 [0, -10, 0, 10, 10, 0, -10, 10, 0], },
     texcoord: { numComponents: 2, data: [0.5, 0, 1, 1, 0, 1],               },
     normal:   { numComponents: 3, data: [0, 0, 1, 0, 0, 1, 0, 0, 1],        },
  };
  var bufferInfo = twgl.createBufferInfoFromArrays(gl, arrays);

  // setup GLSL program
  var program = twgl.createProgramFromSources(gl, [vs, fs]);
  var uniformSetters = twgl.createUniformSetters(gl, program);
  var attribSetters  = twgl.createAttributeSetters(gl, program);

  var vao = twgl.createVAOFr