emilk/egui

High input latency with wgpu backend

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#5,037 opened on Aug 30, 2024

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bugegui-wgpuhelp wanted

Description

Describe the bug In the demo application, there is a delay in the application's response to input: windows move with a delay, elements react to the mouse over them with a delay, and button presses also have a delay. This issue is present in 0.28.1 and the master branch.

https://github.com/user-attachments/assets/87578e26-c0a6-4493-bbb9-37e5d863bbab

In my application, I also encountered this delay (Windows, Vulkan backend, egui-wgpu 0.28.1, and egui-winit 0.28.1). I found that the delay depends on the backend: it is lower on DX12 than on Vulkan.

I tested everything on release versions. The web version with egui.rs works fine.

At first, it seemed to me that I was doing something wrong in my application when I encountered this issue, but since it also occurs in the demo application, it seems the problem isn't related to something else; maybe it's with egui-wgpu.

Contributor guide

Tech stack
rust
Domain
performance
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Rustegui basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate the input latency issue in the egui wgpu backend. Start by profiling the event loop and rendering pipeline in the egui demo application, focusing on the wgpu backend. Compare behavior between Vulkan and DX12 backends to isolate the bottleneck. Look for any synchronization or buffer related delays in the wgpu integration code, possibly in files like `egui wgpu/src/renderer.rs` or `egui winit/src/state.rs`.