func (g GID) SetValue() uint32 {
	return g.gid
}
SetValue sets the true GID value packed with rotation data
package common
import "fmt"
const (
	tileFlippedHorizontal = 0x80000000
	tileFlippedVertical   = 0x40000000
	tileFlippedDiagonal   = 0x20000000
	tileFlipped           = tileFlippedHorizontal | tileFlippedVertical | tileFlippedDiagonal
)
type GID struct {
	gid uint32
}
func NewGID(gid uint32) (g GID) {
	g = GID{
		gid: gid,
	}
	return
}
func (g GID) Index() uint32 {
	return uint32(g.gid &^ tileFlipped)
}
func (g GID) Value() uint32 {
	return g.gid
}