Created attachment 8814282 [details] z-defect.png Please see screenshot. There is a thin vertical line that connects the top horizontal line and the bottom angle of z. The MBPR 13" is scaled at "Looks like 1680x1050" and GitHub is full-page-zoomed at 120%.
The computed font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol" And the font inspector says System Font system Used as: ".SF NS Text"
I can reproduce on my MBPR 15" when zooming the page to 120%. Windows 10, Ubuntu 16.04 all looks good with same zooming configuration.
Priority: -- → P3
Hmm, finding regressionwindow on macOS Sierra is very hard because of bug 1284677, so although I can reproduce it, I cannot use mozregression to find the regressionwindow. Hopefully someone still using earlier version of OS X can help.
I don't see the problem on OS X 10.10.
This seems to be specific to the size 19.2px on a Retina screen; I'm guessing it might occur at 38.4px on a non-Retina display, but have not yet tested that. I suspect this may be an Apple font/rasterizer bug rather than a Gecko bug, as I can also reproduce it in Chrome using data:text/html,<div%20style="font:caption;font-size:19.2px">xyzzy I was unable to reproduce it in Safari, but that may be because it seems to snap font sizes to whole (device) pixels.
Summary: Visual defect on small caps "z" on Mac → Visual defect on lowercase "z" in .SF NS Text system font at 19.2px on macOS 10.12
Tested on 10.10 and 10.11, the phenomenon was unable to reproduce. It seems a bug of 10.12. Any suggestions to proceed ?
(In reply to Astley Chen [:astley] (UTC+8) from comment #6) > Tested on 10.10 and 10.11, the phenomenon was unable to reproduce. It seems > a bug of 10.12. I'd assume 10.12 has an updated version of the font, and the glitch is very specific to that exact version. > Any suggestions to proceed ? Given that it reproduces in Chrome as well as Firefox, it may be a font bug (which should be reported to Apple). Another possibility, though, could be a Skia bug (e.g. in glyph caching or something). It's a pity Firefox no longer has any other rendering backend we can try (AFAICT). It might be interesting to try and reproduce the problem in a standalone testcase that just uses Apple rendering APIs, to see if it can occur there.
Ah, never mind Skia - it's definitely an Apple bug (in either the font itself or the font rasterizer). I can reproduce it by rendering "z" in the system font at 19.2pt in a simple Cocoa app, with no extra graphics framework layers involved.
Created attachment 8815236 [details] Screenshot showing the same glitch in Xcode Here's a screenshot of Xcode displaying a simple "label" object set to the System font at size 19.2, and the same rendering glitch occurs.
Submitted a bug via Apple Bug Reporter and bug ID is 29753182. I'll track the bug and update status here.
Assignee: nobody → aschen
Status: NEW → ASSIGNED
Unfortunately, the font issue remains on macOS High Sierra 10.13 GM (17A365). It's been 9 months wait for nothing.
Just contacted an Apple developer via Twitter, and he is looking: https://twitter.com/upsuper/status/912845966062923776
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