definite measure func

[ickshonpe]

Bevy version

Bevy Main doesn't support user measure funcs, so you need this branch:

bevy = { git = "https://github.com/ickshonpe/bevy.git", branch = "definite-measure-func" }

It just replaces the current measure func with this:

 let measure = taffy::node::MeasureFunc::Boxed(Box::new(
            move |_constraints: Size<Option<f32>>, available: Size<AvailableSpace>| {
                available.map(|a| a.into_option()).map(|v| v.unwrap_or(0.))
            },
        ));

and adds a resource bevy::ui::AlwaysUpdate which when present causes the UI to do a full update every frame.

What you did

https://github.com/ickshonpe/definite_measure_func

use bevy::prelude::*;
use bevy::ui::AlwaysUpdate;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup)
        .add_system(update)
        .run();
}

fn setup(mut commands: Commands) {
    commands.spawn(Camera2dBundle::default());
    commands.spawn((NodeBundle {
            background_color: Color::RED.into(),
            ..Default::default()
        },
        CalculatedSize::default()
    ));
}

fn update(
    mut commands: Commands, 
    input: Res<Input<KeyCode>>,
    always_update: Option<Res<AlwaysUpdate>>,
) {
    if input.just_pressed(KeyCode::Space) {
        if always_update.is_some() {
            commands.remove_resource::<AlwaysUpdate>();
        } else {
            commands.insert_resource(AlwaysUpdate);
        }
    }
}

What went wrong

unknown_2023.03.16-23.43_clip_1.mp4

The available horizontal space doesn't change when you enlarge the window horizontally.

Additional information

This can be fixed by doing a full update on all the nodes whenever the window resizes.
Because the full update gives the behaviour I expected, it looks to me like this is a bug and not just that I don't entirely understand the measure func constraints correctly or something.

It might just be that the only problem is that we weren't doing a full update on resizing when we needed to, but I'm not certain.

[nicoburns]

Definitely looks like a bug to me. Especially seeing as changing the vertical height fixes it! Weird that other layouts seem to work fine when resizing the window though...

[ickshonpe]

It's obvious now with this simple example, but I spent so many hours yesterday hacking around with the assumption there was something wrong with my text wrapping PR changes or the text pipeline 😅

[nicoburns]

@ickshonpe This should be fixed by Taffy v0.3.9

[ickshonpe]

Awesome, back to banging my head against the text-wrapping implementation 😣