height);
  }

  let fbiA = makeFramebufferAndTexture(gl, 512, 512);
  let fbiB = makeFramebufferAndTexture(gl, 512, 512);
  
  function drawImageAndPreviousFrameToTextureB() {
    bindFramebufferAndSetViewport(gl, fbiB);
    
    // calls gl.bindBuffer, gl.enableVertexAttribArray, gl.vertexAttribPointer
    // for each attribute
    twgl.setBuffersAndAttributes(gl, programInfo, quadBufferInfo);

    // calls gl.activeTexture, gl.bindTexture, gl.uniform 
    twgl.setUniforms(programInfo, {
      u_tex: image