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);
+}