a more reasonable temperature range to START from

src/main.lua

@@ -3,11 +3,14 @@ math.randomseed(os.time())
 local map_generator = require "map_nextgen"
 local lovebird = require "lib.lovebird"
 local lume = require "lib.lume"
+local simplex_map = require "lib.simplex_map"
 
 local map
 
 love.load = function()
   map = map_generator.generate()
+  map.temperature.min = simplex_map.min(map.temperature)
+  map.temperature.max = simplex_map.max(map.temperature)
   print("Temperature Range", map.temperature.min, map.temperature.max)
 
   -- if true then return end
@@ -73,7 +76,7 @@ love.draw = function()
       local value = map.temperature[x][y]
       if value then
         -- love.graphics.setColor(value)
-        love.graphics.setColor( (value + 89.2) / (89.2 + 56.7) , 0, 0, 1)
+        love.graphics.setColor( (value + map.temperature.max) / (map.temperature.max + math.abs(map.temperature.min)) , 0, 0, 1)
         love.graphics.rectangle("fill", x * map.tile_size, y * map.tile_size, map.tile_size, map.tile_size)
       end
     end

src/map_nextgen.lua

@@ -1,75 +1,7 @@
 -- NOTE the API of this file should probably change?
 
 local lume = require "lib.lume"
-local simplex = require "lib.simplex"
+local simplex_map = require "lib.simplex_map"
-
-local simplex_map = {}
-
-simplex_map.min = function(map)
-  local r = map[1][1]
-  for i=1,#map do
-    for j=1,#map[1] do
-      if r > map[i][j] then r = map[i][j] end
-    end
-  end
-  return r
-end
-simplex_map.max = function(map)
-  local r = map[1][1]
-  for i=1,#map do
-    for j=1,#map[1] do
-      if r < map[i][j] then r = map[i][j] end
-    end
-  end
-  return r
-end
-
-simplex_map.normalize = function(map, new_min, new_max)
-  local minimum = simplex_map.min(map)
-  local initialRange = simplex_map.max(map) - minimum
-  local finalRange = new_max - new_min
-  for i = 1, #map do
-    for j = 1, #map[1] do
-      map[i][j] = (map[i][j] - minimum) / initialRange * finalRange + new_min
-    end
-  end
-  map.min = simplex_map.min(map)
-  map.max = simplex_map.max(map)
-  return map -- superfluous
-end
-
-simplex_map.generate = function(size, scale, min, max, octaves, lacunarity, gain)
-  if type(size) == "table" then
-    scale = size.scale
-    min = size.min
-    max = size.max
-    octaves = size.octaves
-    lacunarity = size.lacunarity
-    gain = size.gain
-
-    size = size.size
-  end
-
-  simplex.Seed(math.random())
-  local map = {}
-  map.size = size
-
-  scale = scale or 0.005
-  for x = 1, map.size do
-    map[x] = {}
-    for y = 1, map.size do
-      map[x][y] = simplex.FractalBrownianMotion2D(x * scale, y * scale, octaves, lacunarity, gain)
-    end
-  end
-
-  if min or max then
-    min = min or 0
-    max = max or 1
-    simplex_map.normalize(map, min, max)
-  end
-
-  return map
-end
 
 local biomes = {
   -- biomes are checked in order, with the first candidate always being selected
@@ -126,7 +58,8 @@ local generate = function()
     octaves = 7, lacunarity = 2, gain = 0.5,
   }
   map.temperature = simplex_map.generate{   -- in celsius
-    size = map.size, scale = 0.005, min = -89.2, max = 56.7,
+    -- -20 to 45 chosen by looking at the temperature range shown on https://openclimatemap.org/
+    size = map.size, scale = 0.005, min = -20, max = 45, -- approximate target extremes of -89.2 to 56.7
     octaves = 1, lacunarity = 2, gain = 0.5,
   }
   map.rainfall = simplex_map.generate{   -- in millimeters of rainfall
@@ -159,13 +92,23 @@ local generate = function()
     map.biome[x] = {}
     for y = 1, map.size do
       if lume.distance(x, y, map.size / 2, map.size / 2, true) < radius_squared then
+        local altitude = map.altitude[x][y]
+        local temperature = map.temperature[x][y]
+        local rainfall = map.rainfall[x][y]
+
+        -- modify temperature based on altitude
+        if altitude > 0 then
+          temperature = temperature - 0.0065 * altitude  -- -6.5 C / km
+        else
+          temperature = temperature + altitude / 1000 -- -1 C / km (deep water adjustment)
+        end
+        map.temperature[x][y] = temperature
+
+        -- choose biome
         for _, order in ipairs(biome_order) do
           local biome = biomes[order]
-          local altitude = map.altitude[x][y]
           if altitude >= biome.altitude.min and altitude <= biome.altitude.max then
-            local temperature = map.temperature[x][y]
             if temperature >= biome.temperature.min and temperature <= biome.temperature.max then
-              local rainfall = map.rainfall[x][y]
               if rainfall >= biome.rainfall.min and rainfall <= biome.rainfall.max then
                 map.biome[x][y] = biome.color
                 break