Creating mandelbrot, one pixel at a time

mandelbrot.go

package main

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

func main() {
	width := flag.Int("width", 1024, "width of the image in pixels")
	height := flag.Int("height", 1024, "height of the image in pixels")
	out := flag.String("out", "out.png", "name for the output PNG file")
	flag.Parse()

	m := create(*width, *height)

	f, err := os.Create(*out)
	if err != nil {
		log.Fatalf("could not create image: %v", err)
	}
	if err := png.Encode(f, m); err != nil {
		log.Fatalf("could not encode image: %v", err)
	}
	if err := f.Close(); err != nil {
		log.Fatalf("could not write file: %v", err)
	}
}

func create(width, height int) image.Image {
	m := image.NewRGBA(image.Rect(0, 0, width, height))

	for i := 0; i < width; i++ {
		for j := 0; j < height; j++ {
			fillPixel(m, i, j)
		}
	}

	return m
}

func fillPixel(m *image.RGBA, i, j int) {
	b := m.Bounds()
	// normalized from -2.5 to 1
	xi := 3.5*float64(i)/float64(b.Dx()) - 2.5
	// normalized from -1 to 1
	yi := 2*float64(j)/float64(b.Dy()) - 1

	const maxI = 1000
	x, y := 0., 0.
	for i := 0; (x*x+y*y < 4) && i < maxI; i++ {
		x, y = x*x-y*y+xi, 2*x*y+yi
	}

	c := byte(x * y)
	m.Set(i, j, &color.RGBA{c, c, c, 255})
}