bresenham line algorithm

bresenham_line.go

package main

import (
	"image"
	"image/color"
	"image/png"
	"os"
)

func line(img *image.RGBA, x1, y1, x2, y2 int, color color.Color, mirror bool) {
	dx, dy := x2-x1, y2-y1

	if dx < 0 {
		dx = -dy
	}
	if dy < 0 {
		dy = -dy
	}

	d := 2*dy - dx
	incrE := 2 * dy
	incrNE := 2 * (dy - dx)

	for x, y := x1, y1; x <= x2; x++ {
		if mirror {
			img.Set(y, x, color)
		} else {
			img.Set(x, y, color)
		}

		if d <= 0 {
			d += incrE
		} else {
			d += incrNE

			if y1 < y2 {
				y++
			} else if y1 > y2 {
				y--
			}
		}
	}

}

func drawLine(img *image.RGBA, x1, y1, x2, y2 int, color color.Color) {
	if x1 > x2 {
		x1, x2 = x2, x1
		y1, y2 = y2, y1
	}

	dx, dy := x2-x1, y2-y1
	if dy < 0 {
		dy = -dy
	}

	if dy > dx {
		line(img, y1, x1, y2, x2, color, true)
	} else {
		line(img, x1, y1, x2, y2, color, false)
	}
}

func main() {
	width := 1000
	height := 500
	density := 10

	blue := color.RGBA{0, 0, 255, 0xff}
	red := color.RGBA{255, 0, 0, 0xff}
	green := color.RGBA{0, 255, 0, 0xff}
	black := color.RGBA{0, 0, 0, 0xff}

	upLeft := image.Point{0, 0}
	lowRight := image.Point{width, height}
	img := image.NewRGBA(image.Rectangle{upLeft, lowRight})

	for i := 0; i < width; i++ {
		for j := 0; j < height; j++ {
			img.Set(i, j, black)
		}
	}

	for i := 1000; i > 0; i -= density {
		drawLine(img, width, 0, 0, i, red)
		drawLine(img, 0, height, width, i, green)
		drawLine(img, 0, 0, i, height, blue)
	}

	f, _ := os.Create("image.png")
	_ = png.Encode(f, img)
}