Golang Image Square Resize

main.go

package main

import (
	"flag"
	"fmt"
	"image"
	"image/draw"
	"image/png"
	"os"
	"path/filepath"
)

var (
	dir string
)

func init() {
	flag.StringVar(&dir, "dir", ".", "directory to read")
	flag.Parse()
}

func main() {
	entries, err := os.ReadDir(dir)
	if err != nil {
		panic(err)
	}

	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}

		ext := filepath.Ext(entry.Name())
		if ext != ".png" {
			continue
		}
		fileName := filepath.Base(entry.Name())
		baseName := fileName[:len(fileName)-len(ext)]

		f, err := os.Open(filepath.Join(dir, entry.Name()))
		if err != nil {
			panic(err)
		}
		defer f.Close()

		img, _, err := image.Decode(f)
		if err != nil {
			panic(err)
		}

		bounds := img.Bounds()
		w := bounds.Dx()
		h := bounds.Dy()

		if w == h {
			continue
		}

		var (
			resizedImg *image.RGBA
			point      image.Point
		)
		if w > h {
			resizedImg = image.NewRGBA(image.Rect(0, 0, w, w))
			point = image.Point{0, -(w - h) / 2}
		} else {
			resizedImg = image.NewRGBA(image.Rect(0, 0, h, h))
			point = image.Point{-(h - w) / 2, 0}
		}

		draw.Draw(resizedImg, resizedImg.Bounds(), img, point, draw.Src)

		out, err := os.OpenFile(filepath.Join(dir, fmt.Sprintf("%s_resized%s", baseName, ext)), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
		if err != nil {
			panic(err)
		}
		defer out.Close()
		err = png.Encode(out, resizedImg)
		if err != nil {
			panic(err)
		}
	}
}