Hi everyone, looking for help :-)

[Dorkside]

Hey there,
I've recently decided to build a website based on html5 canvases, and managing not so bad until I realised I needed multiple canvases to induce a zIndex system so as to reduce CPU charge while executing the page.
Therefore I recoded my whole script, in a very bulky way for some parts, but as a first version of the code that didn't seem too important.
I just can't manage to determine what is wrong with my sourcecode.
If anyone has time and could throw an eye on it, I would be most grateful.
Any kind of advice is welcome.