Allow reignition of portals in player-built areas

e.g. allow remote ignition to a portal in a "portal room"

init.lua

@@ -25,7 +25,7 @@
 local NETHER_DEPTH = -5000
 local TCAVE = 0.6
 local BLEND = 128
-local DEBUG = true
+local DEBUG = false
 
 
 -- 3D noise
@@ -77,14 +77,15 @@ netherportal = {} -- portal API
 A better location for AnchorPos would be directly under WormholePos, as it's more centered
 and you don't need to know the portal's orientation to find AnchorPos from the WormholePos
 or vice-versa, however AnchorPos is in the bottom/south/west-corner to keep compatibility
-with earlier versions of this mod (which only records portal corners p1 & p2 in the node metadata).
+with earlier versions of nether mod (which only records portal corners p1 & p2 in the node 
+metadata).
 
 Orientation is 0 or 90, 0 meaning a portal that faces north/south - i.e. obsidian running
 east/west.
 ]]
 
 
--- This object defines a portal's shape, segregating the shape logic code from portal physics.
+-- This object defines a portal's shape, segregating the shape logic code from portal behaviour code.
 -- You can create a new "PortalShape" definition object which implements the same
 -- functions if you wish to register a custom shaped portal in register_portal().
 -- Since it's symmetric, this PortalShape definition has only implemented orientations of 0 and 90
@@ -294,8 +295,9 @@ local function set_portal_metadata(portal_definition, anchorPos, orientation, de
 		meta:set_string("target",          minetest.pos_to_string(destination_wormholePos))
 		-- including "frame_node_name" in the metadata lets us know which kind of portal this is.
 		-- It's not strictly necessary for TraditionalPortalShape as we know that p1 is part of
-		-- the frame, and legacy portals don't have this extra metadata, but p1 isn't always loaded
+		-- the frame, and legacy portals don't have this extra metadata - indicating obsidian, 
-		-- and reading this from the metadata saves an extra call to minetest.getnode().
+		-- but p1 isn't always loaded so reading this from the metadata saves an extra call to 
+		-- minetest.getnode().
 		meta:set_string("frame_node_name", portal_definition.frame_node_name)
 	end
 
@@ -515,13 +517,20 @@ Also, the search for non-natural nodes doesn't actually guarantee avoiding playe
 Each placement position search has to search a volume of nodes for non-natural nodes, this is not lightweight, and many searches may happen if there a lot of underground player builds present. So the code has been written to avoid intensive procedures.
 https://github.com/minetest-mods/nether/issues/5#issuecomment-506983676
 ]]
-local function find_surface_target_y(target_x, target_z, start_y)
+local function find_surface_target_y(portal_definition, target_x, target_z, start_y)
 	for y = start_y, start_y - 256, -16 do
 		-- Check volume for non-natural nodes
 		local minp = {x = target_x - 1, y = y - 1, z = target_z - 2}
 		local maxp = {x = target_x + 2, y = y + 3, z = target_z + 2}
 		if volume_is_natural(minp, maxp) then
 			return y
+		else
+			-- players have built here - don't grief.
+			-- but reigniting existing portals in portal rooms is fine - desirable even.
+			local anchorPos, orientation, is_ignited = is_portal_frame(portal_definition, {x = target_x, y = y, z = target_z})
+			if anchorPos ~= nil then
+				return y
+			end
 		end
 	end
 
@@ -557,7 +566,7 @@ local function ignite_portal(ignition_pos)
 	-- pick a destination
 	local destination_wormholePos = portal_definition.shape.get_wormholePos_from_anchorPos(anchorPos, orientation)
 	if anchorPos.y < NETHER_DEPTH then
-		destination_wormholePos.y = find_surface_target_y(destination_wormholePos.x, destination_wormholePos.z, -16)
+		destination_wormholePos.y = find_surface_target_y(portal_definition, destination_wormholePos.x, destination_wormholePos.z, -16)
 	else
 		local start_y = NETHER_DEPTH - math.random(500, 1500) -- Search start
 		destination_wormholePos.y = find_nether_target_y(destination_wormholePos.x, destination_wormholePos.z, start_y)
@@ -776,7 +785,7 @@ minetest.register_lbm({
 	nodenames = {"nether:portal"},
 	run_at_every_load = false,
 	action = function(pos, node)
-		local p1
+		local p1, p2
 		local meta = minetest.get_meta(pos)
 		if meta ~= nil then
 			p1 = minetest.string_to_pos(meta:get_string("p1"))