[whatwg] Hardware accelerated canvas
chuck at jumis.com
Tue Sep 4 22:38:38 PDT 2012
On 9/4/2012 10:12 PM, Rik Cabanier wrote:
> Rereading the mail thread, it seems like most people want/can live with a
> callback that informs the developer that the canvas needs to be recreated.
Wouldn't this be more appropriate as a "webgl-2d" extension?
It seems like webgl support is a prerequisite for this kind of work.
If we are going to go down this route, I would like to reiterate my
low memory condition events, reporting of the Microsoft window.screen
extensions (for pixel ratios)
and a consideration of on-screen magnification as a reason for
requesting a per-canvas re-paint.
The latter would be pretty cool to have supported as a UA feature.
Currently, authors can zoom in with browser zoom (thus the window.screen
extensions + window.onresize).
I'd love to see magnification added on as well. That's something that we
do see at the OS-level, where the user zooms in on a particular portion
of the screen and moves around.
With a per-canvas repaint request, as authors, we could listen for that
event, and the UA would simply have a transformation matrix appropriate
to the user's zoom level.
With some consideration of low memory conditions (and perhaps media
stream processing), we might have more incentive as authors to want to
hook into these APIs.
I came across the low-memory issue while working on a very memory hungry
application on the iPhone. At some point, I had to do my own memory
management and estimation
to keep from running out of RAM (at which point, iOS terminates the
This whole cluster of use-case has been brought up before on these
lists. If those cases are taken into account, I think it makes a lot
more sense to accommodate this hypothetical lost-context issue.
Otherwise, this does just seem like "webgl-2d".
As for performance: nobody has touched the obvious items, like using
array buffers to describe scenes, instead of using thousands of method
It's a hell of a lot better to upload a float16 array of x/y coordinates
than to run a thousands of drawImage calls (for something like the IE
I'm asking that, if we're going to take the plunge, we go one way or the
other. Satisfy this broad range of real-world uses for canvas 2d,
or go the other route, and think about a webgl-2d, which authors could
select when doing getContext().
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