Smear-cursor starts using 100% cpu after continuous fast scrolling up and down

[dizzib]

Scrolling up and down continuously causes smear-cursor to start using 100% CPU, causing neovim to slow down to the point of becoming unresponsive.

This happens when smear-cursor is the only plug-in loaded.

Lazy config:

return {
  'sphamba/smear-cursor.nvim',
  event = 'VeryLazy',
  opts = {
    -- How fast the smear's head moves towards the target.
    -- 0: no movement, 1: instantaneous
    stiffness = 1,
  }
}

Environment

• OS: Alpine Linux running under Orbstack 2.0.4 on MacOS 15.5
• Terminal: ghostty 1.2.2
• Neovim version: 0.11.1
• Smear-cursor version/commit: abfa583

[sphamba]

Thank you for your report!

Unfortunately, I wasn't able to reproduce (using ghostty 1.2.3, neovim 0.11.1), scrolling through a 3MB image file and displaying many lines at once. But I remember experiencing this issue in the past...
If you have time and motivation, you could try to profile nvim execution to identify the culprit, for example using snacks.nvim profiler.

Alternatively, you can set the smear-cursor config delay_disable to disable it in a buffer when slow down is detected. See #132.

[dizzib]

Thank you for looking into this.

On further investigation, it seems this issue only manifests on files where scrolling is noticeably laggy, probably due to syntax highlighting, treesitter or lsp.

In my case, the filetype is typst which really seems to struggle with scrolling (I am looking at ways to optimise it).

It seems smear-cursor tips neovim over the edge, so to speak. I tried adding delay_disable = 500 but it did not help.

I am unable to reproduce this issue on other file types, such as txt, and smear-cursor works just fine.

My machine is a base Macbook Air M1.

[sphamba]

@dizzib Could you try the latest revision (on main)? I no longer force the animation loop to be called at regular intervals, so it should get stuck less.

[dizzib]

There does seem to be some improvement with commit a00f547 in that neovim slows down more gradually, but unfortunately it still grinds to an eventual halt if I keep scrolling as it is slowing down.

If I stop scrolling by removing my fingers off the trackpad, neovim may take anywhere from a few seconds to 1 or 2 minutes to recover and become responsive again.

I also notice the cursor doesn’t seem to jump around so much as before when scrolling vigorously.

With all my other plugins installed and smear-cursor removed neovim manages to keep running, albeit with a lot of lag, when continuously scrolling typst files.

[joesitton]

also experiencing this

[ToaLewa]

I was experiencing the same issue in a Typescript repository with tsserver running. The complete freeze was especially noticeable in combination with Project Launch (plugin that allows me to execute shell commands in a buffer). I normally launch my development web server in that buffer so I can search through the server logs. Trying to scroll through the logs (mainly with scroll wheel) would grind Neovim to a halt and sometimes freeze. I did not experiencing the lagging and freezing after disabling Smear. I'm running on a MacBook Pro with 36 GB memory and an Apple M4 Max chip.

I just downloaded the latest revision, and I will report back on performance.

[ToaLewa]

Still having the same issue with just 11 ts files open in buffers (with the number of files in this project it's not unreasonable for me to jump across 30). I think Smear recovers quicker now, but there's still a performance problem. I tested by scrolling through a 1.4 M log file. It even slows down just scrolling only with a few log files open.