better_rotate.go

func RotatedImage(i *ebiten.Image, rotation float64) *ebiten.Image {
	if i == nil {
		return i
	}

	w, h := i.Size()
	maxDim := int(math.Hypot(float64(w), float64(h)))
	newimage := ebiten.NewImage(maxDim, maxDim)

	op := ebiten.DrawImageOptions{}
	op.GeoM.Translate(-float64(w/2), -float64(h/2))
	op.GeoM.Rotate(rotation)
	op.GeoM.Translate(float64(maxDim/2), float64(maxDim/2))
	newimage.DrawImage(i, &op)

	return newimage
}