Closed Bug 1477625 Opened 2 years ago Closed 2 years ago

Text clipping with WebRender on


(Core :: Graphics: WebRender, defect, P1)

Windows 10



Tracking Status
firefox-esr52 --- unaffected
firefox-esr60 --- unaffected
firefox61 --- unaffected
firefox62 --- disabled
firefox63 --- disabled
firefox64 --- fixed


(Reporter: Fanolian+BMO, Assigned: lsalzman)


(Blocks 2 open bugs, )


(Keywords: regression, reproducible)


(3 files)

Attached image WebRender text clipping
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:63.0) Gecko/20100101 Firefox/63.0
Build ID: 20180722220044

Steps to reproduce:
0. Set gfx.webrender.all to true. Restart browser.
1. Visit
2. Observe the text near the top of the page.

Actual result:
The last digit is clipped (Please see attachment).

Additional information:
There is no clippings with WebRender off.
The issue does not occur at every Nightly's zoom levels. It is most obvious at 67%, 100%, and 150%.

Font used in the screenshot (which is the default):
Segoe UI Bold, 13px, weight 700.

Mozregression points to bug 1463416.
Blocks: 1463416
Has Regression Range: --- → yes
Has STR: --- → yes
The issue also occurs at Google Calendar using Month View, but only with some tiles.
The last f in the tiles "Day off" is clipped.
Ever confirmed: true
Flags: needinfo?(lsalzman)
OS: Unspecified → Windows 10
Version: 62 Branch → Trunk
Not sure. I found the same Win10 regression range as the reporter, but couldn't really reproduce bug 1464371 (Linux).
I thought that this could be a regression of bug 1458921 which landed together with bug 1463416.
Priority: -- → P1
lee has been able to reproduce this and is looking into it
Assignee: nobody → lsalzman
I'd love a fix for this (especially since Lee can repro), but we can let this ride to beta.
Priority: P1 → P2
It sounds like this is a pretty noticeable problem that can be annoying. I'm upgrading to P1. I don't want to block nightly on this but hopefully it will be ready today anyways.
Priority: P2 → P1
WR PR will partially fix the clipping issue. A Gecko-side patch coming shortly will fix another part of this.
Flags: needinfo?(lsalzman)
When rendering in GDI mode, we're getting rounding of glyph positions that is screwing up all the positioning completely. With Skia, we were actually disabling subpixel positioning for GDI mode, so we need to do that with WR as well.
Attachment #9008474 - Flags: review?(jmuizelaar)
Attachment #9008474 - Flags: review?(jmuizelaar) → review+
Pushed by
Don't use subpixel positioning for GDI fonts in WebRender. r=jrmuizel
Closed: 2 years ago
Resolution: --- → FIXED
Target Milestone: --- → mozilla64
Depends on: 1491130
See Also: → 1464371
Depends on: 1508203
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