[Linux/FreeType + VariableTTF-specific] Some glyphs (e.g. a '4', or the bottom-right stem of lowercase 'u') look weird at certain sizes, due to mis-handling overlapping paths of variable font. Needs FreeType 2.10.3 and font flag OVERLAP_{SIMPLE, COMPOUND}

[ronjouch]

Environment

Cascadia Code version number: 2008.25
Application used to display text: VS Code 1.48.2, Firefox 80.0, Kitty 0.18.3, everywhere
OS platform and version: Ubuntu 20.04.1
Screen resolution (i.e. 220dpi): I don't know

Steps to reproduce

Display a u at size 14.7

Expected behavior

u is good-looking

Actual behavior

u looks weird: the bottom right stem has sort of a glitch, where it overlaps to the inside part of the curve:

[ronjouch]

Here's another slightly bigger size looking funky:

[aaronbell]

Hi. What is interesting is that you can see on the 4 that it appears that the diagonal stroke is extending past the horizontal one. I'm guessing that you've installed the variable font version (since what you're observing happens where different strokes overlap). Did you install the OTF or TTF version?

However, I am not able to repro the issue that you're observing on Windows or Mac, which makes me suspect that it has something to do with how ubuntu is interpreting the font.

[ronjouch]

@aaronbell thanks for the fast feedback.

What is interesting is that you can see on the 4 that it appears that the diagonal stroke is extending past the horizontal one.

Indeed 👍.

I'm guessing that you've installed the variable font version (since what you're observing happens where different strokes overlap).

What do you mean by "the variable font version"?

Did you install the OTF or TTF version?

I had installed the TTF version. And, lo and behold, the OTF version doesn't exhibit the issue! Here's a screenshot of the OTF version at the same size as the initial screenshot (14.7), the problem is gone (but now descenders for y g j are cut, gah 😄, maybe this is my terminal's problem, though)

However, I am not able to repro the issue that you're observing on Windows or Mac, which makes me suspect that it has something to do with how ubuntu is interpreting the font.

Not just Ubuntu, though, I see the same thing on my Arch Linux machine (and I will confirm it's gone switching to OTF). So, maybe a bug in a common rendering library? Which one is responsible for this exactly? FreeType? Harfbuzz?

[aaronbell]

In the 2008.25 package, there are static OTFs (each weight is a separate .otf) and TTFs, both variable (all styles are contained within one .ttf file) and static (each weight is a separate .ttf).

When you installed the TTF version, did you install CascadiaCode.ttf or CascadiaCode-Regular.ttf?

[ronjouch]

In the 2008.25 package, there are static OTFs (each weight is a separate .otf) and TTFs, both variable (all styles are contained within one .ttf file) and static (each weight is a separate .ttf).

When you installed the TTF version, did you install CascadiaCode.ttf or CascadiaCode-Regular.ttf?

@aaronbell my initial report was with the variable TTF (all styles in one .ttf). After a rm -rf ~/.local/share/fonts/Saja* && fc-cache -fv followed by an install of static Cascadia_Code_Regular.ttf + Cascadia_Code_Bold.ttf, things look good (as good as when I installed OTF Regular+Bold, in my previous post):

→ Yes, the problem is specific to the variable TTF (all styles are contained within one .ttf file).

What could explain this?

[aaronbell]

It is probably an issue with FreeType's method of dealing with variable fonts, or fonts that have overlapping paths within one glyph (normally these overlaps are removed, but for variable fonts it is useful to preserve them).

Which version of FreeType are you running? According to the FreeType page you should be running 2.9 at minimum for proper Variable font support.

[ronjouch]

Which version of FreeType are you running? According to the FreeType page you should be running 2.9 at minimum for proper Variable font support.

@aaronbell I'm running the libfreetype6 2.10.1 package shipping as part of Ubuntu 20.04. Do you suggest I report this as a potential FreeType bug?

[aaronbell]

From what I can tell, that package doesn't look like it has the most up-to-date version of FreeType. Can you try upgrading to the latest? If the latest still shows the issue, then yeah, it should be reported.

[ronjouch]

From what I can tell, that package doesn't look like it has the most up-to-date version of FreeType. Can you try upgrading to the latest? If the latest still shows the issue, then yeah, it should be reported.

@aaronbell no and yes. No because in a non-rolling-release Linux (like Ubuntu), you never upgrade such a core package out of major versions, that's a recipe for a broken system. That being said, yes because my home machine runs Arch (which is a rolling release currently shipping the latest freetype 2.10.2) and exhibits the problem. Will file a bug upstream and closing this one. Thanks for all the guidance.

[ronjouch]

@aaronbell FYI, as I'm preparing the FreeType bug report:

• (Broken multi-font bundle) ftview -d 1024x768x24 30 CascadiaCode-2008.25/ttf/CascadiaCode.ttf
  
• (Good single font) ftview -d 1024x768x24 30 CascadiaCode-2008.25/ttf/static/CascadiaCode-Regular.ttf:
  
• A looping GIF animating between both:
  

[ronjouch]

Filed FreeType bug #59026: Multi-weight TTF of font "Cascadia Code" renders artifacts on some glyphs