5bfdb1b9cf
It's here, the long-foretold and long-procrastinated renderer rework!
Hopefully this makes it easier to adapt and modify the renderer in the
future and ensures feature parity between Metal and OpenGL. Despite
having been a lot of work to write initially, with the abstraction layer
in place I feel like working on the renderer will be a much more
pleasant experience going forward.
## Key points
- CPU-side renderer logic is now mostly unified via a generic
`Renderer`.
- A graphics API abstraction layer over OpenGL and Metal has been
introduced.
- Minimum OpenGL version bumped to `4.3`, so can no longer be run on
macOS; I used the nix VM stuff for my testing during development. (Edit
by @mitchellh: Note for readers that Ghostty still works on macOS, but
the OpenGL backend doesn't, only the Metal one)
- The OpenGL backend now supports linear blending! Woohoo! The default
`alpha-blending` has been updated to `linear-corrected` since it's
essentially a strict improvement over `native`. The default on macOS is
still `native` though to match other mac apps in appearance, since macOS
users are more sensitive to text appearance.
- Custom shaders can now be hot reloaded.
- The background color is once again drawn by us, so custom shaders can
interact with it properly. In general, custom shaders should be a little
more robust.
## The abstraction layer
The general hierarchy of the abstraction layer is as such:
```
[ GraphicsAPI ] - Responsible for configuring the runtime surface
| | and providing render `Target`s that draw to it,
| | as well as `Frame`s and `Pipeline`s.
| V
| [ Target ] - Represents an abstract target for rendering, which
| could be a surface directly but is also used as an
| abstraction for off-screen frame buffers.
V
[ Frame ] - Represents the context for drawing a given frame,
| provides `RenderPass`es for issuing draw commands
| to, and reports the frame health when complete.
V
[ RenderPass ] - Represents a render pass in a frame, consisting of
: one or more `Step`s applied to the same target(s),
[ Step ] - - - - each describing the input buffers and textures and
: the vertex/fragment functions and geometry to use.
:_ _ _ _ _ _ _ _ _ _/
v
[ Pipeline ] - Describes a vertex and fragment function to be used
for a `Step`; the `GraphicsAPI` is responsible for
these and they should be constructed and cached
ahead of time.
[ Buffer ] - An abstraction over a GPU buffer.
[ Texture ] - An abstraction over a GPU texture.
```
More specific documentation can be found on the relevant structures.
## Miscellany
Renderers (which effectively just means the generic renderer) are now
expected to only touch GPU resources in `init`, certain lifecycle
functions such as the `displayRealized`/`displayUnrealized` callbacks
from GTK-- and `drawFrame`; and are also expected to be thread-safe.
This allows the renderer thread to build the CPU-side buffers
(`updateFrame`) even if we can only *draw* from the app thread.
Because of this change, we can draw synchronously from the main thread
on macOS when necessary to always have a frame of the correct size
during a resize animation. This was necessary to allow the background to
be drawn by our GPU code (instead of setting a background color on the
layer) while still avoiding holes during resize.
The OpenGL backend now theoretically has access to multi-buffering, but
it's disabled (by setting the buffer count to 1) because it
synchronously waits for frames to complete anyway which means that the
extra buffers were just a waste of memory.
## Validation
To validate that there are no significant or obvious problems, I
exercised both backends with a variety of configurations, and visually
inspected the results. Everything looks to be in order.
The images are available in a gist here:
https://gist.github.com/qwerasd205/c1bd3e4c694d888e41612e53c0560179
## Memory
Here's a comparison of memory usage for ReleaseFast builds on macOS,
between `main` and this branch.
Memory figures given are values from Activity Monitor measuring windows
of the same size, with two tabs with 3 splits each.
||Before|After|
|-:|-|-|
|**Memory**|247.9 MB|224.2 MB|
|**Real Memory**|174.4 MB|172.5 MB|
Happily, the rework has slightly *reduced* the memory footprint- likely
due to removing the overhead of `CAMetalLayer`. (The footprint could be
reduced much further if we got rid of multi-buffering and satisfied
ourselves with blocking for each frame, but that's a discussion for
another day.)
If someone could do a similar comparison for Linux, that'd be much
appreciated!
## Notes / future work
- There are a couple structures that *can* be unified using the
abstraction layer, but I haven't gotten around to unifying yet.
Specifically, in `renderer/(opengl|metal)/`, there's `cell.zig` and
`image.zig`, both of which are substantially identical between the two
backends. `shaders.zig` may also be a candidate for unification, but
that might be *overly* DRY.
- ~~I did not double-check the documentation for config options, which
may mention whether certain options can be hot-reloaded; if it does then
that will need to be updated.~~ Fixed: be5908f
- The `fragCoord` for custom shaders originates at the top left for
Metal, but *bottom* left for OpenGL; fixing this will be a bit annoying,
since the screen texture is likewise vertically flipped between the two.
