Sequence of mouse movements seems out of order when using trackpad on macOS

[dmbfm]

I'm developing a drawing application and I noticed a weird artifact with mouse positions when drawing with a trackpad on macOS (I'm using a macbook M1 pro on macOS 14.3.1, and using winit 0.29.10).

What I do is each frame I collect all of the incoming positions CursorMoved window event and store them in a vec. Then when it comes to draw the frame I connect these points with lines.

When using a mouse everything works fine, but when using a trackpad I noticed that I got a lot of weird loops and spikes coming out of the drawn lines. For instance:

In the image above different colors refer to different frames. Notice that the blue line does a sort of 'V' shape, so it appears the mouse locations are coming in out of order.

By commenting out this line,

winit/src/platform_impl/macos/view.rs

Line 738 in a127bd6

self.mouse_motion(event);

which then blocks the pressureChange event from emitting CursorMoved events, this artifacts go away and everything works correctly.

It seems like the position from pressureChange is not equivalent from regular mouse positions, or maybe macOS does not process them in the same order, causing these loops to appear.

[madsmtm]

Huh, in general, I find it odd the amount of places we're calling mouse_motion; I'd imagine they only really need calling inside mouseMoved:, mouseDragged:, rightMouseDragged: and otherMouseDragged:, it should be redundant everywhere else.

Will need to do some digging in the project history to see why it is like it is.

[madsmtm]

This was added in #1490, but I can't seem to reproduce the original issue, it's possible that issue has been fixed in macOS itself in the meantime, and the workaround is unnecessary in newer versions?

[madsmtm]

I tried debug-logging the data in the event sent to pressureChangeWithEvent:, but from my findings, it appears to be executed after mouseMoved:, and always with the same data as mouseMoved:. So while perhaps a bit inefficient, because we emit the same event twice, it doesn't seem like it should cause the issues you're seeing?

Can you provide a minimal example where you can reproduce the jittery behaviour? Maybe by trying one of the examples in this repo (likely window), click-drag your mouse across the window, and see if the output is jittery?

[dmbfm]

I had a hard time identifying the jitter via the window example, but this not-so-minimal project reproduces the issue on my machine: https://github.com/dmbfm/winit-macos-mouse-movement

Here is an example:

I just updated to macOS 14.4 and the issue still happens. Maybe it is specific to the macbook M1 pro because of the 120hz refresh rate or something like that?

[madsmtm]

Thanks for the example, I could reproduce the problem (even with a refresh rate of 60Hz, so I don't think that's it).

I've opened #3601 to fix this in the manner you suggested to begin with.