[Bug 85064] modesetting driver plus DRI3 causes extremely slow scrolling with WebKitGTK+ in accelerated compositing mode

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Wed Aug 3 07:15:56 UTC 2016


--- Comment #41 from Michel Dänzer <michel at daenzer.net> ---
(In reply to Carlos Garcia Campos from comment #40)
> Yes, this is because we use the screen width + 1 to position our window
> offscreen:
> WidthOfScreen(screen) + 1, 0, 1, 1,

FWIW, WidthOfScreen is bad anyway because that's just how wide the screen
happened to be when the X11 display connection was established. The screen can
be widened after that via the RandR extension, in which case the window would
become visible.

> and it turns out that simply using -1, -1 as coordinates fixes the problem.

Weird, not sure why that avoids the problem; maybe there's an off-by-one bug
somewhere which causes the window to be incorrectly considered on-screen. I
wouldn't recommend relying on that. Also, again I'm not sure that negative
coordinates can never be visible.

So, why does this code use a window instead of a pixmap?

Assuming a window is really the only possibility, (why) can't it set the swap
interval to 0 via one of the GLX extensions for this, to prevent SwapBuffers
operations from getting throttled?

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