Bug 213456

Summary: Box with border radius sometimes gets rendered with crossed lines from corners
Product: WebKit Reporter: Paul Gerarts <paulgerarts>
Component: New BugsAssignee: Nobody <webkit-unassigned>
Status: RESOLVED CONFIGURATION CHANGED    
Severity: Minor CC: simon.fraser, webkit-bug-importer, zalan
Priority: P2 Keywords: InRadar
Version: WebKit Nightly Build   
Hardware: Mac   
OS: macOS 10.15   
Attachments:
Description Flags
Block with painting issue none

Description Paul Gerarts 2020-06-22 04:30:02 PDT 
Created attachment 402461 [details]
Block with painting issue

When a block is painted with a border radius it sometimes causes a faint cross (x) to appear from corner to corner. It seems to happen more often on non-retina displays (although it may just be more visible with the reduced density). I can reliably reproduce this in the rendering of this YouTube page on the annotation bubble (the modal that opens on the top-right corner of the video). https://youtu.be/KRGb2s5Ko0Y?t=92 Modal triggers at 01:35 timestamp.

It's not a YouTube issue. This just makes for an example that seems to trigger the issue reliably. I've also had it happen on me while writing CSS. It seems to be a combination of a small border-radius and transparency or opacity.

See the attached image for an example.

I'm running 10.15.5 (19F101) but I've seen this happening on older versions (on a MacBook Pro (Retina, 15-inch, Late 2013) NVIDIA GeForce GT 750M 2 GB, Intel Iris Pro 1536 MB).
Also seen it on a 2019 Touch Bar 4 thunderbolt port 13 inch MacBook Pro without dedicated graphics.
I see it both in Safari Version 13.1.1 (15609.2.9.1.2) and the (at this moment) latest WebKit build (263344).
Again, it's more prevalent on an external monitor (1920 x 1080 in this case).
Comment 1 Paul Gerarts 2020-06-23 02:36:31 PDT 
Perhaps a better example at this site in the search-box in the middle. Again; better visible on a lower density monitor, but it's also definitely there on my Retina display.

https://www.glassdoor.nl/Reviews/index.htm
Comment 2 Radar WebKit Bug Importer 2020-06-23 12:16:42 PDT 
<rdar://problem/64656469>
Comment 3 Simon Fraser (smfr) 2020-06-23 15:14:49 PDT 
Known issue in an underlying graphics framework.
Comment 4 Simon Fraser (smfr) 2020-06-23 20:25:16 PDT 
Please test on macOS Big Sur.