Utility to add transparent horizontal stripes to an image.

stripes.go

//
// Add transparent horizontal stripes to an image.
//
// Usage:
//   go run stripes.go image.png 6 12 420
//                     |         | |  |
//                     |         | |  `- top and bottom padding
//                     |         | `---- space between stripes
//                     |         `------ stripes width
//                     `---------------- original file name or path
// Output:
//   image-stripes.png
//

package main

import (
	"fmt"
	"image"
	"image/color"
	"image/draw"
	"image/png"
	"os"
	"path/filepath"
	"strconv"
	"strings"
)

func main() {
	// Parse arguments.

	if len(os.Args) < 5 {
		fmt.Printf("Wrong number of arguments.\nUsage:\n\tgo run stripes.go 10 5 100 image.png\n")
		return
	}

	inputFileName := os.Args[1]
	fmt.Printf("Image name: %s\n", inputFileName)

	stripeWidth, err := strconv.Atoi(os.Args[2])
	if err != nil {
		fmt.Printf("Cannot parse second argument (stripe width, int): %s\n", err)
		return
	}
	fmt.Printf("Stripes width: %d\n", stripeWidth)

	stripeSpacing, err := strconv.Atoi(os.Args[3])
	if err != nil {
		fmt.Printf("Cannot parse third argument (stripe spacing, int): %s\n", err)
		return
	}
	fmt.Printf("Stripes spacing: %d\n", stripeSpacing)

	padding, err := strconv.Atoi(os.Args[4])
	if err != nil {
		fmt.Printf("Cannot parse forth argument (padding, int): %s\n", err)
		return
	}
	fmt.Printf("Padding: %d\n", padding)

	// Open and decode the original image.

	file, err := os.Open(inputFileName)
	if err != nil {
		fmt.Printf("Cannot open file: %s\n", err)
		return
	}
	defer file.Close()

	img, _, err := image.Decode(file)
	if err != nil {
		fmt.Printf("Cannot decode image: %s\n", err)
		return
	}

	// Create and draw on a new image.

	bounds := img.Bounds()
	newImg := image.NewRGBA(bounds)
	draw.Draw(newImg, bounds, img, bounds.Min, draw.Src)

	transparent := color.RGBA{0, 0, 0, 0}

	var y int = padding
	for y < bounds.Max.Y-stripeSpacing-stripeWidth-padding {
		rect := image.Rect(bounds.Min.X, y, bounds.Max.X, y+stripeWidth)
		draw.Draw(newImg, rect, &image.Uniform{transparent}, image.Point{}, draw.Src)
		y += stripeSpacing + stripeWidth
	}

	// Save the new image.

	inputFileExt := filepath.Ext(inputFileName)
	outputFileName := fmt.Sprintf(
		"%s-stripes%s",
		strings.TrimSuffix(filepath.Base(inputFileName), inputFileExt),
		filepath.Ext(inputFileExt),
	)

	outputFile, err := os.Create(outputFileName)
	if err != nil {
		fmt.Printf("Cannot create file: %s\n", err)
		return
	}
	defer outputFile.Close()

	err = png.Encode(outputFile, newImg)
	if err != nil {
		fmt.Printf("Cannot encode file: %s\n", err)
		return
	}
	fmt.Printf("File created: %s\n", outputFileName)

	fmt.Printf("Done.\n")
}