3b80f72dac
This PR partially addresses #4504 with a one-liner, all feedback is very welcome. ### AI disclaimer I used Claude Code to help navigate the various layers of the rendering stack, to instrument a ton of intermediate now-deleted log statements, and ultimately to identify and fix this bug. I directed it conversationally, gave it experiments to run, audited all of its work, threw most of it out, and finally landed on this extremely small and simple change that fixes the issue _for me_ but I think for a lot of other cases as well. The fix ended up being small, so hopefully it's easy to review and discuss. Details: # Fix horizontal glyph spacing on non-Retina displays On external monitors (1.0x scale, 72 DPI), text had excessive horizontal spacing between glyphs. The issue was less noticeable on Retina displays (2.0x scale, 144 DPI) due to higher pixel density, but the proportional spacing error was identical. ## Before Background is ghostty 1.2.3 from homebrew, foregreound is iTerm2: <img width="862" height="938" alt="Screenshot 2025-10-31 at 3 04 47 PM" src="https://github.com/user-attachments/assets/feff5279-05cc-4008-b2f5-8ea3b4d6d14b" /> ## After Background is ghostty tip + this change, foreground is iTerm2: <img width="659" height="774" alt="Screenshot 2025-10-31 at 3 00 42 PM" src="https://github.com/user-attachments/assets/702dc7f8-bb46-43ec-8156-f69d003e8a37" /> (my iTerm2 has some custom thickening / brightening you can see; that's not a part of this change) ## Root Cause The metrics calculation in Metrics.zig used `@ceil()` to round the cell width from CoreText's glyph measurements, which created a mismatch between cell width (which determines glyph positions) and the actual glyph advances. At 72 DPI with a 12pt font: - CoreText returns glyph advance: 7.224609375 pixels - Cell width was ceiled to: 8 pixels - Gap per character: 0.78 pixels (~10.8% error) At 144 DPI with the same font: - CoreText returns glyph advance: 14.44921875 pixels (exactly 2x) - Cell width was ceiled to: 15 pixels - Gap per character: 0.55 pixels (~3.8% error) The error at high DPI is much better than at low DPI, since the absolute error is always no more than 1px. ## Fix Changed `@ceil(face_width)` to `@round(face_width)`. This makes cell width match the glyph advances better, reducing the error to at most 0.5px: - 72 DPI: round(7.22) = 7 - 144 DPI: round(14.45) = 14 Height continues using `@ceil()` since vertical space can be slightly larger without visual issues, but... should it? I'm not sure; this is a good topic for discussion.
Ghostty
Fast, native, feature-rich terminal emulator pushing modern features.
About
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Documentation
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Contributing
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Developing
About
Ghostty is a terminal emulator that differentiates itself by being fast, feature-rich, and native. While there are many excellent terminal emulators available, they all force you to choose between speed, features, or native UIs. Ghostty provides all three.
In all categories, I am not trying to claim that Ghostty is the best (i.e. the fastest, most feature-rich, or most native). But Ghostty is competitive in all three categories and Ghostty doesn't make you choose between them.
Ghostty also intends to push the boundaries of what is possible with a terminal emulator by exposing modern, opt-in features that enable CLI tool developers to build more feature rich, interactive applications.
While aiming for this ambitious goal, our first step is to make Ghostty one of the best fully standards compliant terminal emulator, remaining compatible with all existing shells and software while supporting all of the latest terminal innovations in the ecosystem. You can use Ghostty as a drop-in replacement for your existing terminal emulator.
For more details, see About Ghostty.
Download
See the download page on the Ghostty website.
Documentation
See the documentation on the Ghostty website.
Contributing and Developing
If you have any ideas, issues, etc. regarding Ghostty, or would like to contribute to Ghostty through pull requests, please check out our "Contributing to Ghostty" document. Those who would like to get involved with Ghostty's development as well should also read the "Developing Ghostty" document for more technical details.
Roadmap and Status
The high-level ambitious plan for the project, in order:
| # | Step | Status |
|---|---|---|
| 1 | Standards-compliant terminal emulation | ✅ |
| 2 | Competitive performance | ✅ |
| 3 | Basic customizability -- fonts, bg colors, etc. | ✅ |
| 4 | Richer windowing features -- multi-window, tabbing, panes | ✅ |
| 5 | Native Platform Experiences (i.e. Mac Preference Panel) | ⚠️ |
| 6 | Cross-platform libghostty for Embeddable Terminals |
⚠️ |
| 7 | Windows Terminals (including PowerShell, Cmd, WSL) | ❌ |
| N | Fancy features (to be expanded upon later) | ❌ |
Additional details for each step in the big roadmap below:
Standards-Compliant Terminal Emulation
Ghostty implements enough control sequences to be used by hundreds of testers daily for over the past year. Further, we've done a comprehensive xterm audit comparing Ghostty's behavior to xterm and building a set of conformance test cases.
