bevy_mouse_tracking_plugin

Tracking the mouse in bevy is kind of annoying. You gotta use Events, and EventReaders, and even then, they only get called when the mouse actually moves.

This crate aims to make this as easy as possible, by providing a static resource that tracks the mouse position every frame.

This crate also supports more complex use cases such as multiple cameras, which are discussed further down.

Basics

First, add the plugin to your app:

use bevy::prelude::*;
use bevy_mouse_tracking_plugin::MousePosPlugin;

App::new()
    .add_plugins(DefaultPlugins)
    .add_plugin(MousePosPlugin::SingleCamera);

Now, you can access the resource in your Systems:

use bevy_mouse_tracking_plugin::MousePos;
fn dbg_mouse(mouse: Res<MousePos>) {
    eprintln!("{}", *mouse);
}

...and don't forget to add the system to your app:

    .add_plugin(MousePosPlugin::SingleCamera)
    .add_system(dbg_mouse);

This will print the screen-space location of the mouse on every frame.

However, we can do better than just screen-space: we support automatic transformation to world-space coordinates via the [MousePosWorld] resource.

use bevy_mouse_tracking_plugin::MousePosWorld;
fn dbg_world(mouse: Res<MousePosWorld>) {
    eprintln!("{}", *mouse);
}

This will print the world-space location of the mouse on every frame.
Note that this is only supported for two-dimensional, orthographic camera, but pull requests for 3D support are welcome!

Multiple cameras

You may notice that if you try to use this plugin in an app that has multiple cameras, it crashes!

App::new()
    .add_plugins(DefaultPlugins)
    .add_plugin(MousePosPlugin::SingleCamera)
    .add_startup_system(setup)
    .run();

fn setup(mut commands: Commands) {
    commands.spawn_bundle(Camera2dBundle::default());
    commands.spawn_bundle(Camera3dBundle::default());
}

This panics with the following output:

thread 'main' panicked at 'cannot identify main camera -- consider adding the MainCamera component to one of the cameras', src\mouse_pos.rs:163:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This is because the plugin doesn't know which of the two cameras to use when figuring out the values of the MousePos and MousePosWorld resources. Let's take the panic message's advice.

    commands.spawn_bundle(Camera2dBundle::default())
        .insert(MainCamera); // added this line
    commands.spawn_bundle(Camera3dBundle::default());

Queries

If you want to get mouse tracking information relative to each camera individually, simply query for a MousePos or MousePosWorld as a component instead of as a resource.

App::new()
    // plugins omitted...
    .add_system(dbg_for_each);

fn dbg_for_each(mouse_pos: Query<&MousePosWorld>) {
    for pos in mouse_pos.iter() {
        // This prints the mouse position twice per frame:
        // once relative to the UI camera, and once relative to the physical camera.
        eprintln!("{}", *pos);
    }
}

If you want the mouse position for a specific camera, you can add query filters as always.
Note that as of bevy 0.6, the only way to tell the difference between a UI camera and an orthographic camera is by checking for the Frustum component.

use bevy::render::primitives::Frustum;
fn dbg_ui_pos(mouse_pos: Query<&MousePosWorld, Without<Frustum>>) {
    // query for the UI camera, which doesn't have a Frustum component.
    let pos = mouse_pos.single();
    eprintln!("{}", *pos);
}

No main camera

Let's say you have multiple cameras in your app, and you want to treat them all equally, without declaring any one of them as the main camera.
Change the plugin to this:

App::new()
    .add_plugins(DefaultPlugins)
    .add_plugin(MousePosPlugin::MultiCamera) // SingleCamera -> MultiCamera
    .add_startup_system(setup)
    // ...

Now, you can add as many cameras as you want, without having to worry about marking any of them as the main camera.
Note that MousePos and MousePosWorld will no longer be accessible as global resources -- you can only access them by Querying camera entities.

Mouse motion

This crate supports a resource that tracks mouse motion, via [MouseMotionPlugin]. The motion can be accessed from any system in a [MouseMotion] resource.

Crate name

As a final aside: the name of this crate is intentionally verbose. This is because I didn't want to steal a crate name, especially since it is very likely that this crate will eventually be made redundant by future updates to bevy.
I recommend renaming the crate in your Cargo.toml:

[dependencies]
mouse_tracking = { package = "bevy_mouse_tracking_plugin", version = "..." }

License: MIT