app icon creation

main.go

package main

import (
	"bytes"
	"fmt"
	ico "github.com/Kodeworks/golang-image-ico"
	"github.com/nfnt/resize"
	"image"
	"image/gif"
	"image/png"
	"io"
	"io/ioutil"
	"os"
	"path"
	"strings"
)

const outputPath = "out"

type target struct {
	n string
	w uint
	h uint
	f bool
	e encodeFunc
}

type encodeFunc func(io.Writer, image.Image) error

var targets = []target{
	{n: "apple-touch-icon-%vx%v.png", w: 114, h: 114, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 120, h: 120, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 128, h: 128, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 144, h: 144, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 152, h: 152, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 180, h: 180, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 57, h: 57, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 60, h: 60, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 72, h: 72, e: png.Encode},
	{n: "apple-touch-icon-%vx%v.png", w: 76, h: 76, e: png.Encode},
	{n: "apple-touch-icon.png", w: 0, h: 0, e: png.Encode},
	{n: "apple-touch-icon-precomposed.png", w: 0, h: 0, e: png.Encode},
	{n: "favicon-%vx%v.png", w: 160, h: 160, e: png.Encode},
	{n: "favicon-%vx%v.png", w: 16, h: 16, e: png.Encode},
	{n: "favicon-%vx%v.png", w: 192, h: 192, e: png.Encode},
	{n: "favicon-%vx%v.png", w: 196, h: 196, e: png.Encode},
	{n: "favicon-%vx%v.png", w: 32, h: 32, e: png.Encode},
	{n: "favicon-%vx%v.png", w: 96, h: 96, e: png.Encode},
	{n: "win8-tile-%vx%v.png", w: 144, h: 144, e: png.Encode},
	{n: "win8-tile-%vx%v.png", w: 150, h: 150, e: png.Encode},
	{n: "win8-tile-%vx%v.png", w: 310, h: 310, e: png.Encode},
	{n: "win8-tile-%vx%v.png", w: 310, h: 150, e: png.Encode},
	{n: "win8-tile-%vx%v.png", w: 70, h: 70, e: png.Encode},
	{n: "favicon.gif", w: 0, h: 0, e: encodeGif},
	{n: "favicon.ico", w: 16, h: 16, e: ico.Encode},
	{n: "favicon.png", w: 0, h: 0, e: png.Encode},
}

func main() {
	must(os.RemoveAll(outputPath))
	must(os.MkdirAll(outputPath, 0777))

	img := getSourceImage()

	for _, target := range targets {
		newImage := resize.Resize(target.w, target.h, img, resize.Lanczos3)

		f, err := os.Create(path.Join(outputPath, getFilename(target)))
		panicOnError(err)

		must(target.e(f, newImage))

		must(f.Close())
	}
}

func getSourceImage() image.Image {
	b, err := ioutil.ReadFile("icon.png")
	panicOnError(err)

	img, err := png.Decode(bytes.NewReader(b))
	panicOnError(err)

	return img
}

func encodeGif(w io.Writer, i image.Image) error {
	return gif.Encode(w, i, &gif.Options{})
}

func getFilename(target target) string {
	var filename = target.n
	if strings.Contains(target.n, "%v") {
		filename = fmt.Sprintf(target.n, target.w, target.h)
	}
	return filename
}

func must(err error) {
	panicOnError(err)
}

func panicOnError(err error) {
	if err != nil {
		panic(err)
	}
}