Bug 1506508 Comment 29 Edit History

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Original comment by
on 
(In reply to Olli Pettay [:smaug] from comment #28)

> do you know what exactly under ProcessPendingUpdates() call makes this to work? (ProcessPendingUpdates() does so many different things)

A call of [nsViewManager::CallWillPaintOnObservers() in ProcessPendingUpdates()](https://searchfox.org/mozilla-central/rev/c21d6620d384dfb13ede6054015da05a6353b899/view/nsViewManager.cpp#1017,1028) flushes the positioned element as expected.

It just calls [nsIPresShell::WillPaint()](), then, [it makes paint observers in root precContext](https://searchfox.org/mozilla-central/rev/c21d6620d384dfb13ede6054015da05a6353b899/layout/base/nsPresContext.cpp#2963-2970) and calls {FlushPendingNotifications(ChangesToFlush(FlushType::InterruptibleLayout, false));`.

I'm still not sure which observer flushes it.
Revision 1 by
on 
(In reply to Olli Pettay [:smaug] from comment #28)

> do you know what exactly under ProcessPendingUpdates() call makes this to work? (ProcessPendingUpdates() does so many different things)

A call of [nsViewManager::CallWillPaintOnObservers() in ProcessPendingUpdates()](https://searchfox.org/mozilla-central/rev/c21d6620d384dfb13ede6054015da05a6353b899/view/nsViewManager.cpp#1017,1028) flushes the positioned element as expected.

It just calls [nsIPresShell::WillPaint()](), then, [it makes paint observers in root precContext](https://searchfox.org/mozilla-central/rev/c21d6620d384dfb13ede6054015da05a6353b899/layout/base/nsPresContext.cpp#2963-2970) and calls `FlushPendingNotifications(ChangesToFlush(FlushType::InterruptibleLayout, false));`.

I'm still not sure which observer flushes it.

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