vtabs

A proof-of-concept terminal emulator with vertical tabs, built on libghostty-vt and GTK4/libadwaita.

The sidebar holds the window controls, a new-tab button, and one row per tab — the layout Zen Browser uses for vertical tabs — with the terminal inset to its right.

Quick start

nix develop          # Zig 0.16 + GTK4 + libadwaita, no host toolchain needed
zig build run

Everything is pinned by flake.nix; nothing needs to be installed on the host.

Installing

mise run install     # builds release, installs into ~/.local
mise run uninstall

That puts the binary in ~/.local/libexec/vtabs, a launcher on ~/.local/bin, a desktop entry in ~/.local/share/applications, and the icon in the hicolor theme, then refreshes the desktop and icon caches. mise tasks lists the rest (build, run, fmt, screenshot).

Two things the installer has to handle that a normal install wouldn't:

• A launcher, not a symlink. The binary links against GTK in the Nix store and has an RPATH, so it runs anywhere — but it still needs to be pointed at GTK's GSettings schemas and icon themes, or it aborts on a missing schema. A desktop launcher starts the app with a minimal environment, so those paths are baked into the launcher script. They are read out of the dev shell at install time rather than hardcoded, so they can't drift from the flake.
• Nix GC roots. The installed app depends on store paths that nix-collect-garbage would otherwise be free to delete, which would break it later with no obvious connection to the command that did it. Install pins every store path in the binary's RPATH; uninstall releases them.

Which "libghostty" this uses, and why

Ghostty ships two different C APIs, and only one of them is usable here:

	include/ghostty.h	include/ghostty/vt.h
name	"libghostty-internal"	libghostty-vt
scope	whole terminal incl. renderer	VT core only
platforms	GHOSTTY_PLATFORM_MACOS, GHOSTTY_PLATFORM_IOS	any
intended for	Ghostty's own macOS app	external embedders

ghostty.h is the one that would hand you a ready-made terminal surface, but it has no Linux platform tag at all — its ghostty_platform_e enum only knows macOS and iOS, and its own header says it is "tailored to the needs of the macOS app". On Linux, Ghostty does not embed itself through that API; it builds its GTK apprt directly into the binary.

So this project uses libghostty-vt, the API Ghostty documents for external embedders. That means we get, for free and battle-tested:

• escape sequence parsing and full terminal state
• screen, scrollback, line wrapping, and reflow on resize
• key and mouse event encoding (including the Kitty keyboard protocol)
• paste safety checking and bracketed paste encoding

and we supply everything above it: process management, rendering, and the UI.

We consume it as a Zig module rather than through the C ABI. Ghostty's build.zig detects that it is being used as a dependency and, in that mode, builds only libghostty-vt — no GTK, no executable — so zig build pulls in just the VT core.

Architecture

main.zig       AdwApplication, CSS loading
Window.zig     sidebar + GtkStack of views, tab management, shortcuts
View.zig       one tab's content: its panes, their layout, and drag handling
Layout.zig     the split tree: nodes, rearranging, GtkPaned materialization
Pane.zig       a terminal plus its header, drag source, and drop target
Terminal.zig   GtkDrawingArea: Cairo/Pango renderer + input handling
Session.zig    libghostty-vt Terminal + parser, fed by the PTY
Pty.zig        openpt/fork/exec, controlling terminal setup
key.zig        GDK keyval -> libghostty-vt key mapping
theme.zig      colors libghostty-vt has no opinion about

A tab is a view, and a view holds one or more terminal panes arranged in a binary split tree: every interior node is a split with an orientation, every leaf is a pane. That is what allows the layouts a single shared orientation can't express — three panes in a row, drag the rightmost to the bottom, and you get two on top with one spanning the full width beneath them.

Each split node owns a GtkPaned, so dividers are draggable and every split remembers its position as a ratio rather than a pixel count. The ratio is the source of truth: it is re-applied whenever the available space changes, so proportions survive window resizes, and only user drags update it.

