Issues with set_cursor_grab(true)

[vdrn]

Trying out set_cursor_grab on X11 (Ubuntu 20.04) I've encountered a couple of issues:

1. mouse_position() coordinates are wrong:
   • they are not changing by appropriate amount as the mouse moves
   • they keep on changing even when the mouse is stuck (ie: if you keep dragging mouse into top-left corner, they will keep on decreasing to negative values)
2. Alt-tabbing to another window, so the macroquad window is no longer focused, will keep the mouse locked to macroquad's window.

How to reproduce: Add set_cursor_grab(true); to ui.rs example. This will make all ui elements not clickable by mouse.

[GRASBOCK]

Can reproduce. One can still click the UI elements, but not where one would expect them to be. Like you said the mouse position has the wrong values.

[GRASBOCK]

I tried to figure this out.

In miniquad it works just fine. Meaning it is not an issue with x11, because there is no platform specifics in macroquad as far as I know. Here an example

use miniquad::*;

struct Stage {}
impl EventHandler for Stage {
    fn update(&mut self, _ctx: &mut Context) {}

    fn raw_mouse_motion(&mut self, ctx: &mut Context, dx: f32, dy: f32) {
        println!("relative mouse motion: {dx}, {dy}");
    }

    fn mouse_motion_event(&mut self, ctx: &mut Context, x: f32, y: f32){
        println!("absolute mouse position: {x}, {y}");
    }

    fn draw(&mut self, ctx: &mut Context) {
        ctx.clear(Some((0., 1., 0., 1.)), None, None);
    }
}

fn main() {
    miniquad::start(
        conf::Conf {
            window_title: "Miniquad".to_string(),
            window_width: 100,
            window_height: 100,
            ..Default::default()
        },
        |_ctx| {
            _ctx.set_cursor_grab(true); // <--- constraining the cursor
            Box::new(Stage {})
        }
    );
}

Looking at the definition of set_cursor_grab() I can see that someone has already considered the second problem.

/// Capture mouse cursor to the current window
/// On WASM this will automatically hide cursor
/// On desktop this will bound cursor to windows border
/// NOTICE: on desktop cursor will not be automatically released after window lost focus
///         so set_cursor_grab(false) on window's focus lost is recommended.
/// TODO: implement window focus events
pub fn set_cursor_grab(&mut self, grab: bool) {
...

So that requires window focus events being implemented.

So the problem lies somewhere in macroquad. Inside the mouse_motion_event() callback function one can see, that the mouse position is only updated in absolute values if the cursor is not grabbed.

fn mouse_motion_event(&mut self, _: &mut miniquad::Context, x: f32, y: f32) {
    let context = get_context();
    // context.mouse_position = Vec2::new(x, y); // adding this line fixes the problem
    if !context.cursor_grabbed {
        context.mouse_position = Vec2::new(x, y);

The relative motion is however only used if it is grabbed.

fn raw_mouse_motion(&mut self, _: &mut miniquad::Context, x: f32, y: f32) {
    let context = get_context();
    if context.cursor_grabbed {
        context.mouse_position += Vec2::new(x, y);

cursor_grabbed is used at a lot of places like on mouse down where I didn't expect it to be used. Could it be, that someone misunderstood cursor_grabbed for "mouse is being held down"? I am confused as to why the context.mouse_position is not set independent of cursor_grabbed.

[siddharthroy12]

This was added along with the support for capture mouse in this commit 5c8a93529ee82688c99471f206ce9d8b719b2f2a by @Pebaz but I have no idea why he added these cursor_grabbed check there

[siddharthroy12]

In raylib when cursor is grabbed it also hide it and to un-grab the cursor when window is un-focused miniquad needs to add this feature to check if window is focused or not

[siddharthroy12]

Related to https://github.com/not-fl3/miniquad/pull/27 https://github.com/not-fl3/miniquad/issues/28

[CoherentThought]

This issue still appears in version 0.4.13 of macroquad on linux at least.