code: func (i *Image) Fill(r, g, b, a uint8) {
  	backendsM.Lock()
  	if i.disposed {
  		panic("shareable: the drawing target image must not be disposed (Fill)")
  	}
  	i.ensureNotShared()
  
  	i.backend.restorable.Fill(r, g, b, a)
  
  	backendsM.Unlock()
  }
docs: // Fill fills the image with a color. This affects not only the (0, 0)-(width, height) region but also the whole
  // framebuffer region.