golang圖片的切割與縮小

package main

import (
	"errors"
	"fmt"
	"image"
	"image/gif"
	"image/jpeg"
	"image/png"
	"io"
	"os"
	"strings"

	"golang.org/x/image/bmp"

	"github.com/nfnt/resize"
)

func main() {
	src := "data/1.gif"
	dst := strings.Replace(src, ".", "_small.", 1)
	fmt.Println("src=", src, " dst=", dst)
	fIn, _ := os.Open(src)
	defer fIn.Close()

	fOut, _ := os.Create(dst)
	defer fOut.Close()

	// err := clip(fIn, fOut, 0, 0, 150, 150, 100)
	// if err != nil {
	// panic(err)
	// }
	err := scale(fIn, fOut, 150, 150, 100)
	if err != nil {
		panic(err)
	}
}

/*
* 圖片裁剪
* 入參:
* 規則:如果精度爲0則精度保持不變
*
* 返回:error
 */
func clip(in io.Reader, out io.Writer, x0, y0, x1, y1, quality int) error {
	origin, fm, err := image.Decode(in)
	if err != nil {
		return err
	}

	switch fm {
	case "jpeg":
		img := origin.(*image.YCbCr)
		subImg := img.SubImage(image.Rect(x0, y0, x1, y1)).(*image.YCbCr)
		return jpeg.Encode(out, subImg, &jpeg.Options{quality})
	case "png":
		switch canvas.(type) {
		case *image.NRGBA:
			img := canvas.(*image.NRGBA)
			subImg := img.SubImage(image.Rect(x0, y0, x1, y1)).(*image.NRGBA)
			return png.Encode(out, subImg)
		case *image.RGBA:
			img := canvas.(*image.RGBA)
			subImg := img.SubImage(image.Rect(x0, y0, x1, y1)).(*image.RGBA)
			return png.Encode(out, subImg)
		}
	case "gif":
		img := origin.(*image.Paletted)
		subImg := img.SubImage(image.Rect(x0, y0, x1, y1)).(*image.Paletted)
		return gif.Encode(out, subImg, &gif.Options{})
	case "bmp":
		img := origin.(*image.RGBA)
		subImg := img.SubImage(image.Rect(x0, y0, x1, y1)).(*image.RGBA)
		return bmp.Encode(out, subImg)
	default:
		return errors.New("ERROR FORMAT")
	}
	return nil
}

/*
* 縮略圖生成
* 入參:
* 規則: 如果width 或 hight其中有一個爲0，則大小不變 如果精度爲0則精度保持不變
* 矩形座標系起點是左上
* 返回:error
 */
func scale(in io.Reader, out io.Writer, width, height, quality int) error {
	origin, fm, err := image.Decode(in)
	if err != nil {
		return err
	}
	if width == 0 || height == 0 {
		width = origin.Bounds().Max.X
		height = origin.Bounds().Max.Y
	}
	if quality == 0 {
		quality = 100
	}
	canvas := resize.Thumbnail(uint(width), uint(height), origin, resize.Lanczos3)

	//return jpeg.Encode(out, canvas, &jpeg.Options{quality})

	switch fm {
	case "jpeg":
		return jpeg.Encode(out, canvas, &jpeg.Options{quality})
	case "png":
		return png.Encode(out, canvas)
	case "gif":
		return gif.Encode(out, canvas, &gif.Options{})
	case "bmp":
		return bmp.Encode(out, canvas)
	default:
		return errors.New("ERROR FORMAT")
	}
	return nil
}