touchscreen click events are not detected properly (on Linux)

[girtsf]

Describe the bug

With any widget, such as a Button or Label, .clicked() events are not recognized when the screen is tapped once. Instead, a single tap triggers long_touched() after a delay. Tapping twice in a quick succession generates a clicked() followed by a long_touched().

To Reproduce

Cargo.toml:

[package]
name = "repro"
version = "0.1.0"
edition = "2021"

[dependencies]
egui = { git = "https://github.com/emilk/egui", branch = "master" }
eframe = { git = "https://github.com/emilk/egui", branch = "master" }

src/main.rs:

#[derive(Default)]
struct App {
    log: String,
}

impl eframe::App for App {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        egui::CentralPanel::default().show(ctx, |ui| {
            let button = ui.button("click me");
            if button.clicked() {
                self.log.push_str("clicked()\n");
            }
            if button.long_touched() {
                self.log.push_str("long_touched()\n");
            }
            ui.label(&self.log);
        });
    }
}

fn main() {
    eframe::run_native(
        "test",
        eframe::NativeOptions::default(),
        Box::new(|_cc| Ok(Box::new(App::default()))),
    )
    .unwrap();
}

Steps to reproduce the behavior:

1. cargo run the above code
2. tap on "click me" button

Expected behavior
clicked() gets shown on the screen.

Screenshots

This can also be reproduced by egui_demo_app, built from latest master (d856f7b), by opening "Input Test" and tapping on "Sense::click" label:

Desktop:

• OS: Ubuntu 24.04
• Device: Lenovo Yoga 7 2-in-1 14IML9
• Wayland

(I tested on Windows, on a slightly different touchscreen-equipped Lenovo laptop, and it works correctly there.)

Additional context

This might be related to the observations found in #4668 ?

I bisected the behavior using egui_demo_app: last working commit is 8503a85, and it breaks at 8e5959d.

[Zoxc]

I see similar behavior on Android with 0.28.1.

[gfolkmanis-nhgh]

I did some further digging and found that we were not getting WindowEvent::Touch events from winit with TouchPhase::Ended when finger was lifted from the screen. Instead, the event would get sent together with the next TouchPhase::Started.

I confirmed the behavior happens with winit example code (no egui involved) on v0.30.2. Tested later versions and found that the issue was fixed in winit v0.30.4.

For funsies, I kept digging into winit changes, and it's likely that bumping to a newer smithay-client-toolkit fixed it (which brought in Smithay/client-toolkit@8708dd5). I didn't retest to confirm the exact root cause, but that's likely it.

So once egui switches to winit v0.30.4 or later, this issue should resolve itself. Looks like it is currently pinned to v0.30.2 as per #4849. Looks like the fix for that might be ready to go as of today, and #4939 might bring it in!