[whatwg] Hardware accelerated canvas
emoller at opera.com
Sun Sep 2 02:05:49 PDT 2012
As we hardware accelerate the rendering of <canvas>, not just with the
webgl context, we have to figure out how to best handle the fact that GPUs
loose the rendering context for various reasons. Reasons for loosing the
context differ from platform to platform but ranges from going into
power-save mode, to internal driver errors and the famous long running
A lost context means all resources uploaded to the GPU will be gone and
have to be recreated. For canvas it is not impossible, though IMO
prohibitively expensive to try to automatically restore a lost context and
guarantee the same behaviour as in software.
The two options I can think of would be to:
a) read back the framebuffer after each draw call.
b) read back the framebuffer before the first draw call of a "frame" and
build a display list of all other draw operations.
Neither seem like a particularly good option if we're looking to actually
improve on canvas performance. Especially on mobile where read-back
performance is very poor.
The WebGL solution is to fire an event and let the js-implementation deal
with recovering after a lost context
My preferred option would be to make a generic context lost event for
canvas, but I'm interested to hear what people have to say about this.
For reference (since our own BTS isn't public yet).
Core Gfx Lead
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