ik versta da met de polar coordinats nu denk ik

learning/PixelSpirit/the_devil.frag

@@ -0,0 +1,45 @@
+#ifdef GL_ES
+precision mediump float;
+#endif
+uniform vec2 u_resolution;
+uniform vec2 u_mouse;
+uniform float u_time;
+
+#define PI 3.14159265359
+
+const vec3 uAColor = vec3(.5,.5,.5);
+const vec3 uBColor = vec3(.5,.5,.5);
+const vec3 uCColor = vec3(1.,1.,1.);
+const vec3 uDColor = vec3(.0,.33,.67);
+
+//get colors from http://dev.thi.ng/gradients/
+vec3 cosPalette(float t) { return uAColor + uBColor*cos(6.28318*(uCColor*t+uDColor)); }
+
+float starSDF(vec2 st, int V, float s) {
+  st = st*4.-2.;
+  float a = atan(st.y, st.x)/(2.*PI);
+  float seg = a * float(V);
+  a = ((floor(seg) + .5)/float(V)+mix(s,-s,step(.5,fract(seg))))*(2.*PI);
+  return abs(dot(vec2(cos(a),sin(a)),st));
+}
+
+float stroke(in float x_coor, float s, float width){
+  float d = step(s,x_coor+width*.5)-step(s,x_coor-width*.5);
+  return clamp(d, 0.,1.);
+}
+
+float circleSDF(vec2 st) { return length(st-.5)*2.; }
+
+void main() {
+  vec2 st = gl_FragCoord.xy/u_resolution;
+  vec3 color = vec3(0.0,0.0,0.0);
+  float alpha = 1.0;
+  color += stroke(circleSDF(st),.8,.05);
+  st.y = 1.-st.y;
+  float s = starSDF(st.yx,5,.1);
+  color *= step(.7,s);
+  color += stroke(s,.4,.1);
+  
+
+  gl_FragColor = vec4(color, alpha);
+}