Font rendering broken

[Kirottu]

Font rendering seems completely broken on the latest release, there is no transform applied to this text but it still comes out like this:

It is supposed to say "RECTANGLE".

[jrmuizel]

What OS are you on?

[Kirottu]

I use linux, and wayland if that is relevant.

[J-Cake]

IFAIK Raqote generally delegates text rendering to the developer. I've encountered this a few times. Here's the approach I used

[FoundationKen]

Would it be fairly easy to integrate cosmic-text with raqote to get better text support?

https://github.com/pop-os/cosmic-text

[FoundationKen]

At least as a proof-of-concept, my colleague got it working in a few minutes:

https://github.com/Foundation-Devices/raqote-cosmic-text/blob/main/src/main.rs

[andreubotella]

I was playing around with raqote on linux, and I noticed this issue on the various fonts I tried. And when I dug deeper, I found that it seems like that the advance width for the glyphs in draw_text has the wrong scaling factor.

Per the font-kit documentation, font.advance(id) returns a distance in font units, and this TrueType documentation says that the scaling factor to turn font units into pixels is point_size * resolution / (72 * units_per_em). units_per_em is a font-specific value, which you can get from font-kit with font.metrics().units_per_em. The display resolution isn't available to raqote, but at least one piece of code in font-kit always uses 72 dpi. Fixing this results in text that does appear properly rendered.

No part of this scaling factor is platform-specific, or specific to the underlying font technology (i.e. FreeType vs Core Text), so I wonder why this comment implies that it does work on some platforms. If it's related to the screen resolution, I wonder why font-kit hardcodes 72 dpi. Otherwise, I can only conclude that if the current scaling factor really does work on some platforms, then font-kit might be buggy in those platforms.

[J-Cake]

I was playing around with raqote on linux, and I noticed this issue on the various fonts I tried. And when I dug deeper, I found that it seems like that the advance width for the glyphs in draw_text has the wrong scaling factor.

Per the font-kit documentation, font.advance(id) returns a distance in font units, and this TrueType documentation says that the scaling factor to turn font units into pixels is point_size * resolution / (72 * units_per_em). units_per_em is a font-specific value, which you can get from font-kit with font.metrics().units_per_em. The display resolution isn't available to raqote, but at least one piece of code in font-kit always uses 72 dpi. Fixing this results in text that does appear properly rendered.

No part of this scaling factor is platform-specific, or specific to the underlying font technology (i.e. FreeType vs Core Text), so I wonder why this comment implies that it does work on some platforms. If it's related to the screen resolution, I wonder why font-kit hardcodes 72 dpi. Otherwise, I can only conclude that if the current scaling factor really does work on some platforms, then font-kit might be buggy in those platforms.

To reiterate, draw_text is not meant to be used. It's meant to do the bare minimum