Bug 154069 – [Threaded Compositor] Flickering when zooming in/out in maps.google.com

• Status: RESOLVED
• Resolution: FIXED
• Component: WebKit2

[Carlos Garcia Campos]

Open maps.google.com and zoom in/out with the mouse scroll wheel, you see flickering.

[Carlos Garcia Campos]

I've built with accelerated 2d canvas disabled, and the result is the same. Flickering when zooming and text sometimes disappear, even the background is sometimes fully back.

[Carlos Garcia Campos]

And the same with the redirected X window disabled.

[Carlos Garcia Campos]

Disabling WebGL in MiniBrowser settings fixes the issue, so I guess it's a problem with the threaded compositor and WebGL.

[Miguel Gomez]

The problem here is that the webgl frames are rendered faster than they are composited.
As we only have 2 buffers in GraphicsContext3D to hold the rendered frames, sometimes a buffer is reused for rendering when it hasn't been composited yet (or while it's being composited), and this causes the flickering.

I'll attach a patch that fixes this by using one extra buffer to hold the renderings. This removes the flicker issues.

But at some point we should add a general solution (also for the acc canvas) that somehow blocks the renderings when there are no buffers available.

[Miguel Gomez]

Created attachment 283008 [details]
Patch

[Carlos Garcia Campos]

(In reply to comment #4)
> The problem here is that the webgl frames are rendered faster than they are
> composited.
> As we only have 2 buffers in GraphicsContext3D to hold the rendered frames,
> sometimes a buffer is reused for rendering when it hasn't been composited
> yet (or while it's being composited), and this causes the flickering.
> 
> I'll attach a patch that fixes this by using one extra buffer to hold the
> renderings. This removes the flicker issues.
> 
> But at some point we should add a general solution (also for the acc canvas)
> that somehow blocks the renderings when there are no buffers available.

If at some point this is the only blocker to enable the threaded compositor, I prefer to land this to fix the issue. We can always improve it later.

[Carlos Garcia Campos]

Comment on attachment 283008 [details]
Patch

Let's land this for now, thanks Miguel! File new bug reports for any improvements you might want to do.

[WebKit Commit Bot]

Comment on attachment 283008 [details]
Patch

Clearing flags on attachment: 283008

Committed r203498: <http://trac.webkit.org/changeset/203498>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.