Bug 48529 – Assert in FrameView::paintContents if Tiled backing store is used.

• Component: Layout and Rendering
• Status: RESOLVED DUPLICATE

[Viatcheslav Ostapenko]

QtTestBrowser (and, I think, other browsers using tiled backing store implementation) assert in FrameView::paintContents (on ASSERT(!needsLayout());) if tiled backing store enabled with this call stack:

0	WebCore::FrameView::paintContents	FrameView.cpp	1975	0x01cff399	
1	WebCore::Frame::tiledBackingStorePaint	Frame.cpp	856	0x01cf2d69	
2	WebCore::Tile::updateBackBuffer	TileQt.cpp	123	0x01fa337a	
3	WebCore::TiledBackingStore::updateTileBuffers	TiledBackingStore.cpp	117	0x01d72445	
4	WebCore::TiledBackingStore::tileBufferUpdateTimerFired	TiledBackingStore.cpp	366	0x01d73a23	
5	WebCore::Timer<WebCore::TiledBackingStore>::fired	Timer.h	98	0x01d77508	
6	WebCore::ThreadTimers::sharedTimerFiredInternal	ThreadTimers.cpp	112	0x01dc0602	
7	WebCore::ThreadTimers::sharedTimerFired	ThreadTimers.cpp	90	0x01dc0549	
8	WebCore::SharedTimerQt::timerEvent	SharedTimerQt.cpp	116	0x01fafedc	
9	QObject::event	qobject.cpp	1175	0x0445e924	
10	QApplicationPrivate::notify_helper	qapplication.cpp	4396	0x03837c3c	
11	QApplication::notify	qapplication.cpp	3798	0x0383ec6e	
12	QCoreApplication::notifyInternal	qcoreapplication.cpp	732	0x0444b99b	
13	QCoreApplication::sendEvent	qcoreapplication.h	215	0x0447d686	
14	QTimerInfoList::activateTimers	qeventdispatcher_unix.cpp	602	0x0447d686	
15	timerSourceDispatch	qeventdispatcher_glib.cpp	184	0x0447a504	
16	g_main_context_dispatch	/lib/libglib-2.0.so.0	0	0x04e575e5	
17	??	/lib/libglib-2.0.so.0	0	0x04e5b2d8	
18	g_main_context_iteration	/lib/libglib-2.0.so.0	0	0x04e5b4b8	
19	QEventDispatcherGlib::processEvents	qeventdispatcher_glib.cpp	415	0x0447a1f5	
20	QGuiEventDispatcherGlib::processEvents	qguieventdispatcher_glib.cpp	204	0x038f5225	
...	<More>				

If assert is removed, than garbage appears on tiles because they are not getting painted by FrameView::paintContents .

To reproduce, start QtTestBrowser, start loading some big page (http://dpreview.com, for example) and scroll it up and down to invoke tile updates. Asserts come randomly in debug build.

[Viatcheslav Ostapenko]

Created attachment 72205 [details]
Proposed fix.

[Viatcheslav Ostapenko]

Comment on attachment 72205 [details]
Proposed fix.

Doesn't really fix the problem, but somehow hides it a bit, but still reproducible.

[alan]

i think, it is a duplicate of this https://bugs.webkit.org/show_bug.cgi?id=32381
and thus the proposed fix is really just hiding the problem.

[Viatcheslav Ostapenko]

(In reply to comment #3)
> i think, it is a duplicate of this https://bugs.webkit.org/show_bug.cgi?id=32381
> and thus the proposed fix is really just hiding the problem.

Thanks Zalan. It's really dupplicate.
Also, tiled backing store enforces layout before tile update, so it worked fine before, when layout was really doing it's job.
But I have a question - why do we enforce layout? Isn't it better to wait until layout will be completed? Enforcing layout breaks layout throttling and can affect loading performance.

[Viatcheslav Ostapenko]

*** This bug has been marked as a duplicate of bug 32381 ***