code: func (i *Image) internalSize() (int, int) {
  	if i.w2 == 0 || i.h2 == 0 {
  		w, h := i.image.Size()
  		i.w2 = graphics.InternalImageSize(w)
  		i.h2 = graphics.InternalImageSize(h)
  	}
  	return i.w2, i.h2
  }
docs: // internalSize returns the size of the internal texture.