Increasing maxInterations glsl100 to 255 to match with glsl330 and add glsl120

examples/shaders/resources/shaders/glsl100/julia_set.fs

@@ -12,7 +12,7 @@ uniform float zoom;             // Zoom of the scale.
 
 // NOTE: Maximum number of shader for-loop iterations depend on GPU,
 // for example, on RasperryPi for this examply only supports up to 60
-const int maxIterations = 48;     // Max iterations to do.
+const int maxIterations = 255;     // Max iterations to do.
 const float colorCycles = 1.0;    // Number of times the color palette repeats.
 
 // Square a complex number
@@ -57,7 +57,7 @@ void main()
     z.y += offset.y;
 
     int iter = 0;
-    for (int iterations = 0; iterations < 60; iterations++)
+    for (int iterations = 0; iterations < maxIterations; iterations++)
     {
         z = ComplexSquare(z) + c;  // Iterate function
         if (dot(z, z) > 4.0) break;

examples/shaders/resources/shaders/glsl120/julia_set.fs

@@ -0,0 +1,80 @@
+#version 120
+
+// Input vertex attributes (from vertex shader)
+varying vec2 fragTexCoord;
+varying vec4 fragColor;
+
+uniform vec2 c;                 // c.x = real, c.y = imaginary component. Equation done is z^2 + c
+uniform vec2 offset;            // Offset of the scale.
+uniform float zoom;             // Zoom of the scale.
+
+// NOTE: Maximum number of shader for-loop iterations depend on GPU,
+// for example, on RasperryPi for this examply only supports up to 60
+const int maxIterations = 255;     // Max iterations to do.
+const float colorCycles = 1.0;    // Number of times the color palette repeats.
+
+// Square a complex number
+vec2 ComplexSquare(vec2 z)
+{
+    return vec2(z.x*z.x - z.y*z.y, z.x*z.y*2.0);
+}
+
+// Convert Hue Saturation Value (HSV) color into RGB
+vec3 Hsv2rgb(vec3 c)
+{
+    vec4 K = vec4(1.0, 2.0/3.0, 1.0/3.0, 3.0);
+    vec3 p = abs(fract(c.xxx + K.xyz)*6.0 - K.www);
+    return c.z*mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
+}
+
+void main()
+{
+    /**********************************************************************************************
+      Julia sets use a function z^2 + c, where c is a constant.
+      This function is iterated until the nature of the point is determined.
+
+      If the magnitude of the number becomes greater than 2, then from that point onward
+      the number will get bigger and bigger, and will never get smaller (tends towards infinity).
+      2^2 = 4, 4^2 = 8 and so on.
+      So at 2 we stop iterating.
+
+      If the number is below 2, we keep iterating.
+      But when do we stop iterating if the number is always below 2 (it converges)?
+      That is what maxIterations is for.
+      Then we can divide the iterations by the maxIterations value to get a normalized value that we can
+      then map to a color.
+
+      We use dot product (z.x * z.x + z.y * z.y) to determine the magnitude (length) squared.
+      And once the magnitude squared is > 4, then magnitude > 2 is also true (saves computational power).
+    *************************************************************************************************/
+
+    // The pixel coordinates are scaled so they are on the mandelbrot scale
+    // NOTE: fragTexCoord already comes as normalized screen coordinates but offset must be normalized before scaling and zoom
+    vec2 z = vec2((fragTexCoord.x - 0.5)*2.5, (fragTexCoord.y - 0.5)*1.5)/zoom;
+    z.x += offset.x;
+    z.y += offset.y;
+
+    int iter = 0;
+    for (int iterations = 0; iterations < maxIterations; iterations++)
+    {
+        z = ComplexSquare(z) + c;  // Iterate function
+        if (dot(z, z) > 4.0) break;
+
+        iter = iterations;
+    }
+
+    // Another few iterations decreases errors in the smoothing calculation.
+    // See http://linas.org/art-gallery/escape/escape.html for more information.
+    z = ComplexSquare(z) + c;
+    z = ComplexSquare(z) + c;
+
+    // This last part smooths the color (again see link above).
+    float smoothVal = float(iter) + 1.0 - (log(log(length(z)))/log(2.0));
+
+    // Normalize the value so it is between 0 and 1.
+    float norm = smoothVal/float(maxIterations);
+
+    // If in set, color black. 0.999 allows for some float accuracy error.
+    if (norm > 0.999) gl_FragColor = vec4(0.0, 0.0, 0.0, 1.0);
+    else gl_FragColor = vec4(Hsv2rgb(vec3(norm*colorCycles, 1.0, 1.0)), 1.0);
+}