
+	local canCatchFire = inNether and minetest.registered_nodes["fire:permanent_flame"] ~= nil
+	local smoke_offset   = 0
+	local timeout_factor = 1
+	local smoke_time_adj = 1
+
+	local posAbove = {x = pos.x, y = pos.y + 1, z = pos.z}
+	local extinguish = minetest.get_node(posAbove).name ~= "air"
+
+	if extinguish or (canCatchFire and math.floor(elapsed) % 7 == 0) then
+
+		if not extinguish then
+			-- fumarole gasses are igniting
+			smoke_offset   = 1
+			timeout_factor = 0.22 -- reduce burning time
+		end
+
+		set_fire(posAbove, extinguish)
+		set_fire({x = pos.x + 1, y = pos.y + 1, z = pos.z},     extinguish)
+		set_fire({x = pos.x - 1, y = pos.y + 1, z = pos.z},     extinguish)
+		set_fire({x = pos.x,     y = pos.y + 1, z = pos.z + 1}, extinguish)
+		set_fire({x = pos.x,     y = pos.y + 1, z = pos.z - 1}, extinguish)
+
+	elseif inNether then
+
+		if math.floor(elapsed) % 3 == 1 then
+			-- throw up some embers / lava splash
+			local embers_particlespawn_def = {
+				amount = 6,
+				time = 0.1,
+				minpos = {x=pos.x - 0.1, y=pos.y + 0.0, z=pos.z - 0.1},
+				maxpos = {x=pos.x + 0.1, y=pos.y + 0.2, z=pos.z + 0.1},
+				minvel = {x = -.5, y = 4.5, z = -.5},
+				maxvel = {x =  .5, y = 7,   z =  .5},
+				minacc = {x = 0, y = -10, z = 0},
+				maxacc = {x = 0, y = -10, z = 0},
+				minexptime = 1.4,
+				maxexptime = 1.4,
+				minsize = .2,
+				maxsize = .8,
+				texture = "^[colorize:#A00:255",
+				glow = 8
+			}
+			minetest.add_particlespawner(embers_particlespawn_def)
+			embers_particlespawn_def.texture = "^[colorize:#A50:255"
+			embers_particlespawn_def.maxvel.y = 3
+			embers_particlespawn_def.glow = 12
+			minetest.add_particlespawner(embers_particlespawn_def)
+
+		else
+			-- gas noises
+			minetest.sound_play("nether_fumarole", {
+				pos = pos,
+				max_hear_distance = 60,
+				gain = 0.24,
+				pitch = math.random(35, 95) / 100
+			})
+		end
+
+	else
+		-- we're not in the Nether, so can afford to be a bit more smokey
+		timeout_factor = 0.4
+		smoke_time_adj = 1.3
+	end
+
+	-- let out some smoke
+	minetest.add_particlespawner({
+		amount = 12 * smoke_time_adj,
+		time = math.random(40, 60) / 10 * smoke_time_adj,
+		minpos = {x=pos.x - 0.2, y=pos.y + smoke_offset, z=pos.z - 0.2},
+		maxpos = {x=pos.x + 0.2, y=pos.y + smoke_offset, z=pos.z + 0.2},
+		minvel = {x=0, y=0.7, z=-0},
+		maxvel = {x=0, y=0.8, z=-0},
+		minacc = {x=0.0,y=0.0,z=-0},
+		maxacc = {x=0.0,y=0.1,z=-0},
+		minexptime = 5,
+		maxexptime = 5.5,
+		minsize = 1.5,
+		maxsize = 7,
+		texture = "nether_smoke_puff.png",
+	})
+
+	fumarole_startTimer(pos, timeout_factor)
+	return false
+end
+
+
+minetest.register_node("nether:fumarole", {
+	description=S("Fumarolic Chimney"),
+	_doc_items_longdesc = S("A vent in the earth emitting steam and gas"),
+	_doc_items_usagehelp = S("Can be repurposed to provide puffs of smoke in a chimney"),
+	tiles = {"nether_rack.png"},
