Reign-in the default on-generated limit from +/- 31k to -16/+48m

since nothing much is normally found outside that range anyway

only enqueue blocks that are within that range, or within
the range specfied by all of the mods that make generate_plant() calls,
whichever covers more volume.

API.txt

@@ -112,9 +112,9 @@ biome = {
 	depth_max = num,	-- If the object spawns on top of a water source, the
 						-- water must be at most this deep.  Defaults to 1.
 	min_elevation = num, -- Surface must be at this altitude or higher to
-						-- spawn at all.  Defaults to -31000...
+						 -- spawn at all.  Defaults to -16 meters.
-	max_elevation = num, -- ...but must be no higher than this altitude.
+	max_elevation = num, -- Surface must be no higher than this altitude.
-						-- Defaults to +31000.
+						 -- Defaults to +48.
 	near_nodes = {table}, -- List of nodes that must be somewhere in the
 						-- vicinity in order for the plant to spawn. Can also
 						-- be a string with a single node name.  If not
@@ -270,8 +270,8 @@ biome = {
 	depth = num,		-- How deep/thick of a layer the spawned-on node must
 						-- be.  Typically used for water.
 	min_elevation = num, -- Minimum elevation in meters/nodes.  Defaults to
-						-- -31000 (unlimited).
+						-- -16 meters.
-	max_elevation = num, -- Max elevation.  Defaults to +31000 (unlimited).
+	max_elevation = num, -- Max elevation.  Defaults to +48m.
 	near_nodes = {table}, -- what nodes must be in the general vicinity of the
 						-- object being spawned.
 	near_nodes_size = num, -- how wide of a search area to look for the nodes

init.lua

@@ -33,6 +33,10 @@ biome_lib.actionslist_no_aircheck = {}
 biome_lib.surfaceslist_aircheck = {}
 biome_lib.surfaceslist_no_aircheck = {}
 
+-- the mapgen rarely creates useful surfaces outside this range, but mods can
+-- still specify a wider range if needed.
+biome_lib.mapgen_elevation_limit = { ["min"] = -16, ["max"] = 48 } 
+
 biome_lib.modpath = minetest.get_modpath("biome_lib")
 
 local function tableize(s)
@@ -153,8 +157,8 @@ end
 
 function biome_lib:set_defaults(biome)
 	biome.seed_diff = biome.seed_diff or 0
-	biome.min_elevation = biome.min_elevation or -31000
+	biome.min_elevation = biome.min_elevation or biome_lib.mapgen_elevation_limit.min
-	biome.max_elevation = biome.max_elevation or 31000
+	biome.max_elevation = biome.max_elevation or biome_lib.mapgen_elevation_limit.max
 	biome.temp_min = biome.temp_min or 1
 	biome.temp_max = biome.temp_max or -1
 	biome.humidity_min = biome.humidity_min or 1
@@ -206,6 +210,9 @@ function biome_lib:register_generate_plant(biomedef, nodes_or_function_or_model)
 		biome_lib.dbg("Warning: Registered function call using deprecated string method: "..dump(nodes_or_function_or_model), 2)
 	end
 
+	biome_lib.mapgen_elevation_limit.min = math.min(biomedef.min_elevation or 0, biome_lib.mapgen_elevation_limit.min)
+	biome_lib.mapgen_elevation_limit.max = math.max(biomedef.max_elevation or 0, biome_lib.mapgen_elevation_limit.max)
+
 	if biomedef.check_air == false then 
 		biome_lib.dbg("Register no-air-check mapgen hook: "..dump(nodes_or_function_or_model), 3)
 		biome_lib.actionslist_no_aircheck[#biome_lib.actionslist_no_aircheck + 1] = { biomedef, nodes_or_function_or_model }
@@ -859,6 +866,8 @@ end
 minetest.after(0, function()
 	biome_lib.dbg("Registered a total of "..(#biome_lib.surfaceslist_aircheck)+(#biome_lib.surfaceslist_no_aircheck).." surface types to be evaluated, spread", 0)
 	biome_lib.dbg("across "..#biome_lib.actionslist_aircheck.." actions with air-checking and "..#biome_lib.actionslist_no_aircheck.." actions without.", 0)
+	biome_lib.dbg("within an elevation range of "..biome_lib.mapgen_elevation_limit.min.." and "..biome_lib.mapgen_elevation_limit.max.." meters.", 0)
+
 end)
 
 biome_lib.dbg("[Biome Lib] Loaded", 0)

search_functions.lua

@@ -57,10 +57,15 @@ end
 
 minetest.register_on_generated(function(minp, maxp, blockseed)
 	local timestamp = minetest.get_us_time()
-	for x = 0, 4 do
-		local minx = minp.x + x*16
 	for y = 0, 4 do
 		local miny = minp.y + y*16
+
+		if miny >= biome_lib.mapgen_elevation_limit.min
+		  and (miny + 15) <= biome_lib.mapgen_elevation_limit.max then
+
+			for x = 0, 4 do
+				local minx = minp.x + x*16
+
 				for z = 0, 4 do
 					local minz = minp.z + z*16
 
@@ -70,6 +75,9 @@ minetest.register_on_generated(function(minp, maxp, blockseed)
 					biome_lib.block_log[#biome_lib.block_log + 1] = { bmin, bmax, false, timestamp }
 				end
 			end
+		else
+			biome_lib.dbg("Did not enqueue mapblocks at elevation "..miny.."m, they're out of range of any generate_plant() calls.", 4)
+		end
 	end
 	biome_lib.run_block_recheck_list = true
 end)