First attempt for mandelbrot implementation

src/fractal.frag

@@ -2,6 +2,94 @@
 
 layout (location = 0) out vec4 color;
 
-void main() {
-    color = vec4(1.0, 0.0, 0.0, 1.0);
+const int MAX_ITER = 1000;
+const float SIZE = 0.01;
+
+float hue_to_rgb(float p, float q, float t) {
+	if (t < 0.0) {
+		t += 1.0;
+	}
+
+	if (t > 1.0) {
+		t -= 1.0;
+	}
+
+	if (t < (1.0 / 6.0)) {
+		return p + (q - p) * 6.0 * t;
+	} else if (t < (1.0 / 2.0)) {
+		return q;
+	} else if (t < (2.0 / 3.0)) {
+		return p + (q - p) * (2.0 / 3.0 - t) * 6.0;
+	}
+
+	return p;
+}
+
+vec3 hsl_to_rgb(float h, float s, float l) {
+	float r, g, b;
+
+	if (s == 0.0) {
+		r = l;
+		g = l;
+		b = l;
+	} else {
+		float q, p;
+
+		if (l < 0.5) {
+			q = l * (1. + s);
+		} else {
+			q = l + s - l * s;
+		}
+
+		p = 2. * l - q;
+		r = hue_to_rgb(p, q, h + 1.0 / 3.0);
+		g = hue_to_rgb(p, q, h);
+		b = hue_to_rgb(p, q, h - 1.0 / 3.0);
+	}
+
+	return vec3(r, g, b);
+}
+
+void mandelbrot_iter(float px, float py, out float ox, out int iter) {
+    float x = 0.0;
+    float y = 0.0;
+    float xx = 0.0;
+    float yy = 0.0;
+    float xy = 0.0;
+
+    for (int i = 0; i < MAX_ITER; i++) {
+        xx = x * x;
+        yy = y * y;
+        xy = x * y;
+
+        if ((xx + yy) > 4.0) {
+            ox = xx + yy;
+            iter = i;
+
+            return;
+        }
+
+        x = xx - yy + px;
+        y = 2.0 * xy + py;
+    }
+
+    ox = xx + yy;
+    iter = MAX_ITER;
+}
+
+vec3 paint(float nx, float ny) {
+    float r;
+    int n;
+
+    mandelbrot_iter(SIZE * nx, SIZE * ny, r, n);
+
+    if (r > 4.0) {
+        return hsl_to_rgb(float(n) / 800.0 * r, 1.0, 0.5);
+    } else {
+        return vec3(1.0, 1.0, 1.0);
+    }
+}
+
+void main() {
+    color = vec4(paint(gl_FragCoord.x, gl_FragCoord.y), 1.0);
 }