Draws the fractal Sierpinski Triangle on an html5 canvas element via the Chaos Game method.

sierpinski.js

drawflag = false;
i = -10;
maxi = 1000000;

function toggleDraw() {
    button = document.getElementById("button");
    drawflag = !drawflag;
    if (!drawflag) {
        button.innerHTML = "Resume";
    } else {
        button.innerHTML = "Stop";
        canv = document.getElementById("c1");
        c = canv.getContext("2d");
        counter = document.getElementById("ct");
        if (i<=0) {
            x = Math.random()*canv.width | 0;
            y = Math.random()*canv.height | 0;
            p = [x,y];
        }
        equiheight = Math.sqrt(3*canv.height*canv.height/4.);
        equivertices = [[canv.width/2,canv.height/2-equiheight/2],
                        [0,canv.height/2+equiheight/2],
                        [canv.width,canv.height/2+equiheight/2]];
        draw();
    }
}
function draw() {
    if (drawflag) {
        counter.innerHTML = i;
        p = chaosgame(equivertices,p,0.5);
        if (i > 0) { // burn the first few
            c.fillRect(p[0],p[1],1,1);
        }
        i += 1;
        if (i < maxi) {
            setTimeout("draw()",1);
        }
    }
} 
function chaosgame(vertices,p,frac) {
    /*Takes a list of vertices, each vertex
    tuple of the form (x,y), a 2-tuple p of
    the same form, and a floating point frac.
    Randomly selects a vertex and returns
    the point that is the frac fraction of 
    the way between the vertex and point p.
    */
    var v_index = Math.min(Math.floor(Math.random()*vertices.length),vertices.length-1);
    var vertex = vertices[v_index];
    var new_x = (vertex[0] + p[0]) * frac;
    var new_y = (vertex[1] + p[1]) * frac;
    return [new_x,new_y];
}