Remove mcl_structures:structblocks (#4619)

As spawning happens via gennotify anyway, we can omit placing a
structblock right away.

This also avoids certain cases of holes in snow cover or water.
Plus, the code is simpler.

Isolated from the big mapgen overhaul, for the main branch.

Reviewed-on: https://git.minetest.land/VoxeLibre/VoxeLibre/pulls/4619
Reviewed-by: Mikita Wiśniewski <rudzik8@protonmail.com>
Co-authored-by: kno10 <erich.schubert@gmail.com>
Co-committed-by: kno10 <erich.schubert@gmail.com>

mods/MAPGEN/mcl_mapgen_core/init.lua

@@ -484,18 +484,14 @@ end
 -- This should be moved to mcl_structures eventually if the dependencies can be sorted out.
 mcl_mapgen_core.register_generator("structures",nil, function(minp, maxp, blockseed)
 	local gennotify = minetest.get_mapgen_object("gennotify")
-	local has_struct = {}
 	local has = false
 	local poshash = minetest.hash_node_position(minp)
 	for _,struct in pairs(mcl_structures.registered_structures) do
 		local pr = PseudoRandom(blockseed + 42)
 		if struct.deco_id then
 			for _, pos in pairs(gennotify["decoration#"..struct.deco_id] or {}) do
-				local realpos = vector.offset(pos,0,1,0)
-				minetest.remove_node(realpos)
-				minetest.fix_light(vector.offset(pos,-1,-1,-1),vector.offset(pos,1,3,1))
 				if struct.chunk_probability == nil or (not has and pr:next(1,struct.chunk_probability) == 1 ) then
-					mcl_structures.place_structure(realpos,struct,pr,blockseed)
+					mcl_structures.place_structure(vector.offset(pos,0,1,0),struct,pr,blockseed)
 					has=true
 				end
 			end

mods/MAPGEN/mcl_structures/api.lua

@@ -325,24 +325,18 @@ function mcl_structures.place_structure(pos, def, pr, blockseed, rot)
 	end
 end
 
-function mcl_structures.register_structure(name,def,nospawn) --nospawn means it will be placed by another (non-nospawn) structure that contains it's structblock i.e. it will not be placed by mapgen directly
+local EMPTY_SCHEMATIC = { size = {x = 0, y = 0, z = 0}, data = { } }
+
+function mcl_structures.register_structure(name,def,nospawn) --nospawn means it will not be placed by mapgen decoration mechanism
 	if mcl_structures.is_disabled(name) then return end
-	local structblock = "mcl_structures:structblock_"..name
+	flags = def.flags or "place_center_x, place_center_z, force_placement"
-	local flags = "place_center_x, place_center_z, force_placement"
-	local y_offset = 0
-	local sbgroups = { structblock = 1, not_in_creative_inventory=1 }
-	if def.flags then flags = def.flags end
 	def.name = name
-	if nospawn then
+	if not nospawn and def.place_on then
-		sbgroups.structblock = nil
-		sbgroups.structblock_lbm = 1
-	else
-		if def.place_on then
 		minetest.register_on_mods_loaded(function() --make sure all previous decorations and biomes have been registered
 			def.deco = minetest.register_decoration({
 				name = "mcl_structures:deco_"..name,
-					decoration = structblock,
+				deco_type = "schematic",
-					deco_type = "simple",
+				schematic = EMPTY_SCHEMATIC,
 				place_on = def.place_on,
 				spawn_by = def.spawn_by,
 				num_spawn_by = def.num_spawn_by,
@@ -354,15 +348,11 @@ function mcl_structures.register_structure(name,def,nospawn) --nospawn means it
 				y_max = def.y_max,
 				y_min = def.y_min
 			})
-				minetest.register_node(":"..structblock, {drawtype="airlike", walkable = false, pointable = false,groups = sbgroups,sunlight_propagates = true,})
-				def.structblock = structblock
 			def.deco_id = minetest.get_decoration_id("mcl_structures:deco_"..name)
 			minetest.set_gen_notify({decoration=true}, { def.deco_id })
 			--catching of gennotify happens in mcl_mapgen_core
-
 		end)
 	end
-	end
 	mcl_structures.registered_structures[name] = def
 end
 
@@ -395,16 +385,4 @@ function mcl_structures.register_structure_spawn(def)
 	})
 end
 
---lbm for secondary structures (structblock included in base structure)
+
-minetest.register_lbm({
-	name = "mcl_structures:struct_lbm",
-	run_at_every_load = true,
-	nodenames = {"group:structblock_lbm"},
-	action = function(pos, node)
-		minetest.remove_node(pos)
-		local name = node.name:gsub("mcl_structures:structblock_","")
-		local def = mcl_structures.registered_structures[name]
-		if not def then return end
-		mcl_structures.place_structure(pos)
-	end
-})