Nested text spans are not rendered if the `default_font` feature is disabled

[rparrett]

Bevy version

0.15.0-rc.3, also current main

Relevant system information

SystemInfo { os: "MacOS 14.5 ", kernel: "23.5.0", cpu: "Apple M1 Max", core_count: "10", memory: "64.0 GiB" }
AdapterInfo { name: "Apple M1 Max", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }

What you did

• Disable default-features
• Decline to enable default_font feature
• Use nested text spans where the (empty) root node uses TextFont::default() either by omission of the component, or by explicitly setting it to that value.

https://github.com/rparrett/bevy-default-font-bug

git clone https://github.com/rparrett/bevy-default-font-bug
cd bevy-default-font-bug
cargo run

What went wrong

No text is displayed

Additional Information

Relevant snippet pasted here for convenience

let font = asset_server.load("FiraSans-Bold.ttf");
commands
    .spawn((
        Text::default(),
        // Uncommenting this makes things work
        // TextFont {
        //     font: font.clone(),
        //     ..default()
        // },
    ))
    .with_children(|parent| {
        parent.spawn((
            TextSpan::new("span, should be visible"),
            TextFont { font, ..default() },
        ));
    });

[rparrett]

(Probably the same bug) can be reproduced in-repo by replacing the default font with an invalid font handle instead.

Expand code

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .run();
}

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn(Camera2d);

    commands.spawn(Text::new("no default font, expected to not be visible"));

    commands
        .spawn((
            Text::default(),
            TextFont {
                // Commenting the next line makes things work
                font: asset_server.load("fonts/dne.ttf"),
                font_size: 25.0,
                ..default()
            },
        ))
        .with_children(|parent| {
            parent.spawn((
                TextSpan::new("span, should be visible"),
                TextFont {
                    font_size: 25.0,
                    ..default()
                },
            ));
        });
}

[rparrett]

This could be rephrased like "if any text span has an invalid font handle, the entire text does not render."

[UkoeHB]

TextPipeline::update_buffer exits early if any font is not available. It will wait until all fonts are loaded.

[cart]

Investigating our options now

[cart]

I think the biggest issue to resolve for 0.15 is "spans with valid fonts nested under empty Text not rendering by default if there is no default font".

A fix that feels reasonable for that would be to skip empty spans / not fail out for "not yet loaded" fonts when text is empty. I'll give that a try.

The long term (likely harder) and more controversial fix would be to more effectively iteratively render text as fonts load. However this would result in unnecessary re-layouts + pop in. Idk if thats desirable.