Resize Icon for unity

main.go

package main

import (
	"bytes"
	"fmt"
	"github.com/nfnt/resize"
	"image"
	"image/png"
	"io"
	"io/ioutil"
	"os"
	"path"
	"strings"
)

const outputPath = "out"
const baseName = "icon"
const baseImage = "icon-512.png"

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

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

var icons = []target{
	{n: "%s-legacy-ldpi-%vx%v.png", w: 36, h: 36, e: png.Encode},
	{n: "%s-legacy-mdpi-%vx%v.png", w: 48, h: 48, e: png.Encode},
	{n: "%s-legacy-hdpi-%vx%v.png", w: 72, h: 72, e: png.Encode},
	{n: "%s-legacy-xhdpi-%vx%v.png", w: 96, h: 96, e: png.Encode},
	{n: "%s-legacy-xxhdpi-%vx%v.png", w: 144, h: 144, e: png.Encode},
	{n: "%s-legacy-xxhdpi-%vx%v.png", w: 192, h: 192, e: png.Encode},
	{n: "%s-ldpi-%vx%v.png", w: 81, h: 81, e: png.Encode},
	{n: "%s-mdpi-%vx%v.png", w: 108, h: 108, e: png.Encode},
	{n: "%s-hdpi-%vx%v.png", w: 162, h: 162, e: png.Encode},
	{n: "%s-xhdpi-%vx%v.png", w: 216, h: 216, e: png.Encode},
	{n: "%s-xxhdpi-%vx%v.png", w: 324, h: 324, e: png.Encode},
	{n: "%s-xxhdpi-%vx%v.png", w: 432, h: 432, e: png.Encode},
}

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

	img := getSourceImage()

	for _, target := range append([]target{}, icons...) {
		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(baseImage)
	panicOnError(err)

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

	return img
}

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

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

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