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learning/random/print_chr.frag

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+#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 random (in vec2 _st) {
+  return fract(sin(dot(_st.xy, vec2(12.9898, 78.233))));
+}
+
+vec2 truchetPattern(in vec2 _st, in float _index) {
+  _index = fract(((_index-.5)*2.));
+  if (_index > .75) {
+    _st = vec2(1.0) - _st;
+   } else if (_index > .5) {
+     _st = vec2(1.0-_st.x, _st.y);
+   } else if (_index > .25) {
+     _st = 1.0-vec2(1.0-_st.x, _st.y);
+   }
+  return _st;
+}
+
+void main() {
+  //vec2 st = (gl_FragCoord.xy*2. - u_resolution.xy)/u_resolution.y;
+  vec2 st = (gl_FragCoord.xy / u_resolution.xy);
+  st *= 10.;
+  vec3 color = vec3(0.0,0.0,0.0);
+  float alpha = 1.0;
+  // st = (st-vec2(5.))*(abs(sin(u_time*.2))*5.);
+  // st.x += u_time*3.;
+
+  vec2 ipos = floor(st);
+  vec2 fpos = fract(st);
+
+
+  vec2 tile = truchetPattern(fpos, random(ipos));
+
+  color += smoothstep(tile.x-.3,tile.x,tile.y)-smoothstep(tile.x,tile.x+0.3,tile.y);
+  
+
+  gl_FragColor = vec4(color, alpha);
+}