geom.go
func (g *GeoM) SetElement(i, j int, element float64) {
	e := float32(element)
	switch {
	case i == 0 && j == 0:
		g.a_1 = e - 1
	case i == 0 && j == 1:
		g.b = e
	case i == 0 && j == 2:
		g.tx = e
	case i == 1 && j == 0:
		g.c = e
	case i == 1 && j == 1:
		g.d_1 = e - 1
	case i == 1 && j == 2:
		g.ty = e
	default:
		panic("ebiten: i or j is out of index")
	}
}
func (g *GeoM) SetElement(i, j int, element float64) {
	e := float32(element)
	switch {
	case i == 0 && j == 0:
		g.a_1 = e - 1
	case i == 0 && j == 1:
		g.b = e
	case i == 0 && j == 2:
		g.tx = e
	case i == 1 && j == 0:
		g.c = e
	case i == 1 && j == 1:
		g.d_1 = e - 1
	case i == 1 && j == 2:
		g.ty = e
	default:
		panic("ebiten: i or j is out of index")
	}
}
// SetElement sets an element at (i, j).