attribute vec4 a_Position;
attribute float a_PointSize;
void main(){
  gl_Position = a_Position;
  gl_PointSize = a_PointSize;
}

precision mediump float;
uniform float u_Width;
uniform float u_Height;
void main(){
  gl_FragColor = vec4(gl_FragCoord.x/u_Width, gl_FragCoord.y/u_Height, gl_FragCoord.z/u_Height, 1.0);
}