Your browser doesn’t support the canvas element.
Specifically, Internet Explorer doesn’t support the canvas element yet. There are some fixes workarounds for that. I’ll come back later and try adding one of those. In addition, some browsers (e.g. FireFox) have problems with the offsetX and offsetY values in the mousemove event. I’m using layerX and layerY on those browsers. That appears to be close, but not quite right.
Anyways, I’m just hacking around with the canvas element to see how hard it is to embed in the blog. I’ll try to do something more interesting with it later.