mandelbrot

Commit: 630121998c5f85b2bb1b4e5d8058ad618a5047e7
Parent: 0cbf3890a22657b5bb305ac0fa513eae16613c05
Author: Randy Palamar
Date:   Fri, 24 May 2024 21:15:14 -0600

try to use escape count as a wavelength for colours

Diffstat:
M
frag.glsl
 | 
82
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------------

1 file changed, 69 insertions(+), 13 deletions(-)
diff --git a/frag.glsl b/frag.glsl
@@ -5,30 +5,86 @@ out vec4 colour;
 
 uniform uvec2 u_screen_dim;
 
-vec2 map_mandelbrot(vec2 v)
+vec2 map_mandelbrot(vec2 v, float aspect)
 {
-	float x = v.x * 2.47 - 2;
-	float y = v.y * 2.14 - 1.12;
-	return vec2(x, y);
+	/* midpoint is (-0.765, 0) */
+	/* x is in [-2.00, 0.47] */
+	/* x new [-2.5, 1] -> 3.5 */
+	/* y is in [-1.12, 1.12]  */
+	/* y new [-1.5, 1.5] -> 3.0 */
+	vec2 delta = vec2(0);
+
+	float desired_aspect = 3.5 / 3;
+	delta.x = -0.765 - 3.5 * desired_aspect / 2;
+	delta.y = -1.5;
+
+	float x = v.x * 3.5 * desired_aspect;
+	float y = v.y * 3;
+	return vec2(x, y) + delta;
+}
+
+vec3 wavelength2rgb(float lambda)
+{
+	vec3 rgb = vec3(0);
+	float t;
+	/* red */
+	if        (lambda >= 400 && lambda < 410) {
+		t = (lambda - 400) / 10;
+		rgb.x =        0.33 * t - (0.20 * t * t);
+	} else if (lambda >= 410 && lambda < 475) {
+		t = (lambda - 410) / 65;
+		rgb.x = 0.14            - (0.13 * t * t);
+	} else if (lambda >= 545 && lambda < 595) {
+		t = (lambda - 545) / 50;
+		rgb.x =        1.98 * t - (      t * t);
+	} else if (lambda >= 595 && lambda < 650) {
+		t = (lambda - 595) / 65;
+		rgb.x = 0.98 + 0.06 * t - (0.40 * t * t);
+	} else if (lambda >= 650 && lambda < 700) {
+		t = (lambda - 650) / 50;
+		rgb.x = 0.65 - 0.84 * t + (0.20 * t * t);
+	}
+
+	/* green */
+	if        (lambda >= 415 && lambda < 475) {
+		t = (lambda - 415) / 60;
+		rgb.y =                 + (0.80 * t * t);
+	} else if (lambda >= 475 && lambda < 585) {
+		t = (lambda - 475) / 115;
+		rgb.y = 0.80 + 0.76 * t - (0.80 * t * t);
+	} else if (lambda >= 585 && lambda < 639) {
+		t = (lambda - 585) / 54;
+		rgb.y = 0.84 - 0.84 * t                 ;
+	}
+
+	/* blue */
+	if        (lambda >= 400 && lambda < 475) {
+		t = (lambda - 400) / 75;
+		rgb.z =        2.20 * t - (1.50 * t * t);
+	} else if (lambda >= 475 && lambda < 560) {
+		t = (lambda - 475) / 85;
+		rgb.z = 0.70 +        t + (0.30 * t * t);
+	}
+	return rgb;
 }
 
 void main()
 {
-	vec2 xy0 = map_mandelbrot(gl_FragCoord.xy / u_screen_dim.xy);
-	colour = vec4(0, 0, 0.1, 1);
+	float aspect = u_screen_dim.x / u_screen_dim.y;
+	vec2 xy0 = map_mandelbrot(gl_FragCoord.xy / u_screen_dim.xy, aspect);
 
 	int i;
 	float xx = 0, yy = 0;
 	vec2 xy  = xy0;
-	for (i = 0; i < 256 && xx + yy < 4.0; i++) {
+	for (i = 0; i < 300 && xx + yy < 15.0; i++) {
 		xx = xy.x * xy.x;
 		yy = xy.y * xy.y;
 		xy = vec2(xx - yy + xy0.x, 2 * xy.x * xy.y + xy0.y);
 	}
-	if (i < 256) {
-		float r = (i >> 0) / 255.0;
-		float g = (i >> 2) / 255.0;
-		float b = (i >> 3) / 255.0;
-		colour = vec4(r, g, b, 1.0);
-	}
+
+	float mu = i - log(log(sqrt(xx + yy))) / log(2.0);
+	mu = clamp(mu, 0, 300);
+	//float q = pow(mu / 300, 0.2);
+	float q = mu / 300;
+	colour = vec4(wavelength2rgb(400.0 + 300 * q).xyz, 1.0);
 }