// Dave Gilbert's parallel mandelbrot.  Inspiration and the odd line of code
// drawn from the mandelbrot bench in the go distrobution
// dave@treblig.org

package main

import (
	"flag";
	"image";
	"image/png";
	"bufio";
	"os";
)

var size = flag.Int("size", 256, "Size of the image")
var left = flag.Float("left", -2.0, "Left extent of brot")
var right = flag.Float("right", 2.0, "Right extent of brot")
var top = flag.Float("top", -2.0, "Top extent of brot")
var bottom = flag.Float("bottom", 2.0, "Bottom extent of brot")
var maxIter = flag.Int("maxIter", 255, "Maximum number of iteractions")

var im *image.RGBA

func doPoint(x, y int, xval, yval float) {
	var tmpcol image.RGBAColor;
	tmpcol.A = 255;

	var Ti, Tr, Zi, Zr float;
	var Ci, Cr float;
	var iter int;

	Cr = xval;
	Ci = yval;

	for iter = 0; (iter <= *maxIter) && (Ti+Tr < 4.0); iter++ {
		// These 4 lines from the C benchmark version
		Zi = 2.0*Zr*Zi + Ci;
		Zr = Tr - Ti + Cr;
		Tr = Zr * Zr;
		Ti = Zi * Zi;
	}

	// Try and get some basic interesting colour
	tmpcol.R = uint8(iter % 256);
	tmpcol.G = uint8((iter & 15 << 4) | ((iter & 240) / 16));
	tmpcol.B = tmpcol.R;
	im.Set(x, y, tmpcol);
}

func doRow(y int, yval float, ack chan bool) {
	for x := 0; x < *size; x++ {
		doPoint(x, y, valInRange(*left, *right, *size, x), yval)
	}

	ack <- true;
}

// Returns a value representing point 'offset' within a range between start and end where there are 'size' points
func valInRange(start, end float, size, offset int) float {
	var ran = end - start;

	return start + (ran*float(offset))/float(size);
}

func main() {
	flag.Parse();

	im = image.NewRGBA(*size, *size);

	donechan := make(chan bool, *size);

	for y := 0; y < *size; y++ {
		go doRow(y, valInRange(*top, *bottom, *size, y), donechan)
	}

	for y := 0; y < *size; y++ {
		<-donechan
	}

	out := bufio.NewWriter(os.Stdout);
	defer out.Flush();

	png.Encode(out, im);
}