golang使用image包及draw.Draw合成图片

 在golang中合成图片，一般使用image包及draw.Draw即可，images包的具体方法和用法：https://studygolang.com/pkgdoc

代码中图片缩放的包：github.com/nfnt/resize

/**
从url中获取图片资源
 */
func readImgData(url string) image.Image {
   resp, err := http.Get(url)
   if err != nil {
      logs.Info("图片获取失败", err)
      return nil
   }
   defer resp.Body.Close()
   img,_,err := image.Decode(resp.Body)
   if err != nil {
      logs.Info("图片decode失败", err)
      return nil
   }
   return img
}


// 计算图片缩放后的尺寸
func calculateRatioFit(srcWidth, srcHeight int, defaultWidth, defaultHeight float64) (int, int) {
	ratio := math.Min(defaultWidth/float64(srcWidth), defaultHeight/float64(srcHeight))
	return int(math.Ceil(float64(srcWidth) * ratio)), int(math.Ceil(float64(srcHeight) * ratio))
}

/**
3图合1，创建图片
*/
func CreatePicture(img1Url, img2Url, img3Url string) (map[string]interface{},bool) {
	returnData := make(map[string]interface{})
	if img1Url == "" || img2Url == "" || img3Url == "" {
		return nil, false
	}
	//根据图片地址获取图片.
	img1 := readImgData(img1Url)
	img2 := readImgData(img2Url)
	img3 := readImgData(img3Url)
	if img1 == nil || img2 == nil || img3 == nil {
		return nil, false
	}
	//图片1缩放
	b1 := img1.Bounds()
	img1Width := b1.Max.X
	img1Height := b1.Max.Y
	w1, h1 := calculateRatioFit(img1Width, img1Height, 344, 344)
	img1m := resize.Resize(uint(w1), uint(h1), img1, resize.Lanczos3)
	//图片2缩放
	b2 := img2.Bounds()
	img2Width := b2.Max.X
	img2Height := b2.Max.Y
	w2, h2 := calculateRatioFit(img2Width, img2Height, 172, 172)
	img2m := resize.Resize(uint(w2), uint(h2), img2, resize.Lanczos3)
	//图片3缩放
	b3 := img3.Bounds()
	img3Width := b3.Max.X
	img3Height := b3.Max.Y
	w3, h3 := calculateRatioFit(img3Width, img3Height, 172, 172)
	img3m := resize.Resize(uint(w3), uint(h3), img3, resize.Lanczos3)
	//创建源图
	fileName := "dst.jpg"
	file, err := os.Create(fileName)
	if err != nil {
		return nil,false
	}
	defer func() {
		err := file.Close()
		if err != nil {
			logs.Info("CreateGoodsPicture:图片资源关闭错误", err)
		}
	}()
	//图片三合一绘图
	jpg := image.NewRGBA(image.Rect(0, 0, 344, 516))
	draw.Draw(jpg, jpg.Bounds().Add(image.Pt(0,0)), img1m, img1m.Bounds().Min, draw.Src)
	draw.Draw(jpg, jpg.Bounds().Add(image.Pt(0,344)), img2m, img2m.Bounds().Min, draw.Src)
	draw.Draw(jpg, jpg.Bounds().Add(image.Pt(172,344)), img3m, img3m.Bounds().Min, draw.Src)
	//jpeg.Encode默认图片质量75%
	err1 := jpeg.Encode(file, jpg, nil)
	if err1 != nil {
		logs.Info("CreateGoodsPicture:图片png.Encode错误", err1)
		return nil, false
	}
	
	defer func() {
		err := os.Remove(fileName)
		if err != nil {
			logs.Info("CreateGoodsPicture:图片资源删除错误", err)
		}
	}()
	return returnData, true
}