Input lag on HiDPI 4K when maximizing window

[clamydo]

What Operating System(s) are you seeing this problem on?

Windows

Which Wayland compositor or X11 Window manager(s) are you using?

Windows 10

WezTerm version

20230712-072601-f4abf8fd

Did you try the latest nightly build to see if the issue is better (or worse!) than your current version?

No, and I'll explain why below

Describe the bug

I experience a noticeable input lag (up to estimated 500 ms) proportional to the size of the window and of the screen resolution (when I move a window between displays of different resolutions). This is true for both WebGPU and OpenGL mode. The performance on Dx12 is much better than with Vulkan backend.

However, it feels to me, in fullscreen (without decorator) the lag is smaller again even on 4K resolution.

I am on a Intel(R) Core(TM) i7-8565U CPU with integrated Intel GPU. Is it too weak?

I tried the current nightly (20230712-072601-f4abf8fd), but it crashed when resizing the window.

On my, admittedly substantially beefier, Linux machine I have no issues.

To Reproduce

Open a new window, type, observe lag between pressing key and appearance of the character on the screen.

Configuration

config.front_end = "WebGpu"
config.webgpu_power_preference = "HighPerformance"
config.webgpu_preferred_adapter = {
	backend = "Dx12",
	device = 16032,
	device_type = "IntegratedGpu",
	name = "Intel(R) UHD Graphics 620",
	vendor = 32902,
}

Expected Behavior

No (noticable) input lag, even on slightly dated laptop hardware.

Logs

Debug Overlay
wezterm version: 20230712-072601-f4abf8fd x86_64-pc-windows-msvc
Window Environment: Windows
WebGPU: name=Intel(R) UHD Graphics 620, device_type=IntegratedGpu, backend=Dx12, vendor=32902, device=16032
Enter lua statements or expressions and hit Enter.
Press ESC or CTRL-D to exit

Anything else?

Thx for making Wezterm. I ❤️ it!

[wez]

FWIW, the resize crash is from the upstream wgpu crate:

• Resize error on DX12 backend in wgpu 0.17 gfx-rs/wgpu#3967

[wez]

Can you clarify what you mean by 500ms of input lag? Are you saying that every key press takes 500ms to render?
Only in certain applications? Is it that bad in the debug overlay itself?

[clamydo]

Are you saying that every key press takes 500ms to render?

Exactly. The time between key press and rendering.

Update: I've tried to measure it with the slomo mode of my camera, which puts it more in the 200+-50 ms ballpark for maximised window and 100 ms for full screen.

Only in certain applications? Is it that bad in the debug overlay itself?

Independent of applications and shells (in WSL2!) and also in the debug overlay.

[MartenBE]

I am also having this issue on Fedora 41 KDE with wezterm 20241104_083404_51c794ac. Maximizing the window on 4K screen really increases the CPU usage used by wezterm and it becomes slow to respond. Resize it to a smaller window and cpu usage and lag also scale down.