// Uses half-sample symmetry.
func Symmetric(im image.Image, p image.Point) color.Color {
b := im.Bounds()
// Make twice as big.
d := image.Rectangle{b.Min, b.Max.Add(b.Size())}
p = p.Mod(d)
// Move to origin.
p = p.Sub(b.Min)
w, h := b.Dx(), b.Dy()
if p.X > w-1 {
p.X = 2*w - 1 - p.X
}
if p.Y > h-1 {
p.Y = 2*h - 1 - p.Y
}
p = p.Add(b.Min)
return im.At(p.X, p.Y)
}
func Periodic(im image.Image, p image.Point) color.Color {
p = p.Mod(im.Bounds())
return im.At(p.X, p.Y)
}