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.

init.lua

@@ -76,6 +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.
@@ -163,7 +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 =
@@ -188,7 +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 =
@@ -253,12 +266,12 @@ The expedition parties have found no diamonds or gold, and after an experienced
 				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 getRegion(),
-					-- so only use getRegion() if it exists
-					if nether.mapgen.getRegion ~= nil then
+					-- 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.getRegion(pos)
+						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

mapgen.lua

@@ -81,7 +81,8 @@ local math_max, math_min, math_abs, math_floor = math.max, math.min, math.abs, m
 
 -- Inject nether_caverns biome
 
-local function override_underground_biomes()
+-- 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
@@ -124,21 +125,21 @@ local function override_underground_biomes()
 		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 new_y_min, new_y_max
-			local spaceOccupiedAbove = biome_y_max - NETHER_CEILING
-			local spaceOccupiedBelow = NETHER_FLOOR - biome_y_min
+			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_y_min = NETHER_CEILING + 1
-				new_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_y_max = NETHER_FLOOR - 1
-				new_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)
@@ -162,7 +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.
@@ -259,12 +260,12 @@ mapgen.np_cave = {
 
 local cavePointPerlin = nil
 
-mapgen.getCavePointPerlin = function()
+mapgen.get_cave_point_perlin = function()
 	cavePointPerlin = cavePointPerlin or minetest.get_perlin(mapgen.np_cave)
 	return cavePointPerlin
 end
 
-mapgen.getCavePerlinAt = function(pos)
+mapgen.get_cave_perlin_at = function(pos)
 	cavePointPerlin = cavePointPerlin or minetest.get_perlin(mapgen.np_cave)
 	return cavePointPerlin:get_3d(pos)
 end
@@ -477,7 +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 = mapgen.getCavePointPerlin()
+	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")

mapgen_mantle.lua

@@ -119,7 +119,7 @@ mapgen.add_basalt_columns = function(data, area, minp, maxp)
 	local yStride = area.ystride
 	local yCaveStride = x1 - x0 + 1
 
-	local cavePerlin = mapgen.getCavePointPerlin()
+	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)
 
@@ -431,13 +431,13 @@ mapgen.RegionEnum = {
 
 -- Returns (region, noise) where region is a value from mapgen.RegionEnum
 -- and noise is the unadjusted cave perlin value
-mapgen.getRegion = function(pos)
+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.getCavePerlinAt(pos)
+	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
@@ -482,7 +482,7 @@ minetest.register_chatcommand("nether_whereami",
 			if player == nil then return false, S("Unknown player position") end
 			local playerPos = vector.round(player:get_pos())
 
-			local region, caveNoise                = mapgen.getRegion(playerPos)
+			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)
 

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

@@ -337,7 +337,7 @@ nether.cool_lava = function(pos, node)
 	-- 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 then
+		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"})
@@ -604,7 +604,7 @@ local function fumarole_onTimer(pos, elapsed)
 
 	-- 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
+	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

portal_api.lua

@@ -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

portal_api.txt

@@ -250,16 +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