mandelbrot_parallel.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

/* taken from Fractint */

var mandmap = [...][3]byte{
	{255, 255, 255}, {224, 224, 224}, {216, 216, 216}, {208, 208, 208},
	{200, 200, 200}, {192, 192, 192}, {184, 184, 184}, {176, 176, 176},
	{168, 168, 168}, {160, 160, 160}, {152, 152, 152}, {144, 144, 144},
	{136, 136, 136}, {128, 128, 128}, {120, 120, 120}, {112, 112, 112},
	{104, 104, 104}, {96, 96, 96}, {88, 88, 88}, {80, 80, 80},
	{72, 72, 72}, {64, 64, 64}, {56, 56, 56}, {48, 48, 56},
	{40, 40, 56}, {32, 32, 56}, {24, 24, 56}, {16, 16, 56},
	{8, 8, 56}, {000, 000, 60}, {000, 000, 64}, {000, 000, 72},
	{000, 000, 80}, {000, 000, 88}, {000, 000, 96}, {000, 000, 104},
	{000, 000, 108}, {000, 000, 116}, {000, 000, 124}, {000, 000, 132},
	{000, 000, 140}, {000, 000, 148}, {000, 000, 156}, {000, 000, 160},
	{000, 000, 168}, {000, 000, 176}, {000, 000, 184}, {000, 000, 192},
	{000, 000, 200}, {000, 000, 204}, {000, 000, 212}, {000, 000, 220},
	{000, 000, 228}, {000, 000, 236}, {000, 000, 244}, {000, 000, 252},
	{000, 4, 252}, {4, 12, 252}, {8, 20, 252}, {12, 28, 252},
	{16, 36, 252}, {20, 44, 252}, {20, 52, 252}, {24, 60, 252},
	{28, 68, 252}, {32, 76, 252}, {36, 84, 252}, {40, 92, 252},
	{40, 100, 252}, {44, 108, 252}, {48, 116, 252}, {52, 120, 252},
	{56, 128, 252}, {60, 136, 252}, {60, 144, 252}, {64, 152, 252},
	{68, 160, 252}, {72, 168, 252}, {76, 176, 252}, {80, 184, 252},
	{80, 192, 252}, {84, 200, 252}, {88, 208, 252}, {92, 216, 252},
	{96, 224, 252}, {100, 232, 252}, {100, 228, 248}, {96, 224, 244},
	{92, 216, 240}, {88, 212, 236}, {88, 204, 232}, {84, 200, 228},
	{80, 192, 220}, {76, 188, 216}, {76, 180, 212}, {72, 176, 208},
	{68, 168, 204}, {64, 164, 200}, {64, 156, 196}, {60, 152, 188},
	{56, 144, 184}, {52, 140, 180}, {52, 132, 176}, {48, 128, 172},
	{44, 120, 168}, {40, 116, 160}, {40, 108, 156}, {36, 104, 152},
	{32, 96, 148}, {28, 92, 144}, {28, 84, 140}, {24, 80, 136},
	{20, 72, 128}, {16, 68, 124}, {16, 60, 120}, {12, 56, 116},
	{8, 48, 112}, {4, 44, 108}, {000, 36, 100}, {4, 36, 104},
	{12, 40, 108}, {16, 44, 116}, {24, 48, 120}, {28, 52, 128},
	{36, 56, 132}, {40, 60, 140}, {48, 64, 144}, {52, 64, 148},
	{60, 68, 156}, {64, 72, 160}, {72, 76, 168}, {76, 80, 172},
	{84, 84, 180}, {88, 88, 184}, {96, 92, 192}, {104, 100, 192},
	{112, 112, 196}, {124, 120, 200}, {132, 132, 204}, {144, 140, 208},
	{152, 152, 212}, {164, 160, 216}, {172, 172, 220}, {180, 180, 224},
	{192, 192, 228}, {200, 200, 232}, {212, 212, 236}, {220, 220, 240},
	{232, 232, 244}, {240, 240, 248}, {252, 252, 252}, {252, 240, 244},
	{252, 224, 232}, {252, 208, 224}, {252, 192, 212}, {252, 176, 204},
	{252, 160, 192}, {252, 144, 184}, {252, 128, 172}, {252, 112, 164},
	{252, 96, 152}, {252, 80, 144}, {252, 64, 132}, {252, 48, 124},
	{252, 32, 112}, {252, 16, 104}, {252, 000, 92}, {236, 000, 88},
	{228, 000, 88}, {216, 4, 84}, {204, 4, 80}, {192, 8, 76},
	{180, 8, 76}, {168, 12, 72}, {156, 16, 68}, {144, 16, 64},
	{132, 20, 60}, {124, 20, 60}, {112, 24, 56}, {100, 24, 52},
	{88, 28, 48}, {76, 32, 44}, {64, 32, 44}, {52, 36, 40},
	{40, 36, 36}, {28, 40, 32}, {16, 44, 28}, {20, 52, 32},
	{24, 60, 36}, {28, 68, 44}, {32, 76, 48}, {36, 88, 56},
	{40, 96, 60}, {44, 104, 64}, {48, 112, 72}, {52, 120, 76},
	{56, 132, 84}, {48, 136, 84}, {40, 144, 80}, {52, 148, 88},
	{68, 156, 100}, {80, 164, 112}, {96, 168, 124}, {108, 176, 136},
	{124, 184, 144}, {136, 192, 156}, {152, 196, 168}, {164, 204, 180},
	{180, 212, 192}, {192, 220, 200}, {208, 224, 212}, {220, 232, 224},
	{236, 240, 236}, {252, 248, 248}, {252, 252, 252}, {252, 252, 240},
	{252, 252, 228}, {252, 252, 216}, {248, 248, 204}, {248, 248, 192},
	{248, 248, 180}, {248, 248, 164}, {244, 244, 152}, {244, 244, 140},
	{244, 244, 128}, {244, 244, 116}, {240, 240, 104}, {240, 240, 92},
	{240, 240, 76}, {240, 240, 64}, {236, 236, 52}, {236, 236, 40},
	{236, 236, 28}, {236, 236, 16}, {232, 232, 0}, {232, 232, 12},
	{232, 232, 28}, {232, 232, 40}, {236, 236, 56}, {236, 236, 68},
	{236, 236, 84}, {236, 236, 96}, {240, 240, 112}, {240, 240, 124},
	{240, 240, 140}, {244, 244, 152}, {244, 244, 168}, {244, 244, 180},
	{244, 244, 196}, {248, 248, 208}, {248, 248, 224}, {248, 248, 236},
	{252, 252, 252}, {248, 248, 248}, {240, 240, 240}, {232, 232, 232}}

