Expose loading system fonts by Dimchikkk · Pull Request #14150 · bevyengine/bevy

Dimchikkk · 2024-07-05T10:45:50Z

Objective

Expose cosmic-text functionality to load system fonts.

Solution

Add load_system_fonts to TextPlugin struct.

Testing

cargo r --example text --release by setting load_system_fonts to true emoji is rendered correctly:

20240705113308386.mp4

Migration Guide

TextPlugin started to have a field, so in places where TextPlugin was used have to use bevy_text::TextPlugin::default() or create a struct with load_system_fonts field.

examples/ui/text.rs

crates/bevy_text/src/lib.rs

alice-i-cecile · 2024-07-14T17:05:04Z

crates/bevy_text/src/pipeline.rs

-        Self(cosmic_text::FontSystem::new_with_locale_and_db(locale, db))
+        let mut db = cosmic_text::fontdb::Database::new();
+        if load_system_fonts {
+            db.load_system_fonts();


I would really prefer if the loading strategy was more configurable: this should be easier to integrate into custom asset loading states for example.

alice-i-cecile

I think this is important to include, but the design and documentation needs more work. How do system fonts tie into Bevy's asset loading strategies? How can you look for a specific system font? How does font fallback function?

Dimchikkk · 2024-07-15T11:15:03Z

I think this is important to include, but the design and documentation needs more work. How do system fonts tie into Bevy's asset loading strategies? How can you look for a specific system font? How does font fallback function?

Thanks for the nice code review!

cosmic-text uses fontdb crate. fontdb crate has several methods to load fonts:

load single font from path, from bytes, etc
load fonts from dir
load all system fonts (basically the same as load fonts from dir but from specific dir where fonts are expected on platform)

fontdb has query function that allows to look for font, it returns None if font wasn't loaded.

cosmic-text has logic for handling font fallback - the algo seems pretty simple - if some glyph is missing it iterates over fallback fonts (that should be loaded prior) and tries to find the desired glyph. cosmic-text has custom font fallback implementation re-using some static fallback list from browsers: https://github.com/pop-os/cosmic-text/tree/main/src/font/fallback

So, my current PR just added a tiny bit for loading system fonts by calling load system fonts function from fontdb crate. The goal was to cover scenario when some glyph is missing cosmic-text will try to load from fallback list... just an example use case - emoji gonna work even without loading emoji font explicitly.

Querying specific fonts, setting font families, load from custom dirs need more design work but this small change is a small but quick win.

crates/bevy_text/src/lib.rs

examples/ui/text.rs

alice-i-cecile

Alright, I think I'm okay with this as an incremental next step. Some more suggestions on docs before we move forward though, to make it easier for others to modify and learn.

alice-i-cecile · 2024-07-15T21:04:36Z

crates/bevy_text/src/lib.rs

+    ///
+    /// For details on which directories are considered on each platform,
+    /// refer to the source code of [`fontdb::Database::load_system_fonts`](https://docs.rs/fontdb/latest/fontdb/struct.Database.html#method.load_system_fonts).
+    pub load_system_fonts: bool,


As a certain "Dimchikk" on Discord suggested, this would be more accurately described as "fallback to system fonts" :)

After giving it more thought and reading @TotalKrill's contemplations, I decided to extend the documentation for this member variable to mention its primary use case rather than renaming it.

janhohenheim · 2024-09-14T07:30:28Z

crates/bevy_text/src/lib.rs

 #[derive(Default)]
-pub struct TextPlugin;
+pub struct TextPlugin {
+    /// Attempts to load system fonts if [true].


Suggested change

/// Attempts to load system fonts if [true].

/// Attempts to load system fonts if `true`.

janhohenheim · 2024-09-14T07:32:52Z

crates/bevy_text/src/pipeline.rs

-        Self(cosmic_text::FontSystem::new_with_locale_and_db(locale, db))
+        let mut db = cosmic_text::fontdb::Database::new();
+        if load_system_fonts {
+            db.load_system_fonts();


I assume this just noops on Wasm and Android? Or what happens there? Do we get a warning?

janhohenheim · 2024-09-14T07:33:22Z

examples/ui/text.rs


 fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
+    // Emojis won't be rendered properly on wasm32 because the default loaded font doesn't support them, and loading system fonts isn't supported on this platform.
+    let text_content = if cfg!(target_arch = "wasm32") {


File system stuff usually doesn't work on Android either, FYI

janhohenheim · 2024-09-14T07:35:22Z

crates/bevy_text/src/pipeline.rs


+impl TextPipeline {
+    /// Create text pipeline providing a flag for loading system fonts
+    pub fn new(load_system_fonts: bool) -> Self {


TextPipeline::new(true) is very unreadable imo. Rename this to something like with_load_system_fonts.

janhohenheim · 2024-09-14T07:36:38Z

Looks mostly good, thanks. Just want to get clarification on some things and rename the fn new :)

alice-i-cecile · 2025-02-26T00:42:31Z

#16365 looks a bit more active; I'm going to close this out and try and consolidate work there. Your review on that would be appreciated

Dimchikkk and others added 3 commits July 5, 2024 11:29

expose loading system fonts

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clippy: derive Default trait

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clippy: fix typo

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DanielDK05 reviewed Jul 6, 2024

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alice-i-cecile added C-Feature A new feature, making something new possible A-Text Rendering and layout for characters S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Jul 7, 2024

alice-i-cecile added this to the 0.15 milestone Jul 7, 2024

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Dima added 2 commits July 15, 2024 12:23

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alice-i-cecile added S-Needs-Review Needs reviewer attention (from anyone!) to move forward and removed S-Waiting-on-Author The author needs to make changes or address concerns before this can be merged labels Jul 15, 2024

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bas-ie added S-Waiting-on-Author The author needs to make changes or address concerns before this can be merged and removed S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Sep 30, 2024

alice-i-cecile modified the milestones: 0.15, 0.16 Oct 8, 2024

TurtIeSocks mentioned this pull request Nov 17, 2024

Adds basic support for working with system fonts #16365

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alice-i-cecile closed this Feb 26, 2025

dsgallups mentioned this pull request Oct 5, 2025

Naive support for system fonts #21396

Closed

	/// Attempts to load system fonts if [true].
	/// Attempts to load system fonts if `true`.

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Dimchikkk commented Jul 5, 2024

Objective

Solution

Testing

Migration Guide

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Dimchikkk commented Jul 15, 2024 •

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