finstr/crop/crop.go

package crop

import (
	"errors"
	"image"

	goutil "git.fireandbrimst.one/aw/goutil/misc"
)

func boundInt(i, min, max int) int {
	return goutil.IntMin(goutil.IntMax(i, min), max)
}

func bound(p image.Point, bounds image.Rectangle) image.Point {
	min := bounds.Min
	max := bounds.Max
	return image.Point{X: boundInt(p.X, min.X, max.X), Y: boundInt(p.Y, min.Y, max.Y)}
}

type subImageSupport interface {
	SubImage(rec image.Rectangle) image.Image
}

func Crop(img image.Image, topleft image.Point, w int, h int) (image.Image, error) {
	bounds := img.Bounds()
	topleft = bound(topleft, bounds)
	bottomright := bound(image.Point{X: topleft.X + w, Y: topleft.Y + h}, bounds)
	croparea := image.Rect(topleft.X, topleft.Y, bottomright.X, bottomright.Y)
	if timg, ok := img.(subImageSupport); ok {
		return timg.SubImage(croparea), nil
	} else {
		return nil, errors.New("Crop: image format does not support 'SubImage' method (cropping not supported)")
	}
}

func CropCenter(img image.Image, w int, h int) (image.Image, error) {
	bounds := img.Bounds()
	center := image.Point{X: bounds.Min.X + bounds.Dx()/2, Y: bounds.Min.Y + bounds.Dy()/2}
	topleft := image.Point{X: center.X - w/2, Y: center.Y - h/2}
	return Crop(img, topleft, w, h)
}