We believe Ghostty is one of the most compliant terminal emulators available.
Terminal behavior is partially a de jure standard (i.e. ECMA-48) but mostly a de facto standard as defined by popular terminal emulators worldwide. Ghostty takes the approach that our behavior is defined by (1) standards, if available, (2) xterm, if the feature exists, (3) other popular terminals, in that order. This defines what the Ghostty project views as a "standard."
Competitive Performance
We need better benchmarks to continuously verify this, but Ghostty is generally in the same performance category as the other highest performing terminal emulators.
For rendering, we have a multi-renderer architecture that uses OpenGL on Linux and Metal on macOS. As far as I'm aware, we're the only terminal emulator other than iTerm that uses Metal directly. And we're the only terminal emulator that has a Metal renderer that supports ligatures (iTerm uses a CPU renderer if ligatures are enabled). We can maintain around 60fps under heavy load and much more generally -- though the terminal is usually rendering much lower due to little screen changes.
For IO, we have a dedicated IO thread that maintains very little jitter
under heavy IO load (i.e. cat <big file>.txt). On benchmarks for IO,
we're usually within a small margin of other fast terminal emulators.
For example, reading a dump of plain text is 4x faster compared to iTerm and
Kitty, and 2x faster than Terminal.app. Alacritty is very fast but we're still
around the same speed (give or take) and our app experience is much more
feature rich.
Note
Despite being very fast, there is a lot of room for improvement here.
Richer Windowing Features
The Mac and Linux (build with GTK) apps support multi-window, tabbing, and splits.
Native Platform Experiences
Ghostty is a cross-platform terminal emulator but we don't aim for a least-common-denominator experience. There is a large, shared core written in Zig but we do a lot of platform-native things:
- The macOS app is a true SwiftUI-based application with all the things you would expect such as real windowing, menu bars, a settings GUI, etc.
- macOS uses a true Metal renderer with CoreText for font discovery.
- The Linux app is built with GTK.
There are more improvements to be made. The macOS settings window is still a work-in-progress. Similar improvements will follow with Linux.
Cross-platform libghostty for Embeddable Terminals
In addition to being a standalone terminal emulator, Ghostty is a
C-compatible library for embedding a fast, feature-rich terminal emulator
in any 3rd party project. This library is called libghostty.
Due to the scope of this project, we're breaking libghostty down into
separate actually libraries, starting with libghostty-vt. The goal of
this project is to focus on parsing terminal sequences and maintaining
terminal state. This is covered in more detail in this
blog post.
libghostty-vt is already available and usable today for Zig and C and
is compatible for macOS, Linux, Windows, and WebAssembly. At the time of
writing this, the API isn't stable yet and we haven't tagged an official
release, but the core logic is well proven (since Ghostty uses it) and
we're working hard on it now.
The ultimate goal is not hypothetical! The macOS app is a libghostty consumer.
The macOS app is a native Swift app developed in Xcode and main() is
within Swift. The Swift app links to libghostty and uses the C API to
render terminals.
Crash Reports
Ghostty has a built-in crash reporter that will generate and save crash
reports to disk. The crash reports are saved to the $XDG_STATE_HOME/ghostty/crash
directory. If $XDG_STATE_HOME is not set, the default is ~/.local/state.
Crash reports are not automatically sent anywhere off your machine.
Crash reports are only generated the next time Ghostty is started after a crash. If Ghostty crashes and you want to generate a crash report, you must restart Ghostty at least once. You should see a message in the log that a crash report was generated.
Note
Use the
ghostty +crash-reportCLI command to get a list of available crash reports. A future version of Ghostty will make the contents of the crash reports more easily viewable through the CLI and GUI.
Crash reports end in the .ghosttycrash extension. The crash reports are in
Sentry envelope format. You can
upload these to your own Sentry account to view their contents, but the format
is also publicly documented so any other available tools can also be used.
The ghostty +crash-report CLI command can be used to list any crash reports.
A future version of Ghostty will show you the contents of the crash report
directly in the terminal.
To send the crash report to the Ghostty project, you can use the following CLI command using the Sentry CLI:
SENTRY_DSN=https://e914ee84fd895c4fe324afa3e53dac76@o4507352570920960.ingest.us.sentry.io/4507850923638784 sentry-cli send-envelope --raw <path to ghostty crash>
Warning
The crash report can contain sensitive information. The report doesn't purposely contain sensitive information, but it does contain the full stack memory of each thread at the time of the crash. This information is used to rebuild the stack trace but can also contain sensitive data depending on when the crash occurred.