Surface lags behind on window resize

[nohenry]

Description
When resizing the window, the wpgu surface does not keep up with the size of the window. This is possibly a problem with winit instead.

Repro steps
Run any example in the wgpu/examples folder

Expected vs observed behavior
I expect the surface to resize exactly to the current window dimensions:

Screen.Recording.2023-05-07.at.1.11.19.PM.mov

But instead the surface lags behind the current window size:

Screen.Recording.2023-05-07.at.1.09.50.PM.mov

Platform
This is running on MacOS Ventura (Metal). Using wgpu on v0.16 git
I've not tested on Windows or Linux.

[nohenry]

Found the solution:

#[cfg(target_os = "macos")]
unsafe {
    surface
        .surface
        .as_hal_mut::<wgpu_hal::api::Metal, _, _>(|surface| {
            if let Some(surface) = surface {
                surface.present_with_transaction = true
            }
        });
}

[kpreid]

If it's that easy, perhaps this should be available as a safe operation. Reopen this issue?

[ifacodes]

If it's that easy, perhaps this should be available as a safe operation. Reopen this issue?

I agree, I feel like this issue has popped up a few times over the last few versions.

[nohenry]

One thing I want to know is if this a problem on different platforms (also how easy it would be to fix for them). I can test on Windows 11 and maybe Linux.

In terms of implementation, would it be best to have a field in the SurfaceConfiguration that determines this behaviour? I suppose it depends if this issue arises in the surface for other platforms.

[kpreid]

Another question is whether this should even be configurable, or just be the default. In other words: is there some situation where present_with_transaction should not be true? (For example, does it reduce performance when not resizing?)

[cwfitzgerald]

present_with_transaction afaik really limits the amount of frames in flight to under one, so unless you're making a UI app or other thing that needs to be resized all the time, it should be false so that the gpu can run independently.

One thing I want to know is if this a problem on different platforms (also how easy it would be to fix for them). I

@Ocrap7 there are issues on other platforms as resizing is an inherently racy problem. Afaik, DXGI can't do a truly smooth resize, though you can get close. Unfortunately the solutions will likely be different on each platform as each compositor is different.

[timtom-dev]

Any update on this? #3626 removed surface.as_hal_mut() so I've had to resort to this unholy abomination to get smooth resize on macOS:

#[allow(invalid_reference_casting)]
unsafe {
    surface.as_hal::<wgpu::hal::metal::Api, _, ()>(|surface| {
        if let Some(surface_ref) = surface {
            // AHH! Converting '&' to '&mut'
            let surface_mut = &mut *(surface_ref as *const wgpu::hal::metal::Surface as *mut wgpu::hal::metal::Surface);
            surface_mut.present_with_transaction = true;
        }
    });
}

which is obviously not ideal. 😬