Add mandelbrot example (#34)

example/mandelbrot.glsl

@@ -0,0 +1,51 @@
+// Source: https://github.com/Erkaman/vulkan_minimal_compute/blob/master/shaders/shader.comp
+layout (local_size_x = 32, local_size_y = 32, local_size_z = 1) in;
+
+layout(binding = 0) buffer buf
+{
+   vec4 imageData[];
+};
+
+void main() {
+
+  /*
+  In order to fit the work into workgroups, some unnecessary threads are launched.
+  We terminate those threads here. 
+  */
+  //if(gl_GlobalInvocationID.x >= 3200 || gl_GlobalInvocationID.y >= 2400)
+  //  return;
+
+  float x = float(gl_GlobalInvocationID.x) / float(3200);
+  float y = float(gl_GlobalInvocationID.y) / float(2400);
+
+  /*
+  What follows is code for rendering the mandelbrot set. 
+  */
+  vec2 uv = vec2(x, y);
+  float n = 0.0;
+  float _calc = 2.0 + 1.7 * 0.2;
+  vec2 c = vec2(-.445, 0.0) + (uv - vec2(0.5, 0.5)) * vec2(_calc, _calc);
+  vec2 z = vec2(0.0, 0.0);
+  int M = 128;
+
+  for (int i = 0; i < M; ++i) {
+    z = vec2(z.x * z.x - z.y * z.y, 2. * z.x * z.y) + c;
+
+    if (int(dot(z, z)) > 2)
+      break;
+
+    n = n + 1.0;
+  }
+
+  // we use a simple cosine palette to determine color:
+  // http://iquilezles.org/www/articles/palettes/palettes.htm         
+  float t = float(n) / float(128);
+  vec3 d = vec3(0.3, 0.3, 0.5);
+  vec3 e = vec3(-0.2, -0.3 ,-0.5);
+  vec3 f = vec3(2.1, 2.0, 3.0);
+  vec3 g = vec3(0.0, 0.1, 0.0);
+  vec4 color = vec4(d + e * cos(vec3(6.28318, 6.28318, 6.28318) *(f * vec3(t, t, t) + g)), 1.0);
+
+  // store the rendered mandelbrot set into a storage buffer:
+  imageData[3200u * gl_GlobalInvocationID.y + gl_GlobalInvocationID.x] = color;
+}