internal/graphics/math.go
func InternalImageSize(x int) int {
	if x <= 0 {
		panic("graphics: x must be positive")
	}
	if x < minInternalImageSize {
		return minInternalImageSize
	}
	r := 1
	for r < x {
		r <<= 1
	}
	return r
}
func InternalImageSize(x int) int {
	if x <= 0 {
		panic("graphics: x must be positive")
	}
	if x < minInternalImageSize {
		return minInternalImageSize
	}
	r := 1
	for r < x {
		r <<= 1
	}
	return r
}
// InternalImageSize returns a nearest appropriate size as an internal image.