internal/restorable/image.go
func (i *Image) dependingImages() map[*Image]struct{} {
	r := map[*Image]struct{}{}
	for _, c := range i.drawTrianglesHistory {
		r[c.image] = struct{}{}
	}
	return r
}
func (i *Image) dependingImages() map[*Image]struct{} {
	r := map[*Image]struct{}{}
	for _, c := range i.drawTrianglesHistory {
		r[c.image] = struct{}{}
	}
	return r
}
// dependingImages returns all images that is depended by the image.