Some shaders rely on the fragcoord for things like falling particles, so
this does need to be fixed.
- `Target` should be improved to support multiple types of targets right
now it only represents a framebuffer or iosurface, but it should also be
able to represent a texture; right now a kind of messy tagged union is
used so that steps can accept both.
- Custom shader cursor uniforms (#6912) and terminal background images
(#4226, #5233) should be much more straightforward to implement on top
of this rework, and I plan to make follow-up PRs for them once this is
merged.
- I *do* want to do a rework of the pipelines themselves, since the way
we're rendering stuff is a bit messy currently, but this is already a
huge enough PR as it is- so for now the renderer still uses the same
rendering passes that Metal did before.
- We should probably add a system requirements section to the README
where we can note the minimum required OpenGL version of `4.3`, any even
slightly modern Linux system will support this, but it would be good to
document it somewhere user-facing anyway.
# TODO BEFORE MERGE
- [x] Have multiple people test this on both macOS and linux.
- [ ] ~~Have someone with a better dev setup on linux check for memory
leaks and other problems.~~ (Skipped, will merge and let tip users
figure this out, someone should *specifically* look for memory leaks
before the next versioned release though.)
- [x] Address any code review feedback.
Ghostty
Fast, native, feature-rich terminal emulator pushing modern features.
About
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Documentation
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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.
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.
This 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.
This step encompasses expanding libghostty support to more platforms
and more use cases. At the time of writing this, libghostty is very
Mac-centric -- particularly around rendering -- and we have work to do to
expand this to other platforms.
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 when the crash occurred.
Developing Ghostty
See the documentation on the Ghostty website for
building Ghostty from a source tarball.
Building Ghostty from a Git checkout is very similar, except you want to
omit the -Doptimize flag to build a debug build, and you may require
additional dependencies since the source tarball includes some processed
files that are not in the Git repository.
On Linux or macOS, you can use zig build -Dapp-runtime=glfw run for a quick
GLFW-based app for a faster development cycle while developing core
terminal features. Note that this app is missing many features and is also
known to crash in certain scenarios, so it is only meant for development
tasks.
Other useful commands:
zig build testfor running unit tests.zig build test -Dtest-filter=<filter>for running a specific subset of those unit testszig build run -Dconformance=<name>runs a conformance test case from theconformancedirectory. Thenameis the name of the file. This runs in the current running terminal emulator so if you want to check the behavior of this project, you must run this command in Ghostty.
Extra Dependencies
Building Ghostty from a Git checkout on Linux requires some additional dependencies:
blueprint-compiler
macOS users don't require any additional dependencies.
Note
This only applies to building from a Git checkout. This section does not apply if you're building from a released source tarball. For source tarballs, see the website.
Xcode Version and SDKs
Building the Ghostty macOS app requires that Xcode, the macOS SDK, and the iOS SDK are all installed.
A common issue is that the incorrect version of Xcode is either
installed or selected. Use the xcode-select command to
ensure that the correct version of Xcode is selected:
sudo xcode-select --switch /Applications/Xcode-beta.app
Important
Main branch development of Ghostty is preparing for the next major macOS release, Tahoe (macOS 26). Therefore, the main branch requires Xcode 26 and the macOS 26 SDK.
You do not need to be running on macOS 26 to build Ghostty, you can still use Xcode 26 beta on macOS 15 stable.
Linting
Prettier
Ghostty's docs and resources (not including Zig code) are linted using Prettier with out-of-the-box settings. A Prettier CI check will fail builds with improper formatting. Therefore, if you are modifying anything Prettier will lint, you may want to install it locally and run this from the repo root before you commit:
prettier --write .
Make sure your Prettier version matches the version of Prettier in devShell.nix.
Nix users can use the following command to format with Prettier:
nix develop -c prettier --write .
Alejandra
Nix modules are formatted with Alejandra. An Alejandra CI check will fail builds with improper formatting.
Nix users can use the following command to format with Alejandra:
nix develop -c alejandra .
Non-Nix users should install Alejandra and use the following command to format with Alejandra:
alejandra .
Make sure your Alejandra version matches the version of Alejandra in devShell.nix.
Updating the Zig Cache Fixed-Output Derivation Hash
The Nix package depends on a fixed-output derivation that manages the Zig package cache. This allows the package to be built in the Nix sandbox.
Occasionally (usually when build.zig.zon is updated), the hash that
identifies the cache will need to be updated. There are jobs that monitor the
hash in CI, and builds will fail if it drifts.
To update it, you can run the following in the repository root:
./nix/build-support/check-zig-cache-hash.sh --update
This will write out the nix/zigCacheHash.nix file with the updated hash
that can then be committed and pushed to fix the builds.