Example
Most of image type in image package having SubImage(r Rectangle) Image method, except image.Uniform. Based on this fact, We can implement a function to crop an arbitrary image as follows
func CropImage(img image.Image, cropRect image.Rectangle) (cropImg image.Image, newImg bool) {
//Interface for asserting whether `img`
//implements SubImage or not.
//This can be defined globally.
type CropableImage interface {
image.Image
SubImage(r image.Rectangle) image.Image
}
if p, ok := img.(CropableImage); ok {
// Call SubImage. This should be fast,
// since SubImage (usually) shares underlying pixel.
cropImg = p.SubImage(cropRect)
} else if cropRect = cropRect.Intersect(img.Bounds()); !cropRect.Empty() {
// If `img` does not implement `SubImage`,
// copy (and silently convert) the image portion to RGBA image.
rgbaImg := image.NewRGBA(cropRect)
for y := cropRect.Min.Y; y < cropRect.Max.Y; y++ {
for x := cropRect.Min.X; x < cropRect.Max.X; x++ {
rgbaImg.Set(x, y, img.At(x, y))
}
}
cropImg = rgbaImg
newImg = true
} else {
// Return an empty RGBA image
cropImg = &image.RGBA{}
newImg = true
}
return cropImg, newImg
}
Note that the cropped image may shared its underlying pixels with the original image. If this is the case, any modification to the cropped image will affect the original image.
