[whatwg] Need clarification on DOM exceptions thrown by canvas 2D drawImage

[Justin Novosad]

>
> It sounds like it would make fast GPU-accelerated blitting difficult, even
> in fairly simple cases.
>

Not that bad.
I can think of two ways:
A) create a cropped texture just for the sub rectangle
B) implement your own clamping in the shader

I think A) is problematic because some platforms do not have
non-power-of-two textures, though that problem is slowly fading away.
Chrome does B)

-Justin