1 files changed, 59 insertions, 0 deletions
diff --git a/src/rtw/perlin.zig b/src/rtw/perlin.zig
new file mode 100644
index 0000000..df5de76
--- /dev/null
+++ b/src/rtw/perlin.zig
@@ -0,0 +1,59 @@
+const rand = @import("rand.zig");
+const Random = rand.Random;
+const randomReal01 = rand.randomReal01;
+const randomInt = rand.randomInt;
+const Point3 = @import("vec.zig").Point3;
+
+pub const Perlin = struct {
+    const POINT_COUNT = 256;
+
+    randomNoise: [POINT_COUNT]f64,
+    permX: [POINT_COUNT]usize,
+    permY: [POINT_COUNT]usize,
+    permZ: [POINT_COUNT]usize,
+
+    pub fn init(rng: Random) Perlin {
+        var perlin = Perlin{
+            .randomNoise = undefined,
+            .permX = undefined,
+            .permY = undefined,
+            .permZ = undefined,
+        };
+
+        var i: usize = 0;
+        while (i < POINT_COUNT) : (i += 1) {
+            perlin.randomNoise[i] = randomReal01(rng);
+        }
+        perlinGeneratePerm(rng, &perlin.permX);
+        perlinGeneratePerm(rng, &perlin.permY);
+        perlinGeneratePerm(rng, &perlin.permZ);
+
+        return perlin;
+    }
+
+    pub fn noise(perlin: Perlin, p: Point3) f64 {
+        const i = @intCast(usize, @floatToInt(i32, 4.0 * p.x) & 255);
+        const j = @intCast(usize, @floatToInt(i32, 4.0 * p.y) & 255);
+        const k = @intCast(usize, @floatToInt(i32, 4.0 * p.z) & 255);
+
+        return perlin.randomNoise[perlin.permX[i] ^ perlin.permY[j] ^ perlin.permZ[k]];
+    }
+
+    fn perlinGeneratePerm(rng: Random, p: []usize) void {
+        var i: usize = 0;
+        while (i < POINT_COUNT) : (i += 1) {
+            p[i] = i;
+        }
+        permute(rng, p, POINT_COUNT);
+    }
+
+    fn permute(rng: Random, p: []usize, n: usize) void {
+        var i = n - 1;
+        while (i > 0) : (i -= 1) {
+            const target = randomInt(usize, rng, 0, i);
+            const tmp = p[i];
+            p[i] = p[target];
+            p[target] = tmp;
+        }
+    }
+};