));
  
  vec2 uv = vec2(a, r);

  gl_FragColor = texture2D(tex, uv);
}
`;

var gl = document.querySelector("canvas").getContext("webgl");
var programInfo1 = twgl.createProgramInfo(gl, [vs, fs1]);
var programInfo2 = twgl.createProgramInfo(gl, [vs, fs2]);
var bufferInfo = twgl.createBufferInfoFromArrays(gl, {
  position: {
    numComponents: 2,
    data: [
      -1, -1, 
       1, -1,
      -1,  1,
      -1,  1,
       1, -1,
       1,  1,
    ],
  },
});
      
var texture = twgl.createTexture(gl, { 
  src: 