title: HTML5 Canvas fillRect slow
body: <p>I'm trying to write a simple raycaster using an HTML5 canvas and I'm getting abysmal framerates.  Firefox's profiler reports 80% of my runtime is spent in context2d.fillRect(), which I'm using per column for floors and ceilings and per pixel on the textured walls.  I came across <a href="https://stackoverflow.com/questions/4899799/whats-the-best-way-to-set-a-single-pixel-in-an-html5-canvas">this</a> question, and found that fillRect was faster than 1x1 px pictures by 40% on chrome and 4% on firefox.  They mention how it's still calculating alpha stuff, although I'd assume if the alpha is 1 it'd have a pass through for opaque rendering?  Are there any other methods for doing a lot of rectangle and pixel blitting with javascript I should try out?</p>