968201 - White box visible on hovered background tabs Win7

Status: VERIFIED FIXED

(Firefox :: Theme, defect)

Description

[Jim Jeffery not reading bug-mail 1/2/11]

Attachment: tabwhitelines.jpg

See attached.  I'm seeing a faint white-box on background tabs when hovered.  I am suspecting bug 878023 is responsible. 

Tested on win7 x64 m-c tinderbox build:

Good cset:  https://hg.mozilla.org/mozilla-central/rev/1f170f9fead0
bad cset:   https://hg.mozilla.org/mozilla-central/rev/8f7033c595b9

Comment 1

[Markus Stange [:mstange]]

Uhh...

Comment 2

[Markus Stange [:mstange]]

I don't really have the time to debug this on Windows now, so I'll back out bug 878023. :(

Comment 3

[Markus Stange [:mstange]]

So this is actually reproducible on Mac, too, by setting layout.css.devPixelsPerPx to 1.1 and gfx.hidpi.enabled to 0.

I debugged this a bit and it looks like this is caused by border-width snapping. If I replace the definition of NS_ROUND_BORDER_TO_PIXELS(l,tpp) in nsStyleStruct.h with just (l), the bug goes away. (But we can't do that.)

The borders that are at fault here are those on .tab-background-middle:
border-left: @tabCurveHalfWidth@ solid transparent;
border-right: @tabCurveHalfWidth@ solid transparent;
Replacing them by paddings and using background-clip:content-box instead of border-box fixes this bug, too, but we can't do that because we already need background-clip:context-box together with padding-top for additional clipping of the background color of the selected tab.

I'm out of ideas for the moment.

Comment 4

[Dão Gottwald [:dao]]

fixed by backing out bug 878023

Comment 5

[Paul Silaghi, QA [:pauly]]

Reproduced when setting layout.css.devPixelsPerPx to 1.1 on Nightly 2014-02-06, Win 7 x64.
Verified fixed FF 31.0a1 (2014-03-18).

Comment 6

[Paul Silaghi, QA [:pauly]]

(In reply to Paul Silaghi, QA [:pauly] from comment #5)
> Verified fixed FF 31.0a1 (2014-03-18).
Actually I meant FF 30.0a1 (2014-03-17)