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Mousing over <select> elements invalidates an area that is too large




13 years ago
5 years ago


(Reporter: Simon Fraser, Unassigned)



Firefox Tracking Flags

(Not tracked)





13 years ago
When you mouse over a <select> element that displays as a combobox, or a
scrolling list, we invalidate an area that is the size of all the child frames
as if they were visible. This can cause the invalidate to hit other frames,
which may be expensive-to-redraw things like plugins etc.

The reason seems to be some code in UpdateViewsForTree() (in
nsCSSFrameConstuctor) that naively walks the child frames of the frame whose
state has changed (the combobox frame), doing a union of the bounds of the child

In the case of combox boxes, those child frames might not be visble, either
because their containing view (the dropdown) is hidden, or because they are part
of a scrolling view, and scrolled out of view.
Solving the case when we're clipped by a scrollframe could be tough...  But
shouldn't we just ignore invalidates on views that are hidden?  In particular, I
think we should bail out of nsViewManager::UpdateView if the view is hidden, and
when doing UpdateViewsForTree we should only do out-of-flows after we hit a
hidden view (I _think_ that should be ok, right?).

Alternately, should setting a view's visibility to kHide somehow mark all its
descendant views so we can easily tell that we're in a non-painting subtree?
Yeah, in theory we need not paint any view that is hidden or has a hidden view
We have some code to that effect in nsViewManager::SetViewVisibility, but it
doesn't set the visibility of descendant views with frames.... should it?
I don't think we should recursively change the visibility status of child views.
It's OK for hiding but not when you make the parent view visible again. Instead
we should just check ancestors on the fly when we make visibility decisions.
The problem with checking ancestors is that we're trying to optimize based on
visibility, and checking ancestors may end up more expensive...
View trees are usually quite shallow.
Last Resolved: 5 years ago
Resolution: --- → WORKSFORME
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