Drop events on focus

[rezural]

This is a POC of dropping/suppressing of keyboard & mouse events, when the pointer is over any egui windows. Im not really that happy with it, but there is nothing wrong with it per-se, with the current state of bevy.

This is based off of jakobhellerman/bevy_egui#bevy-main, as it also depends on a slightly patched version of bevy:https://github.com/rezural/bevy/tree/input-derive-clone

I have gated it behind the drop_events_on_focus feature (feel free to rename this to something better), as while it is probably handy for bevy_egui consumers to opt into, it makes decisions about when to drop events, which are fairly arbitrary.

In reality, the application itself will probably want to decide which input state it is in (i.e. if there is a mouse pointer, or not), and a host of other concerns that will have to be fleshed out properly in bevy & the larger UI effort. I imagine this will come as a result of the bevy ui effort.

[rezural]

The actual only relevant commit is
53c1773

[rezural]

This shows an small example app that shows suppression of events, copy this into example/simple.rs, run with:

cargo run --example simple --features=drop_events_on_focus

use bevy::prelude::*;
use bevy_egui::{egui, EguiContext, EguiPlugin};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugin(EguiPlugin)
        .add_system(ui_example.system())
        .add_system(input_events.system())
        .run();
}

fn ui_example(egui_context: Res<EguiContext>) {
    egui::Window::new("Hello").show(egui_context.ctx(), |ui| {
        ui.label("world");
    });
    egui::Window::new("Hello2").show(egui_context.ctx(), |ui| {
        ui.label("world");
    });
}

fn input_events(mut ev_cursor: EventReader<CursorMoved>) {
    for event in ev_cursor.iter() {
        println!("Mouse move: {:?}", event);
    }
}

[rezural]

Fixes #47

[rezural]

One thing I only just thought of, is to leave most of the event consumption code the same in process_input system. And clear the input events in a system just after process_inputs.

If you think this PR has merit, I can rework this, so that most of process_input remains unchanged (except for the Input::clone())

[ndavd]

Any updates on this?