+	on_timer = fumarole_onTimer,
+	after_place_node = function(pos, placer, itemstack, pointed_thing)
+		fumarole_onTimer(pos, 1)
+		return false
+	end,
+	is_ground_content = true,
+	groups = {cracky = 3, level = 2, fumarole=1},
+	paramtype = "light",
+	drawtype = "nodebox",
+	node_box = {
+		type = "fixed",
+		fixed = {
+			{-0.5000, -0.5000, -0.5000, -0.2500, 0.5000, 0.5000},
+			{-0.5000, -0.5000, -0.5000, 0.5000, 0.5000, -0.2500},
+			{-0.5000, -0.5000, 0.2500, 0.5000, 0.5000, 0.5000},
+			{0.2500, -0.5000, -0.5000, 0.5000, 0.5000, 0.5000}
+		}
+	},
+	selection_box = {type = 'fixed', fixed = {-.5, -.5, -.5, .5, .5, .5}}
+})
+
+minetest.register_node("nether:fumarole_slab", {
+	description=S("Fumarolic Chimney Slab"),
+	_doc_items_longdesc = S("A vent in the earth emitting steam and gas"),
+	_doc_items_usagehelp = S("Can be repurposed to provide puffs of smoke in a chimney"),
+	tiles = {"nether_rack.png"},
+	is_ground_content = true,
+	on_timer = fumarole_onTimer,
+	after_place_node = function(pos, placer, itemstack, pointed_thing)
+		fumarole_onTimer(pos, 1)
+		return false
+	end,
+	groups = {cracky = 3, level = 2, fumarole=1},
+	paramtype = "light",
+	drawtype = "nodebox",
+	node_box = {
+		type = "fixed",
+		fixed = {
+			{-0.5000, -0.5000, -0.5000, -0.2500, 0.000, 0.5000},
+			{-0.5000, -0.5000, -0.5000, 0.5000, 0.000, -0.2500},
+			{-0.5000, -0.5000, 0.2500, 0.5000, 0.000, 0.5000},
+			{0.2500, -0.5000, -0.5000, 0.5000, 0.000, 0.5000}
+		}
+	},
+	selection_box = {type = 'fixed', fixed = {-.5, -.5, -.5, .5, 0, .5}},
+	collision_box = {type = 'fixed', fixed = {-.5, -.5, -.5, .5, 0, .5}}
+})
+
+minetest.register_node("nether:fumarole_corner", {
+	description=S("Fumarolic Chimney Corner"),
+	tiles = {"nether_rack.png"},
+	is_ground_content = true,
+	groups = {cracky = 3, level = 2, fumarole=1},
+	paramtype = "light",
+	paramtype2 = "facedir",
+	drawtype = "nodebox",
+	node_box = {
+		type = "fixed",
+		fixed = {
+			{-0.2500, -0.5000, 0.5000, 0.000, 0.5000, 0.000},
+			{-0.5000, -0.5000, 0.2500, 0.000, 0.5000, 0.000},
+			{-0.5000, -0.5000, 0.2500, 0.000, 0.000, -0.5000},
+			{0.000, -0.5000, -0.5000, 0.5000, 0.000, 0.5000}
+		}
+	},
+	selection_box = {
+		type = 'fixed',
+		fixed = {
+			{-.5, -.5, -.5, .5, 0, .5},
+			{0, 0, .5, -.5, .5, 0},
+		}
+	}
+
+})
+
+-- nether:airlike_darkness is an air node through which light does not propagate.
+-- Use of it should be avoided when possible as it has the appearance of a lighting bug.
+-- Fumarole decorations use it to stop the propagation of light from the lava below,
+-- since engine limitations mean any mesh or nodebox node will light up if it has lava
+-- below it.
+local airlike_darkness = {}
+for k,v in pairs(minetest.registered_nodes["air"]) do airlike_darkness[k] = v end
+airlike_darkness.paramtype = "none"
+minetest.register_node("nether:airlike_darkness", airlike_darkness)

