Shader using Time causes high CPU usage and laggy input, after running hours.

[donaldwuid]

Windows Terminal version

1.24.10921.0

Windows build number

No response

Other Software

No response

Steps to reproduce

1. download https://github.com/Hammster/windows-terminal-shaders
2. enable shaders with Time used, e.g., hueshift.hlsl, crt.hlsl(with GRAIN or REFRESHLINE on)
   (how to enable shaders: https://github.com/microsoft/terminal/blob/main/samples/PixelShaders/README.md
3. run a new Windows Terminal window, ensure the shader is applied.
4. [BUG REPRODUCED!!!] keep this window running, after hours or one day, this windows consumes lots of CPU and input is very laggy
5. and then, while this window still running, disable the shader by deleting pixelShaderPath in the json config, bug is gone, CPU and input recovers

Expected Behavior

regular cpu usage and smooth input

Actual Behavior

huge cpu usage and laggy input

[Zish19]

I'd like to investigate this. It sounds like a float accumulation or time delta issue. Could you please assign it to me?

[carlos-zamora]

Thanks for filing! Yeah, this sounds like an issue with how we're handling pixel shaders, for sure. Question for you: what's the difference between CPU and GPU usage after like an hour /? That may help us track this down better. What kind of graphics driver are you using?

@Zish19 we don't generally assign issues out to community members, but definitely go ahead. Any help here would be appreciated 😊.

[Zish19]

I’ll try this locally with the sample shaders using Time (hueshift.hlsl, crt.hlsl) and monitor CPU/GPU usage over longer runtimes.

My current suspicion is either excessive invalidation/repaint in the render loop over time, or a precision/accumulation issue related to the shader time uniform after long uptime.
I’ll also check whether this is driver/API specific and whether the CPU usage is coming from the renderer thread or shader constant updates.

[donaldwuid]

note, when this bug happens, the framerate of the window is OK, i.e. the animation is smooth.
Only the CPU and input is laggy.