Markus Stange [:mstange] Assignee
	Description • 7 years ago

Steps to reproduce:

0. Be on Mac and use the default theme with vibrancy in the tab bar.
1. Open a new window and move / resize it so that its tab bar is on top of something bright.
2. Load the attached image in a tab of that window.
3. Pin the tab with the image.
4. Open two more tabs.
5. Move your mouse over the second tab (the unselected tab in the middle, next to the pinned tab.)

Observe how the white circle changes its brightness as you hover the tab.

	Markus Stange [:mstange] Assignee
	Comment 1 • 7 years ago

I think this happens because we're using a component alpha layer for the tab bar. But the tab bar is over transparency, and component alpha compositing into transparent pixels gives incorrect results. We should be disabling component alpha for layers in the browser chrome; we have code that's supposed to take care of that (e.g. nsDisplayListBuilder::NeedToForceTransparentSurfaceForItem) but apparently it's not taking effect.

	Markus Stange [:mstange] Assignee
	Comment 2 • 7 years ago

This seems to be a regression from bug 1359584.

	Miko Mynttinen
	Comment 4 • 7 years ago
mozreview-review

Comment on attachment 8909959 [details]
Bug 1401037 - Propagate nsDisplayList::mForceTransparentSurface to the parent list when recursing into flattened items.

https://reviewboard.mozilla.org/r/181438/#review186692

	Miko Mynttinen
	Comment 5 • 7 years ago

Can we combine this propagation with the one later in the code?
http://searchfox.org/mozilla-central/rev/1c13d5cf85f904afb8976c02a80daa252b893fca/layout/painting/FrameLayerBuilder.cpp#4511

	Pulsebot
	Comment 6 • 7 years ago

Pushed by mstange@themasta.com:
https://hg.mozilla.org/integration/autoland/rev/847a0c0530a5
Propagate nsDisplayList::mForceTransparentSurface to the parent list when recursing into flattened items. r=miko

	Markus Stange [:mstange] Assignee
	Comment 7 • 7 years ago

Too late! :)

Hmm, I don't think we can, at least not easily. This flag gets set on the list once we encounter an item that requires a transparent surface, so the propagation needs to happen *after* we've iterated over all the items in the sublist.

	Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)
	Comment 8 • 7 years ago
bugherder

https://hg.mozilla.org/mozilla-central/rev/847a0c0530a5

	Eddward
	Comment 9 • 7 years ago

I can confirm that this fixed the favicon flickering for me when hovering over the tabs as showed here:
https://bugzilla.mozilla.org/show_bug.cgi?id=1387296#c21