[whatwg] createImageData should take unsigned long

[Boris Zbarsky]

Philip Jägenstedt wrote:
> I wasn't involved then, but I can only presume that there was no 
> perceived benefit of high-DPI ImageData since you can get high-quality 
> rendering just as well with techniques that don't rely on the canvas 
> being higher resolution than the display device.

To be clear, in this context "high-DPI" means "using the DPI of the 
display device, instead of the about 96dpi you get with CSS pixels".

So if this were done and I have a 300-dpi screen, there would be, say, 3 
imagedata pixels per CSS pixel.  If you have a 200-dpi screen, then on 
our computer there would be 2 imagedata pixels per CSS pixel.  Script 
would have to be able to deal with this, which is where the APIs like 
createImageData(imageData) come in.

-Boris