Where a drop lands depends on how close it is to the view's own border. Near an edge of the window the pane is placed against the whole layout and spans it; anywhere else it splits just the pane under the pointer. That single rule gives both "put this across the bottom" and "split this one in half".

Panes and split nodes each hold a strong reference to their own widget, so detaching and reattaching during a rearrangement never finalizes anything. Running terminals keep their scrollback and processes straight through a move.

Drags rearrange live. Each time the drop target changes, the move is applied for real, so the layout under the cursor is always the layout you will get — there is no separate drop indicator because the view itself is the preview. Cancelling a drag puts the pane back: only the dragged pane ever moves, so the rest of the tree is unchanged and re-inserting it beside its original sibling restores the original shape.

Two design choices worth calling out:

No IO thread. The PTY is read on the GLib main loop through a unix fd watch (g_unix_fd_add). Terminal state is therefore only ever touched from the main thread, so the renderer reads the screen with no locking. Ghostty itself uses a dedicated IO thread; that is the right answer for a real terminal, but this is dramatically simpler and is not a bottleneck at interactive speeds.

No GPU renderer. Ghostty rasterizes glyphs into an atlas and draws on the GPU. Here, each frame walks the visible rows, groups cells into runs of identical style, and hands each run to Pango. That is far more work per frame in principle, but a terminal grid is small.

What works

• Your login shell (from the passwd database, not $SHELL) on a real PTY, started as a login shell, with a controlling terminal so job control, Ctrl-C and SIGWINCH behave
• Full SGR rendering: 16/256/true color, bold, italic, underline, strikethrough, inverse, and the bright-on-bold convention
• Block / bar / underline / hollow cursor styles
• Scrollback via mouse wheel; typing snaps back to the prompt
• Resize reflows the grid and notifies the child
• Window title (OSC 0/2) becomes the pane header and tab label; the tab shows its pane count once a view holds more than one
• Tabs: create, close, switch; closing the last one closes the window
• Multiple terminals per tab in an arbitrary split tree, rearranged by keyboard or by dragging a pane's header, with draggable dividers between them; closing the last pane in a view closes its tab

Shortcuts

Ctrl+Shift+T	new tab
Ctrl+Shift+E	new terminal in the current tab
Ctrl+Shift+W	close the focused terminal (closes the tab with its last one)
Ctrl+Shift+←/→/↑/↓	move the focused terminal within its view
Ctrl+Shift+V	paste (bracketed-paste aware, refuses unsafe pastes)
Ctrl+PageUp/PageDown	previous / next tab
Alt+1..Alt+8	jump to tab N, Alt+9 jumps to the last

Dragging a pane by its header does the same thing as the arrow shortcuts: the edge you drop against decides both the order and the view's orientation. The header is the drag handle rather than the whole pane so that dragging never competes with the terminal's own mouse handling.

Not implemented

This is a proof of concept, and the following are deliberately absent:

• Mouse selection and copy. libghostty-vt provides the selection and mouse-encoding primitives, but nothing here is wired to them yet, so there is no way to copy text. Paste works.
• Ligatures and complex shaping. Each run is drawn independently at a fixed grid offset, so text that needs shaping across cell boundaries won't look right.
• Moving panes between tabs. Panes can only be rearranged within their own view.
• Saved layouts. A view's arrangement lives only as long as the tab.
• Kitty graphics, hyperlinks, tab reordering, config file.
• Custom terminfo. TERM is reported as xterm-256color rather than ghostty, since we don't install a terminfo entry.

Development

./b.sh wraps nix develop --command zig build and strips the enormous command line Zig prints on failure.

mise run screenshot out.png "text to type" (or ./shot.sh directly) runs the app inside a throwaway headless Sway and screenshots it. This keeps UI checks entirely out of your real Wayland session — nothing appears on screen, and it works while the session is locked.

One caveat when driving it: wtype loses the first keystroke of every invocation while the compositor adopts its freshly uploaded keymap, so scripted input should begin with a throwaway key. That is a quirk of the injection tool, not of the terminal.