func writeImage(width, height uint, image []byte) {
	w := bufio.NewWriter(os.Stdout)
	defer w.Flush()

	fmt.Fprintln(w, "P3")
	fmt.Fprintf(w, "%d %d\n", width, height)
	fmt.Fprintln(w, "255")

	for i := 0; i < len(image); {
		r := image[i]
		i++
		g := image[i]
		i++
		b := image[i]
		i++
		fmt.Fprintf(w, "%d %d %d\n", r, g, b)
	}
}

func calcMandelbrot(width, height, maxiter uint, palette [][3]byte, image []byte, cy float64, done chan bool) {
	var cx float64 = -2.0
	for x := uint(0); x < width; x++ {
		var zx float64
		var zy float64
		var i uint
		for i < maxiter {
			zx2 := zx * zx
			zy2 := zy * zy
			if zx2+zy2 > 4.0 {
				break
			}
			zy = 2.0*zx*zy + cy
			zx = zx2 - zy2 + cx
			i++
		}
		color := palette[i]
		image[3*x] = color[0]
		image[3*x+1] = color[1]
		image[3*x+2] = color[2]
		cx += 3.0 / float64(width)
	}
	done <- true
}

func main() {
	if len(os.Args) < 4 {
		println("usage: ./mandelbrot width height maxiter")
		os.Exit(1)
	}

	width, err := strconv.Atoi(os.Args[1])
	if err != nil {
		fmt.Printf("Improper width parameter: '%s'\n", os.Args[1])
		os.Exit(1)
	}

	height, err := strconv.Atoi(os.Args[2])
	if err != nil {
		fmt.Printf("Improper height parameter: '%s'\n", os.Args[2])
		os.Exit(1)
	}

	maxiter, err := strconv.Atoi(os.Args[3])
	if err != nil {
		fmt.Printf("Improper maxiter parameter: '%s'\n", os.Args[3])
		os.Exit(1)
	}

	done := make(chan bool, height)

	image := make([]byte, width*height*3)
	offset := 0
	delta := width * 3

	var cy float64 = -1.5
	for y := 0; y < height; y++ {
		go calcMandelbrot(uint(width), uint(height), uint(maxiter), mandmap[:], image[offset:offset+delta], cy, done)
		offset += delta
		cy += 3.0 / float64(height)
	}
	for i := 0; i < height; i++ {
		<-done
	}
	writeImage(uint(width), uint(height), image)
}