basic: added distance field example; utils: added polygon shape drawer

basic/distance_field.glsl

@@ -0,0 +1,21 @@
+#ifdef GL_ES
+precision mediump float;
+#endif
+
+uniform vec2 u_resolution;
+
+void main(){
+  vec2 st = gl_FragCoord.xy/u_resolution.xy;
+  st.x *= u_resolution.x/u_resolution.y;
+  vec3 color = vec3(0.0);
+  float d = 0.0;
+
+  // Remap the space to -1. to 1.
+  st = st *2.-1.;
+
+  // Make the distance field
+  d = length(st)+length(min(st,0.))+length(max(st,0.));
+
+  // Visualize the distance field
+  gl_FragColor = vec4(vec3(fract(d*10.0)),1.0);
+}

utilities/shapes.glsl

@@ -4,3 +4,19 @@ vec3 circle(in vec2 _st, in float _radius, vec3 color){
                          _radius+(_radius*0.02),
                          dot(dist,dist)*4.0);
 }
+
+// Inspired by (but modified)
+// http://thndl.com/square-shaped-shaders.html
+#define TAU 6.28318530718
+vec3 polygon(int n, float size, vec2 pos, vec3 color, float rot) {
+  float e = 0.01;
+  vec2 st = gl_FragCoord.xy/u_resolution.xy;
+  st.x *= u_resolution.x/u_resolution.y;
+  st = (st-pos)*2.;
+  float a = atan(st.x,st.y)+rot;
+  float r = TAU/float(n);
+
+  float d = cos(floor(.5+a/r)*r-a)*length(st);
+
+  return color-smoothstep(size-e,size+e,d);
+}