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Re: [Public WebGL] Resurrecting Update Scheduling

On Apr 17, 2010, at 2:26 PM, Jonatan Wallmander wrote:

> Kenneth Russell wrote:
>> Browsers supporting hardware compositing should automatically support
>> vsynced rendering. WebGL never renders directly to the screen; it
>> can't according to the HTML compositing model. If the browser uses a
>> GPU-based API to put the rendering results on the screen, and enables
>> vsync, then the WebGL output will be vsynced. Otherwise it's basically
>> impossible to get it to be.
>> -Ken
> In theory - shouldn't it be possible for browser implementors to optimize their compositing engine
> so that direct rendering can be done in applicable situations?
> Example (pseudocode):
> if all of the following are true:
>  - nothing obscuring the 3d-canvas (no hovering semi-transparent divs etc)
>  - canvas is 100% opaque (style-wise)
>  - not clipped against browser client area
>  - alternative take on the previous condition: if there are scrollbars, always run compositor
> then
> render directly
> else
> render with compositor (software/hardware)
> Thus a canvas scaled to the size or less of the window will always render directly and still not
> break the HTML compositing standard.
> It would really mean an immense performance boost compared to the GPU->CPU->GPU train which
> is abnormally slow considering what the GPU can do.
> I also imagine a hardware compositor can get pretty complex, so would save some (for a game or immersive site)
> unnecesarry CPU cycles.
> It would be very very nice if something like this was implemented.

There are many ways to optimize compositing. It's difficult to apply many of them to the general browser model because of its complexity. But all of them are platform dependent. WebKit already avoids a GPU->CPU copy for WebGL content, so I don't know how much more efficient the optimization you're talking about would be. 

The place I think significant optimizations could be achieved is when running full-screen. If WebGL could be put in full-screen mode, like video can, we could use all kinds of optimizations, including v-sync optimizations. But as I said, that's all platform specific.


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