Bevy Debug Text Overlay

A proof of concept for adding a very convenient text overlay macro to the bevy game engine.

This is derived from the code I used during the first bevy game jam. There are major improvements: most notably the text doesn't jump around all the time, and each message can have its own color.

screen_print! is very convenient, if you are an incorrigible println-debugger, you will love this crate when working with bevy!

Usage

[dependencies]
bevy-debug-text-overlay = "8.1.0"

This bevy plugin is fairly trivial to use. You must:

1. Add the OverlayPlugin to your app
2. Use the screen_print! macro wherever you want, just use it like you would use println!, no need to pass special arguments.

This will display on the top left of the screen the text for a short time.

Please see the screen_print! documentation for detailed usage instructions.

Code example

use bevy::prelude::*;
use bevy_debug_text_overlay::{screen_print, OverlayPlugin};

fn main() {
    App::new()
        // !!!!IMPORTANT!!!! Add the OverlayPlugin here
        .add_plugins((DefaultPlugins, OverlayPlugin { font_size: 23.0, ..default() }))
        .add_systems(Startup, setup)
        .add_systems(Update, screen_print_text)
        .run();
}
fn setup(mut commands: Commands) {
    commands.spawn(Camera2dBundle::default());
}
// Notice how we didn't have to add any special system parameters
fn screen_print_text(time: Res<Time>) {
    let current_time = time.elapsed_seconds_f64();
    let at_interval = |t: f64| current_time % t < time.delta_seconds_f64();
    let x = (13, 3.4, vec![1,2,3,4,5,6,7,8]);
    if at_interval(0.1) {
        let last_fps = 1.0 / time.delta_seconds();
        screen_print!(col: Color::CYAN, "fps: {last_fps:.0}");
        screen_print!("current time: {current_time:.2}")
    }
    if at_interval(2.0) {
        let col = Color::FUCHSIA;
        screen_print!(sec: 0.5, col: col, "every two seconds: {}, {:?}", x.0, x.2)
    }
    if at_interval(5.0) {
        screen_print!(sec: 3.0, "every five seconds: {x:#?}");
    }
}

This should look like as follow:

2022-03-16.08-23-27.mp4

Cargo features

debug

It is possible to replace screen_print! by an empty macro by disabling the debug cargo feature. This also disables all of bevy-debug-text-overlay dependencies, since there is no code to run.

No further action is required to completely disable the plugin. Mock implementations are provided for release mod.

To use that feature, you can setup your Cargo.toml as follow:

# Add a debug feature to your own Cargo.toml, make it default
[features]
debug = ["bevy-debug-text-overlay/debug"]
default = ["debug"]

# Manually specify features for bevy-debug-text-overlay (omitting "debug")
bevy-debug-text-overlay = { version = "8.1.0", default-features = false }

Now when making your release build, you should use

cargo build --release --no-default-features

I'm aware that it can be cumbersome for some, please fill an issue if this really doesn't mix well with your own workflow.

Known limitations

I'm welcoming contributions if you have any fixes:

• There is no way to specify the overlay position with regard to user-defined UI, so you might end up with the debug text showing behind your own UI.
• There is a very custom, very dodgy resource allocation module. If someone can link me to a good 1D res alloc crate, I'd be happy to use it instead of block.
• This is not part of bevy itself, so you gotta add it as a dependency to your app :(
• You can't set it up so that it's displayed from the bottom up or to the right of the screen.

Changelog

• 2.0.0: Breaking: bump bevy version to 0.7 (you should be able to upgrade from 1.0.0 without changing your code)
• 3.0.0: Breaking: bump bevy version to 0.8 (you should be able to upgrade from 2.0.0 without changing your code)
• 4.0.0: Breaking: bump bevy version to 0.9 (you should be able to upgrade from 3.0.0 without changing your code)
• 4.0.1: Fix the README "Usage" version
• 5.0.0: Breaking: bump bevy version to 0.10 (you should be able to upgrade from 4.0.1 without changing your code)
• 5.1.0: Add the push option to screen_print! macro, this allows printing multiple messages from the same macro call, this makes the macro usable in loops, or for messages that makes sense to duplicate on screen.
• 6.0.0: Breaking: bump bevy version to 0.11
  • Remove the font field from Options and OverlayPlugin, we now use the bevy default font. Set it yourself if you want to use something else than the default font.
• 7.0.0: Breaking: bump bevy version to 0.12
• 8.0.0: Breaking: bump bevy version to 0.13, remove builtin-font feature.
• 8.1.0:
  • Use $crate:: inside the screen_print! macro, so that it can be invoked with the crate path
  • Do not panic on exceeding 4096 prints per frame, instead log an error
  • Use the std OnceLock over lazy_static!

Version matrix

bevy	latest supporting version
0.13	8.1.0
0.12	7.0.0
0.11	6.0.0
0.10	5.1.0
0.9	4.0.1
0.8	3.0.0
0.7	2.0.0
0.6	1.0.0

API stability warning

This is a tinny crate so it's literally impossible to cause major breaking changes. But I'm not convinced the current macro API is optimal, and it might change in the future.

License

This library is licensed under Apache 2.0.