Timer example does not work correctly on current branch

[ogoffart]

Discussed in #3873

^{Originally posted by HitecExports November 7, 2023}
Hello!

Platform: Windows 11
Rust 1.73
slint = { git = "https://github.com/slint-ui/slint.git", branch = "master" }

Timer example does not work properly in current slint branch

"Elapsed Time" progress bar updates only while moving mouse in any area (even outside the main window)

So timer does not fire event automatically.

I noticed this problem for a week ago.

Before there were no such problem.

On Slint 1.2.2 same Timer Example works fine

Code (copied from Timer example)

// Copyright © SixtyFPS GmbH <info@slint.dev>
// SPDX-License-Identifier: MIT
use slint::{Timer, TimerMode};

slint::slint!(

    import { LineEdit, Button, Slider, HorizontalBox, VerticalBox } from "std-widgets.slint";

    export component MainWindow inherits Window {
        in-out property <duration> total-time: slider.value * 1s;
        in-out property <duration> elapsed-time;

        callback tick(duration);
        tick(passed-time) => {
            root.elapsed-time += passed-time;
            root.elapsed-time = min(root.elapsed-time, root.total-time);
        }

        VerticalBox {
            HorizontalBox {
                padding-left: 0;
                Text { text: "Elapsed Time:"; }
                Rectangle {
                    min-width: 200px;
                    max-height: 30px;
                    background: gray;
                    Rectangle {
                        x:0;
                        height: 100%;
                        width: parent.width * (root.elapsed-time/root.total-time);
                        background: lightblue;
                    }
                }
            }
            Text{
                text: (root.total-time / 1s) + "s";
            }
            HorizontalBox {
                padding-left: 0;
                Text {
                    text: "Duration:";
                    vertical-alignment: center;
                }
                slider := Slider {
                    maximum: 30s / 1s;
                    value: 10s / 1s;
                    changed(new-duration) => {
                        root.total-time = new-duration * 1s;
                        root.elapsed-time = min(root.elapsed-time, root.total-time);
                    }
                }
            }
            Button {
                text: "Reset";
                clicked => {
                    root.elapsed-time = 0
                }
            }
        }
    }
);

pub fn main() {
    let main_window = MainWindow::new().unwrap();
    let timer = Timer::default();
    {
        let main_window_weak = main_window.as_weak();
        timer.start(
            TimerMode::Repeated,
            std::time::Duration::from_millis(10),
            move || {
                let main_window = main_window_weak.unwrap();
                main_window.invoke_tick(10);
            },
        );
    }
    main_window.run().unwrap();
}

[ogoffart]

I've tried to debug to figure out what's wrong.

In the event loop, we get a AboutToWait event, and the next_timer is about to fire so the next_timer is very low value:

https://github.com/slint-ui/slint/blob/d82e3d4e5ce4e67a4d417ebcaf204680bf432072/internal/backends/winit/event_loop.rs#L571-573

We set control flow to ControlFlow with a wait duration of a a few, or 0ms. But we're never woken up.
Changing that to ControlFlow::Poll doesn't help.

[tronical]

I think winit uses SetTimer and the minimum resolution of that is around 16ms (USER_TIMER_MINIMUM). It might make sense for winit to use multimedia timers instead (timeSetEvent with a callback that wakes up winit), they offer a higher resolution. (That’s what Qt defaults to)

[ogoffart]

Filled rust-windowing/winit#3215