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Re: [Public WebGL] More predictable behavior for !preserveDrawingBuffer
On Mon, Jun 4, 2012 at 6:50 PM, Kenneth Russell <email@example.com>
This question has been raised before; see
for example. Please check the archives, and see if there's new
information or thoughts on topic.
That's a different question.Â I already know how to handle the issue of when to trigger the clear (or at least I think I do).Â I'll post that in detail, but the first question is whether the triple-buffering approach itself is implementable.
On Mon, Jun 4, 2012 at 6:54 PM, James Robinson <firstname.lastname@example.org>
preserveDrawingBuffer is false, the buffer is cleared when it's
actually composited.Â Would it be possible to clear the buffer as soon
as the JS code returns to the browser, rather than waiting for
compositing, so the time of compositing can't affect script behavior?
These times aren't quite the same. ÂFor instance:
know.Â I have
demonstrates one of the problems that needs to be fixed; on my system,
it alternately displays 4294902015/4294902015 and 4294902015/0,
depending on when compositing happens.
The point here is that the
script-visible part--the clearing of the buffer--would happen
immediately, and synchronously, when you return from JS to the browser.Â
In principle, that would simply be a triple buffer flip, handing the
buffer you just drew to the compositor and giving you an empty
buffer immediately.Â In practice I'm guessing it's a bit more
complicated than that, since you can't flip the buffer until the drawing
queue finishes, and you don't want to block the UI thread or script
execution while you effectively do a glFinish().Â That's the part I'm
not sure about the practicality of...
this test case, while the modal dialog is open I see a blue square in
the most recent versions of Chrome and Firefox, indicating that the
browser did in fact composite even though the anonymous function has not
yet returned control to the browser and the task queue is suspended.
ÂYou'll have to pretty carefully define when exactly you want the
clearing to happen to make this proposal well-defined.
That work is already done for us; see the "stable state" concept in HTML.
I already have suggested text using it, but I wanted to check this underlying question first, so I don't waste people's time if it's just not implementable.)