golang image append , support jpg / png / webp

image_merge_main.go

package main

import (
	"bytes"
	"fmt"
	"image"
	"image/draw"
	"image/jpeg"
	"image/png"
	"io/ioutil"
	"os"

	"golang.org/x/image/webp"
)

// only support jpg , png , webp
// webp only support read

type ImageType int

const (
	ImageTypeJPG ImageType = iota + 1
	ImageTypePNG
	ImageTypeWEBP
)

// ImageTypeFileHead fast filetype check
var ImageTypeFileHead = map[ImageType][]byte{
	ImageTypeJPG:  {0xFF, 0xD8, 0xFF},
	ImageTypePNG:  {0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A},
	ImageTypeWEBP: {0x52, 0x49, 0x46, 0x46},
}

func getImage(filePath string) (img *image.Image, err error) {
	var data []byte
	data, err = ioutil.ReadFile(filePath)
	if err != nil {
		return
	}

	var imageType *ImageType
	for tempImageType, tempImageFileHead := range ImageTypeFileHead {
		if len(data) < len(tempImageFileHead) {
			continue
		}
		if bytes.Equal(data[:len(tempImageFileHead)], tempImageFileHead) {
			imageType = &tempImageType
			break
		}
	}
	if imageType == nil {
		err = fmt.Errorf("image file not support , file head not match")
		return
	}
	var tempImg image.Image
	switch *imageType {
	case ImageTypeJPG:
		tempImg, err = jpeg.Decode(bytes.NewReader(data))
	case ImageTypePNG:
		tempImg, err = png.Decode(bytes.NewReader(data))
	case ImageTypeWEBP:
		tempImg, err = webp.Decode(bytes.NewReader(data))
	default:
		err = fmt.Errorf("image file not support , file head not match")
	}
	if err == nil {
		img = &tempImg
	}
	return
}

func saveImage(img image.Image, filePath string, imageType ImageType, jpgQuality *int) (err error) {
	f, err := os.Create(filePath)
	if err != nil {
		return
	}
	defer f.Close()

	switch imageType {
	case ImageTypeJPG:
		if jpgQuality == nil {
			temp := 80 // default 80
			jpgQuality = &temp
		}
		err = jpeg.Encode(f, img, &jpeg.Options{Quality: *jpgQuality})
	case ImageTypePNG:
		err = png.Encode(f, img)
	default:
		err = fmt.Errorf("unknow image type to save file")
	}
	return
}

func mergeImage(fileList []string) (rgbaConvas *image.RGBA64, err error) {
	var imageSize image.Point
	for index, fileName := range fileList {
		var imgP *image.Image
		imgP, err = getImage(fileName)
		if err != nil {
			return
		}
		img := *imgP
		if index == 0 {
			imageSize = img.Bounds().Max
			rgbaConvas = image.NewRGBA64(image.Rectangle{image.Point{0, 0}, img.Bounds().Max}) // create empty canvas
		}
		if !img.Bounds().Max.Eq(imageSize) {
			tImageSize := img.Bounds().Max
			err = fmt.Errorf("image not all match , image(%d:%d) , [%d:%s](%d:%d)", imageSize.X, imageSize.Y, index, fileName, tImageSize.X, tImageSize.Y)
			return
		}
		draw.Draw(rgbaConvas, img.Bounds(), img, image.Point{0, 0}, draw.Over) // draw image to canvas
	}
	if rgbaConvas == nil {
		err = fmt.Errorf("empty canvas")
		return
	}
	return
}

func main() {
	img, err := mergeImage([]string{
		"layer1.webp", "layer2.png", "layer3.webp", "layer4.png",
	})
	if err != nil {
		fmt.Println("ERR", err)
		return
	}
	err = saveImage(img, "final.png", ImageTypePNG, nil)
	if err != nil {
		fmt.Println("ERR", err)
		return
	}
	fmt.Println("finished!")
}