Add biome generation in engine

Currently, performance seems an issue - the cause of the effects is to be determined.

API.md

@@ -126,6 +126,12 @@ The biomes are defined as follows:
     node_roof = "foo:bluestone",
     -- Node forming the ceiling of the cave
 
+    node_air = "foo:air",
+    -- Nodes filling the inside of the cave. By default, this is air.
+    -- You can replace it with e.g. water to make the entire cave a water cave.
+    -- Keep in mind that cave biomes can blend, so it might not always look
+    -- very smooth.
+
     node_shell = "foo:permafrost",
     depth_shell = 3,
     -- Node forming a layer around the entire cave and thickness of this layer

init.lua

@@ -11,6 +11,9 @@ noordstar_caves = {}
 -- Load features to influence cave shapes
 load("shape")
 
+-- Load features to influence cave biomes
+load("biome")
+
 -- Start engine to generate caves
 load("engine")
 

lua/biome.lua

@@ -59,6 +59,9 @@ local function clean_def(def)
     if type(def.node_roof) == "string" then
         d.node_roof = def.node_roof
     end
+    if type(def.node_air) == "string" then
+        d.node_air = def.node_air
+    end
     if type(def.node_shell) == "string" then
         d.node_shell = def.node_shell
     end

lua/engine.lua

@@ -2,6 +2,38 @@
 -- Constants and magic numbers
 local mapgen_buffer = 16
 
+-- Noise params for heat_point
+local heat_noise_params =
+    { offset = 50
+    , scale = 50
+    , spread = { x = 200, y = 200, z = 200 }
+    , seed = 320523
+    , octaves = 2
+    , persistence = 0.1
+    , lacunarity = 2.0
+    , flags = ""
+    }
+
+-- Noise params for humidity_point
+local humidity_noise_params =
+    { offset = 50
+    , scale = 50
+    , spread = { x = 200, y = 200, z = 200 }
+    , seed = 9923473
+    , octaves = 2
+    , persistence = 0.1
+    , lacunarity = 2.0
+    , flags = ""
+    }
+
+local default_biome =
+    { name = "noordstar_caves:none"
+    , heat_point = -1e6
+    , humidity_point = -1e6
+    , minp = { x = -1e5, y = -1e5, z = -1e5 }
+    , maxp = { x =  1e5, y =  1e5, z =  1e5 }
+    }
+
 -- Convert 3d relative coordinates to an index on a flat array
 local function from_3d_to_flat(dx, dy, dz, nx, ny)
     return (nx * ny * dz) + (nx * dy) + dx + 1
@@ -421,6 +453,46 @@ local function get_flat_cave_node_types(minp, maxp)
     end)
 end
 
+-- Transform categorized blocks into 
+local function biome_def_to_content_id(def, nt, original_block)
+    local function get_node(name, alt)
+        return function()
+            if name == nil then
+                return alt
+            else
+                return minetest.get_content_id(name)
+            end
+        end
+    end
+
+    local node_air     = get_node(def.node_air, minetest.get_content_id("air"))
+    local node_floor   = get_node(def.node_floor, original_block)
+    local node_stone   = original_block
+    local node_roof    = get_node(def.node_roof, original_block)
+    local node_unknown = original_block
+    local node_wall    = get_node(def.node_wall, original_block)
+
+    if nt == node_type.unknown then
+        return node_unknown
+    elseif nt == node_type.floor then
+        return node_floor()
+    elseif nt == node_type.wall then
+        return node_wall()
+    elseif nt == node_type.roof then
+        return node_roof()
+    elseif nt == node_type.content then
+        return node_air()
+    elseif nt == node_type.stone then
+        return node_stone
+    else
+        return original_block
+    end
+end
+
+local function biome_distance(def, heat, humidity)
+    return (def.heat_point - heat)^2 + (def.humidity_point - humidity)^2
+end
+
 minetest.register_on_generated(function(minp, maxp, blockseed)
     local vminp =
         { x = minp.x - mapgen_buffer
@@ -440,29 +512,35 @@ minetest.register_on_generated(function(minp, maxp, blockseed)
     -- Get threshold values
     local node_types = get_flat_cave_node_types(vminp, vmaxp)
     
-    local node_air   = minetest.get_content_id("air")
-    local node_floor = minetest.get_content_id("mcl_core:glass_green")
-    local node_wall  = minetest.get_content_id("mcl_core:glass_purple")
-    local node_roof  = minetest.get_content_id("mcl_core:glass_red")
-    local node_other = minetest.get_content_id("mcl_core:glass")
+    local heat_points = get_flat_from_noise_params(minp, maxp, heat_noise_params)
+    local humidity_points = get_flat_from_noise_params(minp, maxp, humidity_noise_params)
 
+    -- Map block values
     local nids = Flat3dArray:from_func(vminp, vmaxp, function(i, pos)
         local nt = node_types:get_pos(pos)
 
         if not is_valid_pos(pos, minp, maxp) then
             return flat_data:get_pos(pos)
-        elseif nt == node_type.unknown then
-            return node_other
-        elseif nt == node_type.floor then
-            return node_floor
-        elseif nt == node_type.wall then
-            return node_wall
-        elseif nt == node_type.roof then
-            return node_roof
-        elseif nt == node_type.content then
-            return node_air
-        elseif nt == node_type.stone then
-            return flat_data:get_pos(pos)
+        else
+            local biome = default_biome
+
+            local heat = heat_points:get_pos(pos)
+            local humidity = humidity_points:get_pos(pos)
+
+            for _, def in pairs(noordstar_caves.registered_biomes) do
+                if pos.x < def.minp.x then
+                elseif pos.y < def.minp.y then
+                elseif pos.z < def.minp.z then
+                elseif pos.x > def.maxp.x then
+                elseif pos.y > def.maxp.y then
+                elseif pos.z > def.maxp.z then
+                elseif biome_distance(def, heat, humidity) > biome_distance(biome, heat, humidity) then
+                else
+                    biome = def
+                end
+            end
+
+            return biome_def_to_content_id(biome, nt, flat_data:get_pos(pos))
         end
     end)