[whatwg] [canvas] request for {create, get, put}ImageDataHD and ctx.backingStorePixelRatio

[Charles Pritchard]

On 3/20/12 3:36 PM, Glenn Maynard wrote:
> On Tue, Mar 20, 2012 at 2:08 PM, Boris Zbarsky<bzbarsky at mit.edu>  wrote:
>
>> That would indeed be very nice.  The question is what happens if drawing
>> happens after the getImageData call...  Or for that matter after the
>> putImageData call (though I suspect there's less need for putImageData to
>> be async).
>>
> The drawing calls that happen after would need to be buffered (or otherwise
> flush the queue, akin to calling glFinish), so the operations still happen
> in order.

Webkit did land buffered drawing operations.

When working with Flash (way back when) as a Canvas polyfill, buffered 
drawing made a huge difference. I doubt it has much of a performance 
impact now, except when rendering is done on some high latency pipeline 
(such as, perhaps, the GPU).

The frustrating item here; the area where there may be a clear 
optimization or win is with video/webcam.

We have to do: drawImage(video).getImageData() for each frame [of 
interest]. That one would be nice to have optimized.

We can't use RoC's media stream processing API (workers) because it's 
for output, not input. We don't need the canvas to keep a copy of the 
image in buffer after the getImageData call.

Beyond that case though, I doubt there's much to be done here

-Charles