Vanishing characters with TTF when using font size > 325 using Alloy / Poco

[FeralFox]

Build environment: Cloudpebble (Sorry I don't have much information here, probably Linux)

Description
I created a TTF font to draw shapes. This shape is an aperture consisting out of 8 segments. It works fine for font sizes < 324. However, when I change font size to 325, some segments start to vanish. When I increase the size further, more segments vanish, especially in the right lower section.
When I reduce the size to <324 and move the vanishing segments to the right, they are still shown.

The odd thing is, this does only happen if I draw single segments. When I draw the full picture (=All segments in a single TTF character), the full form is shown without any issues.

This behavior shown in the image below: The full shape is drawn in white as a single character. On top of that, using the same font size, there is each segment drawn in a different color. But some segments are not drawn, thus you can see the white "background" shape.

Steps to Reproduce
If it helps I can provide the code used to draw the image. I cannot attach the font here unfortunately, but I can upload it if it helps.

Expected behavior
All segments are drawn

[phoddie]

Thank you for the report.

Please provide an example project that reproduces this behavior. That's the only way to ensure that we have an unambiguous understanding of the issue being reported.

[FeralFox]

Sure, I have created a minimal example project to reproduce the error. I have exported it from Cloudpebble

There is a variable at the top of main.js where you can switch the font sizes between 320 (=working as expected) and 330 (=segments vanished)

examplevanishingttf.zip

[phoddie]

Thank you for the example. Very helpful.

Congratulations on creating a font with such huge glyphs that it overflows one of the internal glyph fields. Expanding that from 8 to 16 bits allow the 330 font to render correctly. I modified your example a bit for my testing, as you can see in this screen recording showing all segments.

segments.mov

[FeralFox]

It makes me very happy that you have found a solution!
Although I got an idea what the issue is, unfortunately I do not yet understand exactly what you did to solve it. Did you modify the TTF, or is it some modification which I can do in CloudPebble / Alloy to make this work?

Also, when allocating space is somehow the issue, would it be beneficial to expand the size of each glyph in the font, so that there is not so much "dead space"? (Would require more complicated calculation of the position of each segment)

But somehow it feels like a typical user-issue 😂

[phoddie]

It makes me very happy that you have found a solution!

Thank you! Me too. It was a little tricky to find. Fortunately, it was very easy to fix.

Apologies for not explaining more clearly.

You did nothing wrong. The font is valid. There is a bug in the font handling code in Alloy that caused a math overflow because of unexpected large values in the font.

The fix will be incorporated into a Pebble SDK update. Meanwhile, the only workaround is the one you discovered: use a smaller font.

[FeralFox]

Alright, sounds convenient!
Do you have an idea how long it usually takes for those updates to be incorporated and rolled out to CloudPebble?