add math.noise2d

res/modules/internal/extensions/math.lua

@@ -71,3 +71,49 @@ function math.noise(x, octaves)
     end
     return value
 end
+
+local function lerp(a, b, t)
+    return a + (b - a) * t
+end
+
+local function rand_2d(x, y)
+    return noise_rands[math.floor(x * 317 + y) % noise_period + 1]
+end
+
+local function sample_noise2d(x, y)
+    local x0 = math.floor(x)
+    local y0 = math.floor(y)
+    local x1 = x0 + 1
+    local y1 = y0 + 1
+
+    local tx = x - x0
+    local ty = y - y0
+
+    local sx = smoothstep(tx)
+    local sy = smoothstep(ty)
+
+    local c00 = rand_2d(x0, y0)
+    local c10 = rand_2d(x1, y0)
+    local c01 = rand_2d(x0, y1)
+    local c11 = rand_2d(x1, y1)
+
+    local bottom = lerp(c00, c10, sx)
+    local top = lerp(c01, c11, sx)
+
+    return lerp(bottom, top, sy)
+end
+
+
+function math.noise2d(x, y, octaves)
+    octaves = octaves or 1
+    local value = 0.0
+    local mul = 1.0
+    for i=1,octaves do
+        value = value * (1.0 - mul)
+            + sample_noise2d(x + 37 * i, y + 73 * i) * mul
+        x = x * 2.0
+        y = y * 2.0
+        mul = mul * 0.5
+    end
+    return value
+end