Ghostling — libghostty Terminal Emulator

Skill by ara.so — Daily 2026 Skills collection.

Ghostling is a minimal viable terminal emulator built on libghostty-vt, the embeddable C library extracted from Ghostty. It uses Raylib for windowing/rendering and lives in a single C file. The project demonstrates how to wire libghostty-vt's VT parsing, terminal state, and render-state API to any 2D or GPU renderer.

What libghostty-vt Provides

• VT sequence parsing (SIMD-optimized)
• Terminal state: cursor, styles, text reflow, scrollback
• Render state management (what cells changed and how to draw them)
• Unicode / multi-codepoint grapheme handling
• Kitty keyboard protocol, mouse tracking, focus reporting
• Zero dependencies (not even libc) — WASM-compatible

libghostty-vt does NOT provide: windowing, rendering, PTY management, tabs, splits, or configuration.

Requirements

Build & Run

# Clone
git clone https://github.com/ghostty-org/ghostling.git
cd ghostling

# Debug build (slow — safety checks enabled)
cmake -B build -G Ninja
cmake --build build
./build/ghostling

# Release build (optimized)
cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build
./build/ghostling

After first configure, only the build step is needed:

cmake --build build

Warning: Debug builds are very slow due to Ghostty's safety/correctness assertions. Always benchmark with Release builds.

Project Structure

ghostling/
├── main.c          # Entire terminal implementation (single file)
├── CMakeLists.txt  # Build config; fetches libghostty-vt + Raylib
└── demo.gif

Core libghostty-vt API Patterns

All implementation lives in main.c. Below are the key patterns extracted from it.

1. Initialize the Terminal

#include "ghostty.h"  // provided by libghostty-vt via CMake

// Create terminal with cols x rows cells
ghostty_terminal_t *terminal = ghostty_terminal_new(
    &(ghostty_terminal_config_t){
        .cols = cols,
        .rows = rows,
    }
);
if (!terminal) { /* handle error */ }

2. Write Data from PTY into the Terminal

// Read from PTY fd, feed raw bytes to libghostty-vt
ssize_t n = read(pty_fd, buf, sizeof(buf));
if (n > 0) {
    ghostty_terminal_write(terminal, buf, (size_t)n);
}

3. Send Keyboard Input

// libghostty-vt encodes the correct escape sequences
ghostty_key_event_t ev = {
    .key       = GHOSTTY_KEY_A,          // key enum
    .mods      = GHOSTTY_MODS_CTRL,      // modifier flags
    .action    = GHOSTTY_ACTION_PRESS,
    .composing = false,
};

uint8_t out[64];
size_t  out_len = 0;
ghostty_terminal_key(terminal, &ev, out, sizeof(out), &out_len);

// Write encoded bytes to PTY
if (out_len > 0) write(pty_fd, out, out_len);

4. Send Mouse Events

ghostty_mouse_event_t mev = {
    .x      = cell_col,   // cell column
    .y      = cell_row,   // cell row
    .button = GHOSTTY_MOUSE_LEFT,
    .action = GHOSTTY_MOUSE_PRESS,
    .mods   = GHOSTTY_MODS_NONE,
};

uint8_t out[64];
size_t  out_len = 0;
ghostty_terminal_mouse(terminal, &mev, out, sizeof(out), &out_len);
if (out_len > 0) write(pty_fd, out, out_len);

5. Resize the Terminal

ghostty_terminal_resize(terminal, new_cols, new_rows);
// libghostty-vt handles text reflow automatically
// Send SIGWINCH to the child process after this
struct winsize ws = { .ws_col = new_cols, .ws_row = new_rows };
ioctl(pty_fd, TIOCSWINSZ, &ws);
kill(child_pid, SIGWINCH);

6. Render: Walk the Render State

The render state API tells you exactly which cells changed and how to draw them — no need to redraw everything every frame.

// Get render state handle
ghostty_render_state_t *rs = ghostty_terminal_render_state(terminal);

// Begin a render pass (snapshot current state)
ghostty_render_state_begin(rs);

// Iterate dirty cells
ghostty_render_cell_iter_t iter = {0};
ghostty_render_cell_t      cell;

while (ghostty_render_state_next_cell(rs, &iter, &cell)) {
    // cell.col, cell.row      — grid position
    // cell.codepoint          — Unicode codepoint (0 = empty)
    // cell.fg.r/g/b           — foreground RGB
    // cell.bg.r/g/b           — background RGB
    // cell.attrs.bold         — bold flag
    // cell.attrs.italic       — italic flag
    // cell.attrs.reverse      — reverse video

    // Example: draw with Raylib
    Color fg = { cell.fg.r, cell.fg.g, cell.fg.b, 255 };
    Color bg = { cell.bg.r, cell.bg.g, cell.bg.b, 255 };

    Rectangle rect = {
        .x      = cell.col * cell_width,
        .y      = cell.row * cell_height,
        .width  = cell_width,
        .height = cell_height,
    };
    DrawRectangleRec(rect, bg);

    if (cell.codepoint != 0) {
        char glyph[8] = {0};
        // encode codepoint to UTF-8 yourself or use a helper
        encode_utf8(cell.codepoint, glyph);
        DrawText(glyph, (int)rect.x, (int)rect.y, font_size, fg);
    }
}

// End render pass (marks cells as clean)
ghostty_render_state_end(rs);

7. Scrollback

// Scroll viewport up/down by N rows
ghostty_terminal_scroll(terminal, -3);  // scroll up 3
ghostty_terminal_scroll(terminal,  3);