Visual defect on lowercase "z" in .SF NS Text system font at 19.2px on macOS 10.12




2 years ago
9 months ago


(Reporter: timdream, Unassigned)


52 Branch
Mac OS X

Firefox Tracking Flags

(Not tracked)


(Whiteboard: [gfx-noted], URL)


(2 attachments)

Created attachment 8814282 [details]

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.
Keywords: regressionwindow-wanted
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

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 ?
Keywords: regressionwindow-wanted
(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.


2 years ago
Flags: needinfo?(aschen)
Whiteboard: [gfx-noted]
Submitted a bug via Apple Bug Reporter and bug ID is 29753182.
I'll track the bug and update status here.
Assignee: nobody → aschen
Flags: needinfo?(aschen)
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:


9 months ago
Assignee: bmo → nobody
You need to log in before you can comment on or make changes to this bug.