draw.go

package main

import (
	"image"
	"image/color"
	"image/draw"
	"image/jpeg"
	"os"
)

func HLine(img draw.Image, x1, y, x2 int, col color.Color) {
	for ; x1 <= x2; x1++ {
		img.Set(x1, y, col)
		img.Set(x1, y+1, col)
		img.Set(x1, y+2, col)
	}
}

func VLine(img draw.Image, x, y1, y2 int, col color.Color) {
	for ; y1 <= y2; y1++ {
		img.Set(x, y1, col)
		img.Set(x+1, y1, col)
		img.Set(x+2, y1, col)
	}
}

func Rect(img draw.Image, x1, y1, w, h int, col color.Color) {
	HLine(img, x1, y1, x1+w, col)
	HLine(img, x1, y1+h, x1+w, col)
	VLine(img, x1, y1, y1+h, col)
	VLine(img, x1+w, y1, y1+h, col)
}

func drawBoxes(fname string, x float32, y float32, w float32, h float32) error {
	f, err := os.Open(fname)
	if err != nil {
		return err
	}
	defer f.Close()
	img, _, err := image.Decode(f)
	if err != nil {
		return err
	}

	b := img.Bounds()
	dst := image.NewRGBA(image.Rect(0, 0, b.Dx(), b.Dy()))
	draw.Draw(dst, b, img, b.Min, draw.Src)
	col := color.RGBA{255, 0, 0, 128}

	// HLine(dst, 10, 200, 200, col)

	// for i := 0; i < 4; i++ {
	Rect(dst, int(float32(b.Dx())*x), int(float32(b.Dy())*y), int(float32(b.Dx())*w), int(float32(b.Dy())*h), col)
	// }
	f.Close()
	f, err = os.Create(fname)
	if err != nil {
		return err
	}
	defer f.Close()

	opt := jpeg.Options{
		Quality: 100,
	}
	err = jpeg.Encode(f, dst, &opt)
	if err != nil {
		return err
	}
	return nil
}