 gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
      -0.1,  0.4,
      -0.1, -0.4,
       0.1, -0.4,
      -0.1,  0.4,
       0.1, -0.4,
       0.1,  0.4,
      -0.4, -0.1,
       0.4, -0.1,
      -0.4,  0.1,
      -0.4,  0.1,
       0.4, -0.1,
       0.4,  0.1,
    ]), gl.STATIC_DRAW);
  const numVertices = 12;

  // setup the position attribute
  gl.enableVertexAttribArray(positionLoc);
  gl.vertexAttribPointer(
      positionLoc, 