code: function drawPass (bindings, passIndex, passCount, outputFBO) {
    var { debugFBO, gl, canvas, shader, quad, resolution, scale, offset } = bindings
    var { uniforms } = shader
    var { width, height } = canvas
  
    debugFBO.bind()
    shader.bind()
  
    // update shader
    var resizeResolutionX = width / passCount * (1 - MARGIN * 2)
    var resizeResolutionY = height / passCount * (1 - MARGIN * 2)
    resolution[0] = width
    resolution[1] = height
    scale[0] = width / resizeResolutionX
    scale[1] = height / resizeResolutionY
    var scissorOffsetX = width * passIndex / passCount + width / passCount * MARGIN
    var scissorOffsetY = (height / 2) - (resizeResolutionY / 2)
    offset[0] = scissorOffsetX / width
    offset[1] = scissorOffsetY / height
    uniforms.uOffset = offset
    uniforms.uResolution = resolution
    uniforms.uScale = scale
    uniforms.uInput = outputFBO.color[0].bind(0)
  
    // set scissor
    gl.enable(gl.SCISSOR_TEST)
    gl.scissor(
      // coordinate of lower left of box, moving up and to the right
      scissorOffsetX,
      scissorOffsetY,
      resizeResolutionX,
      resizeResolutionY
    )
  
    // clear first, then draw on it
    gl.clearColor(0,0,0,1)
    gl.clear(gl.COLOR_BUFFER_BIT)
    gl.disable(gl.DEPTH_TEST)
    RenderScreen(gl)
  
    // reset state
    gl.bindFramebuffer(gl.FRAMEBUFFER, null)
    gl.disable(gl.SCISSOR_TEST)
    gl.enable(gl.DEPTH_TEST)
    gl.scissor(0, 0, width, height)
  }
docs: Draw a small thumbnail image of the output