生命不止，继续 go go go~~~~

今天做一点图片处理的东西，跟大家一起学习分享。

很久之前，介绍过golang提供的关于图片的标准库：
Go语言学习之image、image/color、image/png、image/jpeg包(the way to go)

当你search on google或百度一下的时候，你会发现很多提到了graphics-go/graphics，但是这个库不知道为何，官方好像不再提供了，很难找到了。

那也没关系，我们还有面向github编程呢！！！

温故而知新，先看一下之前的代码：
生成图片

package main

import "image"
import "image/color"
import "image/png"
import "os"

func main() {
    // Create an 100 x 50 image
    img := image.NewRGBA(image.Rect(0, 0, 100, 50))

    // Draw a red dot at (2,3)
    img.Set(2, 3,color.RGBA{255, 255})

    // Save to out.png
    f,_ := os.OpenFile("out.png",os.O_WRONLY|os.O_CREATE, 0600)
    defer f.Close()
    png.Encode(f,img)
}

disintegration/imaging

github地址：
https://github.com/disintegration/imaging

Star: 1284

获取：
go get -u github.com/disintegration/imaging

生成缩略图
下面的代码，将三张图片生成一张缩略图。
出自：
https://www.socketloop.com/tutorials/golang-generate-thumbnails-from-images

package main

import (
    "image"
    "image/color"
    "runtime"

    "github.com/disintegration/imaging"
)

func main() {
    // use all cpu cores for maximum performance
    runtime.GOMAXPROCS(runtime.Numcpu())

    // input files
    files := []string{"1.jpg","2.jpg","3.jpg"}

    // load images and make 100x100 thumbnails of them
    var thumbnails []image.Image
    for _,file := range files {
        img,err := imaging.Open(file)
        if err != nil {
            panic(err)
        }
        thumb := imaging.Thumbnail(img,imaging.CatmullRom)
        thumbnails = append(thumbnails,thumb)
    }

    // create a new blank image
    dst := imaging.New(100*len(thumbnails),color.NRGBA{0, 0})

    // paste thumbnails into the new image side by side
    for i,thumb := range thumbnails {
        dst = imaging.Paste(dst,thumb,image.Pt(i*100, 0))
    }

    // save the combined image to file
    err := imaging.Save(dst,"dst.jpg")
    if err != nil {
        panic(err)
    }
}

生成缩略图服务
接下来，根据用户提供的url，生成不同尺寸的缩略图。

关于golang中net/http可以参考：
Go语言学习之net/http包(The way to go)

package main

import (
    "fmt"
    "image"
    "image/color"
    "image/png"
    "net/http"
    "runtime"
    "strconv"
    "strings"

    "github.com/disintegration/imaging"
)

func main() {
    // use all cpu cores for maximum performance
    runtime.GOMAXPROCS(runtime.Numcpu())
    http.HandleFunc("/",doImageHandler)
    http.ListenAndServe("localhost:8080",nil)
}
func doImageHandler(w http.ResponseWriter,r *http.Request) {
    fmt.Printf("%q\n",strings.Split(r.URL.Path,"/"))
    url := strings.Split(r.URL.Path,"/")
    if len(url) != 3 {
        return
    }

    thumbnails_size := strings.Split(url[2],"_")
    if len(thumbnails_size) != 2 {
        return
    }
    thumbnails_width,_ := strconv.Atoi(thumbnails_size[0])
    thumbnails_height,_ := strconv.Atoi(thumbnails_size[1])

    img,err := imaging.Open(url[1])
    if err != nil {
        panic(err)
    }
    thumb := imaging.Thumbnail(img,thumbnails_width,thumbnails_height,imaging.CatmullRom)
    dst := imaging.New(thumbnails_width, 0})
    dst = imaging.Paste(dst,image.Pt(0, 0))

    if err != nil {
        panic(err)
    }
    header := w.Header()
    header.Add("Content-Type","image/jpeg")

    png.Encode(w,dst)
}

例如，浏览器输入：http://localhost:8080/1.jpg/80_90
就会生成一张80*90的1.jpg的缩略图

nfnt/resize

github地址:
https://github.com/nfnt/resize

Star: 1544

获取：
go get github.com/nfnt/resize

等比例放大缩小图片

package main

import (
    "image/jpeg"
    "log"
    "os"

    "github.com/nfnt/resize"
)

func main() {
    file,err := os.Open("1.jpg")
    if err != nil {
        log.Fatal(err)
    }

    img,err := jpeg.Decode(file)
    if err != nil {
        log.Fatal(err)
    }
    file.Close()

    // resize to width 1000 using Lanczos resampling
    // and preserve aspect ratio
    m := resize.Resize(100,img,resize.Lanczos3)

    out,err := os.Create("test_resized.jpg")
    if err != nil {
        log.Fatal(err)
    }
    defer out.Close()

    // write new image to file
    jpeg.Encode(out,m,nil)
}