portal_api.lua

@@ -1780,7 +1780,7 @@ local function create_book_of_portals()
 		ignition_item_description = minetest.registered_items[ignition_item_name].description
 	end
 	intro_text = intro_text ..
-		S("\n\nThe key to opening such a doorway is to strike the frame with a @1, at which point the very air inside begins to crackle and glow.", string.lower(ignition_item_description))
+		S("\n\nThe key to opening such a doorway is to strike the frame with a @1, at which point the very air inside begins to crackle and glow.", ignition_item_description)
 
 	chapters[#chapters + 1] = {text = intro_text}
 
@@ -2007,7 +2007,8 @@ local wormhole_nodedef_default = {
 		a = 160, r = 128, g = 0, b = 80
 	},
 	sunlight_propagates = true,
-	use_texture_alpha = true,
+	use_texture_alpha = minetest.features.use_texture_alpha_string_modes
+		and "blend" or true,
 	walkable = false,
 	diggable = false,
 	pointable = false,
@@ -2015,7 +2016,6 @@ local wormhole_nodedef_default = {
 	is_ground_content = false,
 	drop = "",
 	light_source = 5,
-	alpha = 192,
 	node_box = {
 		type = "fixed",
 		fixed = {
@@ -2073,7 +2073,7 @@ function nether.register_portal(name, portaldef)
 	end
 
 	portaldef.name     = name
-	portaldef.mod_name = minetest.get_current_modname()
+	portaldef.mod_name = minetest.get_current_modname() or "<mod name not recorded>"
 
 	-- use portaldef_default for any values missing from portaldef or portaldef.sounds
 	if portaldef.sounds ~= nil then setmetatable(portaldef.sounds, {__index = portaldef_default.sounds}) end
@@ -2211,7 +2211,7 @@ function nether.volume_is_natural_and_unprotected(minp, maxp, player_name)
 			if id ~= c_air and id ~= c_ignore and id ~= nil then -- checked for common natural or not emerged
 				local name = minetest.get_name_from_content_id(id)
 				local nodedef = minetest.registered_nodes[name]
-				if not nodedef.is_ground_content then
+				if nodedef and not nodedef.is_ground_content then
 					-- trees are natural but not "ground content"
 					local node_groups = nodedef.groups
 					if node_groups == nil or (node_groups.tree == nil and node_groups.leaves == nil and node_groups.leafdecay == nil) then
@@ -2388,4 +2388,4 @@ function nether.find_nearest_working_portal(portal_name, anchorPos, distance_lim
 		end
 	end
 	return nil
-end
+end

portal_api.txt

@@ -22,6 +22,9 @@ one kind of portal with the same frame material — such as obsidian — provide
 the size of the PortalShape is distinct from any other type of portal that is
 using the same node for its frame, and portal sizes remain small.
 
+The Nether provides three variants of Nether basalt to ensure there are
+alternatives to obsidian for other mods to use as portalstones.
+
 
 Realms
 ------
@@ -247,16 +250,16 @@ Used by `nether.register_portal`.
         -- player_name may be "", e.g. if the portal was ignited by a mesecon,
         -- and is provided for use with volume_is_natural_and_unprotected() etc.
 
-        on_run_wormhole      = function(portalDef, anochorPos, orientation),
+        on_run_wormhole      = function(portalDef, anchorPos, orientation),
         -- invoked once per second per portal
-        on_extinguish        = function(portalDef, anochorPos, orientation),
+        on_extinguish        = function(portalDef, anchorPos, orientation),
         -- invoked when a portal is extinguished, including when the portal
         -- it connected to was extinguished.
         on_player_teleported = function(portalDef, player, oldPos, newPos),
         -- invoked immediately after a player is teleported
-        on_ignite            = function(portalDef, anochorPos, orientation)
+        on_ignite            = function(portalDef, anchorPos, orientation)
         -- invoked when a player or mesecon ignites a portal
-        on_created           = function(portalDef, anochorPos, orientation)
+        on_created           = function(portalDef, anchorPos, orientation)
         -- invoked when a portal creates a remote twin, this is usually when
         -- a player travels through a portal for the first time.
     }

portal_examples.lua

@@ -106,7 +106,7 @@ end
 -- Surface-travel portal, playable code example --
 --==============================================--
 
