
  var program = webglUtils.createProgramFromSources(gl,
      [vertexShaderSource, fragmentShaderSource]);

  // look up where the vertex data needs to go.
  var positionAttributeLocation = gl.getAttribLocation(program, "a_position");

  // look up uniform locations
  var colorLocation = gl.getUniformLocation(program, "u_color");
  var matrixLocation = gl.getUniformLocation(program, "u_matrix");

  // Create a buffer
  var positionBuffer = gl.createBuffer();

  // Create a vertex array object (attribute st