text: // RotatedTranslatedTriangle.js (c) 2012 matsuda
  // Vertex shader program
  var VSHADER_SOURCE =
    'attribute vec4 a_Position;\n' +
    'uniform mat4 u_ModelMatrix;\n' +
    'void main() {\n' +
    '  gl_Position = u_ModelMatrix * u_ModelMatrix * a_Position;\n' +
    '}\n';
  
  // Fragment shader program
  var FSHADER_SOURCE =
    'void main() {\n' +
    '  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n' +
    '}\n';
  
  function main() {
    // Retrieve <canvas> element
    var canvas = document.getElementById('webgl');
  
    // Get the rendering context for WebGL
    var gl = getWebGLContext(canvas);
    if (!gl) {
      console.log('Failed to get the rendering context for WebGL');
      return;
    }
  
    // Initialize shaders
    if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
      console.log('Failed to intialize shaders.');
      return;
    }
  
    // Write the positions of vertices to a vertex shader
    var n = initVertexBuffers(gl);
    if (n < 0) {
      console.log('Failed to set the positions of the vertices');
      return;
    }
  
    // Create Matrix4 object for model transformation
    var modelMatrix = new Matrix4();
  
    // Calculate a model matrix
    var ANGLE = 60.0; // The rotation angle
    var Tx = 0.5;     // Translation distance
    modelMatrix.setRotate(ANGLE, 0, 0, 1);  // Set rotation matrix
    modelMatrix.translate(Tx, 0, 0);        // Multiply modelMatrix by the calculated translation matrix
  
    // Pass the model matrix to the vertex shader
    var u_ModelMatrix = gl.getUniformLocation(gl.program, 'u_ModelMatrix');
    if (!u_ModelMatrix) {
      console.log('Failed to get the storage location of u_xformMatrix');
      return;
    }
    gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements);
  
    // Specify the color for clearing <canvas>
    gl.clearColor(0, 0, 0, 1);
  
    // Clear <canvas>
    gl.clear(gl.COLOR_BUFFER_BIT);
  
    // Draw the rectangle
    gl.drawArrays(gl.TRIANGLES, 0, n);
  }
  
  function initVertexBuffers(gl) {
    var vertices = new Float32Array([
      0, 0.3,   -0.3, -0.3,   0.3, -0.3
    ]);
    var n = 3; // The number of vertices
  
    // Create a buffer object
    var vertexBuffer = gl.createBuffer();
    if (!vertexBuffer) {
      console.log('Failed to create the buffer object');
      return false;
    }
  
    // Bind the buffer object to target
    gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
    // Write date into the buffer object
    gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
  
    var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
    if (a_Position < 0) {
      console.log('Failed to get the storage location of a_Position');
      return -1;
    }
    // Assign the buffer object to a_Position variable
    gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
  
    // Enable the assignment to a_Position variable
    gl.enableVertexAttribArray(a_Position);
  
    return n;
  }
  
  