code: func (i *Image) Fill(clr color.Color) error {
  	i.copyCheck()
  	if i.isDisposed() {
  		return nil
  	}
  
  	// TODO: Implement this.
  	if i.isSubImage() {
  		panic("ebiten: render to a subimage is not implemented (Fill)")
  	}
  
  	i.resolvePendingPixels(false)
  
  	r16, g16, b16, a16 := clr.RGBA()
  	r, g, b, a := uint8(r16>>8), uint8(g16>>8), uint8(b16>>8), uint8(a16>>8)
  	i.mipmap.original().Fill(r, g, b, a)
  	i.disposeMipmaps()
  	return nil
  }
docs: // Fill fills the image with a solid color.
  //
  // When the image is disposed, Fill does nothing.
  //
  // Fill always returns nil as of 1.5.0-alpha.