text: varying lowp vec3 vColor;
  varying mediump vec2 vTexCoord;
  varying mediump float vFog;
  
  void main(void) {
  	lowp float d = dot(vTexCoord, vTexCoord);
  	lowp float w = clamp(1.0 - 9.0 * d, 0.0, 1.0);
  	gl_FragColor = clamp(vec4(vColor + vec3(w), (1.0 - d)*1.125 * vFog), 0.0, 1.0);
  }
  
  