Upgrading from 1.1.3 to 1.20 performance has degraded, with stutters

[AfflerZero]

Issue Description

When I am scrolling through the code in Neovim or typing in commands in the terminal like cat, the speed drops and causes a stutter or lag. This did not happen with the previous release build 1.1.3

I removed all traces of ghostty from my Macbook Pro and reinstalled with a clean state and no config setup, and the stuttering still remains.

Expected Behavior

When I am scrolling through code via neovim or cat a file, the text output or code navigation remains smooth with no stuttering.

Actual Behavior

With 1.20 release, I keep seeing UI stuttering or lagging when scrolling some code or inputting commands in the terminal.

Reproduction Steps

1. Open Ghostty
2. Cat a file or open code in vim
3. Scroll up or down with your arrow or jk keys
4. Observe the behavior

Ghostty Logs

Timestamp                       Thread     Type        Activity             PID    TTL  
2025-09-16 17:15:50.754337-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:15:50.884990-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:15:55.253713-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:15:55.253930-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: cmdline_url
2025-09-16 17:15:55.307840-0600 0x28b46f1  Error       0x0                  45291  0    ghostty: [com.mitchellh.ghostty:stream] unimplemented OSC callback: terminal.osc.Command{ .end_of_command = terminal.osc.Command__struct_18429{ .exit_code = 0 } }
2025-09-16 17:15:55.307900-0600 0x28b46f1  Error       0x0                  45291  0    ghostty: [com.mitchellh.ghostty:stream] unimplemented OSC command: end_of_command
2025-09-16 17:15:55.532187-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:15:55.923891-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:16:00.737584-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:16:00.737784-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: cmdline_url
2025-09-16 17:16:01.070317-0600 0x28b46f1  Error       0x0                  45291  0    ghostty: [com.mitchellh.ghostty:stream] ignoring CSI t with unimplemented parameter: ESC [  { 8, 34, 99 } t
2025-09-16 17:16:07.181394-0600 0x28b36fe  Debug       0x0                  45291  0    ghostty: [com.mitchellh.ghostty:AppDelegate] application will save window state
2025-09-16 17:16:10.252660-0600 0x28b46ed  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:font_codepoint_resolver] found codepoint 0x2714 in fallback face=Iosevka Curly
2025-09-16 17:17:00.807851-0600 0x28b46f1  Error       0x0                  45291  0    ghostty: [com.mitchellh.ghostty:stream] unimplemented OSC callback: terminal.osc.Command{ .end_of_command = terminal.osc.Command__struct_18429{ .exit_code = 0 } }
2025-09-16 17:17:00.807906-0600 0x28b46f1  Error       0x0                  45291  0    ghostty: [com.mitchellh.ghostty:stream] unimplemented OSC command: end_of_command
2025-09-16 17:17:01.057114-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:17:01.451872-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:17:04.818158-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:17:04.818334-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: cmdline_url
2025-09-16 17:17:04.843481-0600 0x28b46f1  Error       0x0                  45291  0    ghostty: [com.mitchellh.ghostty:stream] unimplemented OSC callback: terminal.osc.Command{ .end_of_command = terminal.osc.Command__struct_18429{ .exit_code = 0 } }
2025-09-16 17:17:04.843531-0600 0x28b46f1  Error       0x0                  45291  0    ghostty: [com.mitchellh.ghostty:stream] unimplemented OSC command: end_of_command
2025-09-16 17:17:05.069452-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key
2025-09-16 17:17:05.456713-0600 0x28b46f1  Info        0x0                  45291  0    ghostty: [com.mitchellh.ghostty:osc] unknown semantic prompts option: special_key

Ghostty Version

Ghostty 1.2.0

Version
  - version: 1.2.0
  - channel: stable
Build Config
  - Zig version   : 0.14.1
  - build mode    : builtin.OptimizeMode.ReleaseFast
  - app runtime   : apprt.Runtime.none
  - font engine   : font.main.Backend.coretext
  - renderer      : renderer.generic.Renderer(renderer.Metal)
  - libxev        : kqueue

OS Version Information

Macbook Pro year 2019 - OS Sequoia 15.6.1

(Linux only) Display Server

None

(Linux only) Desktop Environment/Window Manager

No response

Minimal Ghostty Configuration

None

Additional Relevant Configuration

No response

I acknowledge that:

• I have reviewed the FAQ and confirm that my issue is NOT among them.
• I have searched the Ghostty repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.

[AfflerZero]

I have a tracelog if you need that.
Uploading LaggyWhenScolling.trace.zip…

[mitchellh]

Can you screenshot some of the heavy parts of the trace for me?

[AfflerZero]

Here is a screenshot from Activity Monitor

[AfflerZero]

I will keep looking into it and hopefully find a reason why it's not working. It might be my setup, but I will download the debug ghostty and learn to debug an app instead of network calls

[mitchellh]

You're the first person to report anything like this so that's surprising. All our benchmarks that we run across IO, frame times, and framerates only improved with 1.2 from 1.1.x. Our renderer is significantly more performant on everything we've thrown at it that we can measure. And like I said, nobody has said or shown otherwise.

So, if you can share some more details that'd be great. The trace is helpful but it'll take me some time to get to it.

[AfflerZero]

I was surprised too, that's removed my config to see if that was the issue, plus reinstalled to see if there was a corrupt setting somewhere.

I don't know if it's because I am still running an intel MacBook Pro. I am planning to upgrade this winter, but I am curious why it's happening. I will do some investigation, but I don't know much about Zig.

[AfflerZero]

I think I finally nailed down the root cause, I was messing with shaders, as this was part of the new release. The shaders don't work for me, even if I use the demo one that is listed in the Ghostty release notes for 1.2.0.

Yesterday I was editing in two different areas like textmate and Neovim which was causing swap file issues. Even though I reinstalled ghostty the swap file issue is still there, so l cleaned in up, and it seems to be better.

The shaders are still not working, this is what I added to the config

custom-shader = shaders/blazer.glsl

Even after commenting out the shaders, the performance isn't where it was before the shaders were added.

Here is the video
DemoWithShaders.mov.zip

[mitchellh]

I don't have any way to access Intel hardware anymore, so I'm not going to be able to debug this. If you can find a way to debug this yourself, please do so. Otherwise, we may have to consider dropping Intel support because we simply can't support this platform in any reasonable way anymore. Consider downgrading to 1.1.3, sorry.

[AfflerZero]

No worries, if I have time I can investigate what the problem is but at the same time intel MacBooks are being phased out, not sure if the fix will be worth it.

I will try to see if I can fix it or not and do a patch fix, if possible.

Thanks for your time

[mitchellh]

I appreciate it thank you