code: def shade(renderbuffer, bufferbbox, img3d, bbox):
    
  
    if not Bbox.intersects(bufferbbox, bbox):
      return
  
    spt = max2(bbox.minpt, bufferbbox.minpt)
    ept = min2(bbox.maxpt, bufferbbox.maxpt)
  
    ZERO3 = Vec(0,0,0)
  
    istart = max2(spt - bbox.minpt, ZERO3)
    iend = min2(ept - bbox.maxpt, ZERO3) + img3d.shape[:3]
  
    rbox = Bbox(spt, ept) - bufferbbox.minpt
    if len(img3d.shape) == 3:
      img3d = img3d[ :, :, :, np.newaxis]
    
    renderbuffer[ rbox.to_slices() ] = img3d[ istart.x:iend.x, istart.y:iend.y, istart.z:iend.z, : ]
docs: Shade a renderbuffer with a downloaded chunk. 
      The buffer will only be painted in the overlapping
      region of the content.