text: var triangleVertexPositionBuffer;
  var squareVertexPositionBuffer;
  
  function webGLStart() {
      var canvas = document.getElementById("lesson01-canvas");
      initGL(canvas);
      initShaders();
      initBuffers();
  
      gl.clearColor(0.0, 0.0, 0.0, 1.0);
      gl.enable(gl.DEPTH_TEST);
  
      drawScene();
  }
  
  function initBuffers() {
      triangleVertexPositionBuffer = gl.createBuffer();
      gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexPositionBuffer);
      var vertices = [
          0.0,  1.0,  0.0,
          -1.0, -1.0,  0.0,
          1.0, -1.0,  0.0
      ];
      gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
      triangleVertexPositionBuffer.itemSize = 3;
      triangleVertexPositionBuffer.numItems = 3;
      
      squareVertexPositionBuffer = gl.createBuffer();
      gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
      vertices = [
          1.0,  1.0,  0.0,
          -1.0,  1.0,  0.0,
          1.0, -1.0,  0.0,
          -1.0, -1.0,  0.0
      ];
      gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
      squareVertexPositionBuffer.itemSize = 3;
      squareVertexPositionBuffer.numItems = 4;
  }
  
  function drawScene() {
      gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
  
  }