Add Crop package for cropping image.Images.

internal/crop/LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2014 Olivier Amblet
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

internal/crop/README.md

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+## Crop
+
+This is a modified version of https://github.com/oliamb/cutter.
+License is detailed in LICENSE.

internal/crop/crop.go

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+package crop
+
+import (
+	"image"
+	"image/draw"
+)
+
+// An interface that is
+// image.Image + SubImage method.
+type subImageSupported interface {
+	SubImage(r image.Rectangle) image.Image
+}
+
+// Cropper is the interface used to crop images
+type Cropper interface {
+	Crop(img image.Image, width, height int, anchor image.Point) (image.Image, error)
+}
+
+// CropperFunc exposes a Crop function that calls itself.
+// It implements Cropper.
+type CropperFunc func(img image.Image, width, height int, anchor image.Point) (image.Image, error)
+
+// Crop calls the CropperFunc
+func (c CropperFunc) Crop(img image.Image, width, height int, anchor image.Point) (image.Image, error) {
+	return c(img, width, height, anchor)
+}
+
+// Crop retrieves an image that is a
+// cropped copy of the original img.
+func Crop(img image.Image, width, height int, anchor image.Point) (image.Image, error) {
+	maxBounds := maxBounds(anchor, img.Bounds())
+	size := computeSize(maxBounds, image.Point{width, height})
+	cr := computedCropArea(anchor, img.Bounds(), size)
+	cr = img.Bounds().Intersect(cr)
+
+	if dImg, ok := img.(subImageSupported); ok {
+		return dImg.SubImage(cr), nil
+	}
+	return cropWithCopy(img, cr)
+}
+
+func cropWithCopy(img image.Image, cr image.Rectangle) (image.Image, error) {
+	result := image.NewRGBA(cr)
+	draw.Draw(result, cr, img, cr.Min, draw.Src)
+	return result, nil
+}
+
+func maxBounds(anchor image.Point, bounds image.Rectangle) image.Rectangle {
+	return image.Rect(anchor.X, anchor.Y, bounds.Max.X, bounds.Max.Y)
+}
+
+// computeSize retrieve the effective size of the cropped image.
+func computeSize(bounds image.Rectangle, ratio image.Point) image.Point {
+	return image.Point{ratio.X, ratio.Y}
+}
+
+// computedCropArea retrieve the theorical crop area.
+func computedCropArea(anchor image.Point, bounds image.Rectangle, size image.Point) (r image.Rectangle) {
+	min := bounds.Min
+	rMin := image.Point{min.X + anchor.X, min.Y + anchor.Y}
+	return image.Rect(rMin.X, rMin.Y, rMin.X+size.X, rMin.Y+size.Y)
+}

internal/crop/crop_suite_test.go

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+package crop_test
+
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+
+	"testing"
+)
+
+func TestCrop(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Crop Suite")
+}

internal/crop/crop_test.go

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+package crop
+
+import (
+	"image"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Crop", func() {
+	It("crops the image", func() {
+		r, err := Crop(getImage(), 512, 400, image.Point{})
+		Expect(err).NotTo(HaveOccurred())
+		Expect(r.Bounds().Dx()).To(Equal(512))
+		Expect(r.Bounds().Dy()).To(Equal(400))
+		Expect(r.Bounds().Min.X).To(Equal(0))
+		Expect(r.Bounds().Min.Y).To(Equal(0))
+	})
+
+	Context("when a different anchor point is used", func() {
+		It("crops the image", func() {
+			r, err := Crop(getImage(), 512, 400, image.Point{X: 100, Y: 50})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(r.Bounds().Dx()).To(Equal(512))
+			Expect(r.Bounds().Dy()).To(Equal(400))
+			Expect(r.Bounds().Min.X).To(Equal(100))
+			Expect(r.Bounds().Min.Y).To(Equal(50))
+		})
+	})
+})
+
+func getImage() image.Image {
+	return image.NewGray(image.Rect(0, 0, 1600, 1437))
+}