HCL Canvas Mandelbrot Explorer

I've written a mandelbrot set explorer for the HTML5 canvas in Hot Cocoa Lisp

Setup

To use the explorer

git clone git@github.com:olleicua/hcl-canvas-mandelbrot.git
open hcl-canvas-mandelbrot/mandelbrot.html in a web browser
use w, a, s, and d to move around, q to zoom in, and e to zoom out

For devs

Install:

npm -g install hot-cocoa-lisp
git clone git@github.com:olleicua/hcl-canvas-mandelbrot.git
cd hcl-canvas-mandelbrot

And compile:

hcl -b mandelbrot.hcl

Optimizations

I'm using two notable optimizations so far:

Only multiply three times per loop

Without this optimization we would have:

While (zr * zr) + (zi * zi) < 4
  zr = (zr * zr) - (zi * zi) + cr
  zi = (2 * zr * zi) + ci

Multiplication is expensive and there are six of them here. Instead I used an optimization I found here: http://randomascii.wordpress.com/2011/08/13/faster-fractals-through-algebra/

zrsqr = zr * zr;
zisqr = zi * zi;
While zrsqr + zisqr < 4
  zi *= zr
  zi += zi
  zi += ci;
  zr = zrsqr – zisqr + cr
  zrsqr = (zr * zr)
  zisqr = (zi * zi)
}

Check for periodic behaviour

I used a technique described here (http://locklessinc.com/articles/mandelbrot/) to check whether the cycle of zs enters a loop and stop immediately if it does rather than continuing on to maxIter

olleicua/hcl-canvas-mandelbrot