--- These Moore Curve functions requred by surface_portal's find_surface_anchorPos() will
+-- These Moore Curve functions required by surface_portal's find_surface_anchorPos() will
 -- be assigned later in this file.
 local get_moore_distance -- will be function get_moore_distance(cell_count, x, y): integer
 local get_moore_coords   -- will be function get_moore_coords(cell_count, distance): pos2d

tools.lua

@@ -0,0 +1,138 @@
+--[[
+
+  Copyright (C) 2020 lortas
+
+  Permission to use, copy, modify, and/or distribute this software for
+  any purpose with or without fee is hereby granted, provided that the
+  above copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+  WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR
+  BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES
+  OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+  WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+  ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+  SOFTWARE.
+
+]]--
+
+local S = nether.get_translator
+
+minetest.register_tool("nether:pick_nether", {
+	description = S("Nether Pickaxe"),
+	inventory_image = "nether_tool_netherpick.png",
+	tool_capabilities = {
+		full_punch_interval = 0.8,
+		max_drop_level=3,
+		groupcaps={
+			cracky = {times={[1]=1.90, [2]=0.9, [3]=0.4}, uses=35, maxlevel=3},
+		},
+		damage_groups = {fleshy=4},
+	},
+	sound = {breaks = "default_tool_breaks"},
+	groups = {pickaxe = 1}
+})
+
+minetest.register_tool("nether:shovel_nether", {
+	description = S("Nether Shovel"),
+	inventory_image = "nether_tool_nethershovel.png",
+	wield_image = "nether_tool_nethershovel.png^[transformR90",
+	tool_capabilities = {
+		full_punch_interval = 1.0,
+		max_drop_level=3,
+		groupcaps={
+			crumbly = {times={[1]=1.0, [2]=0.4, [3]=0.25}, uses=35, maxlevel=3},
+		},
+		damage_groups = {fleshy=4},
+	},
+	sound = {breaks = "default_tool_breaks"},
+	groups = {shovel = 1}
+})
+
+minetest.register_tool("nether:axe_nether", {
+	description = S("Nether Axe"),
+	inventory_image = "nether_tool_netheraxe.png",
+	tool_capabilities = {
+		full_punch_interval = 0.8,
+		max_drop_level=1,
+		groupcaps={
+			choppy={times={[1]=1.9, [2]=0.7, [3]=0.4}, uses=35, maxlevel=3},
+		},
+		damage_groups = {fleshy=7},
+	},
+	sound = {breaks = "default_tool_breaks"},
+	groups = {axe = 1}
+})
+
+minetest.register_tool("nether:sword_nether", {
+	description = S("Nether Sword"),
+	inventory_image = "nether_tool_nethersword.png",
+	tool_capabilities = {
+		full_punch_interval = 0.7,
+		max_drop_level=1,
+		groupcaps={
+			snappy={times={[1]=1.5, [2]=0.6, [3]=0.2}, uses=45, maxlevel=3},
+		},
+		damage_groups = {fleshy=10},
+	},
+	sound = {breaks = "default_tool_breaks"},
+	groups = {sword = 1}
+})
+
+minetest.register_craftitem("nether:nether_ingot", {
+	description = S("Nether Ingot"),
+	inventory_image = "nether_nether_ingot.png"
+})
+minetest.register_craftitem("nether:nether_lump", {
+	description = S("Nether Lump"),
+	inventory_image = "nether_nether_lump.png",
+})
+
+minetest.register_craft({
+	type = "cooking",
+	output = "nether:nether_ingot",
+	recipe = "nether:nether_lump",
+	cooktime = 30,
+})
+minetest.register_craft({
+	output = "nether:nether_lump",
+	recipe = {
+		{"nether:brick_compressed","nether:brick_compressed","nether:brick_compressed"},
+		{"nether:brick_compressed","nether:brick_compressed","nether:brick_compressed"},
+		{"nether:brick_compressed","nether:brick_compressed","nether:brick_compressed"},
+	}
+})
+
+minetest.register_craft({
+	output = "nether:pick_nether",
+	recipe = {
+		{"nether:nether_ingot","nether:nether_ingot","nether:nether_ingot"},
+		{"", "group:stick", ""},
+		{"", "group:stick", ""}
+	}
+})
+minetest.register_craft({
+	output = "nether:shovel_nether",
+	recipe = {
+		{"nether:nether_ingot"},
+		{"group:stick"},
+		{"group:stick"}
+	}
+})
+minetest.register_craft({
+	output = "nether:axe_nether",
+	recipe = {
+		{"nether:nether_ingot","nether:nether_ingot"},
+		{"nether:nether_ingot","group:stick"},
+		{"","group:stick"}
+	}
+})
+minetest.register_craft({
+	output = "nether:sword_nether",
+	recipe = {
+		{"nether:nether_ingot"},
+		{"nether:nether_ingot"},
+		{"group:stick"}
+	}
+})