The wasm core

Ghostty’s libghostty-vt owns terminal state. WebAssembly runs that core inside the browser or a headless host. The JavaScript host connects input, layout and a renderer to that native state.

PTY bytes → libghostty-vt → native screen and history
                                ↓
                         render-state damage
                                ↓
                          frame building
                                ↓
                   WebGPU / WebGL2 / Canvas / DOM

One terminal state

Parsing changes the active screen, cursor, modes and retained history. Selection, text reads and rendered output read that same native state. GhosttyRuntime loads the core. GhosttyTerminal exposes headless operations. TerminalSession adds the native session model, and Terminal supplies the DOM host.

The wasm build uses the official upstream revision recorded in the provenance file. That file records the compiler, source hashes and unpatched build recipe. Browser font drawing and protocol integrations remain host responsibilities.

The host and the worker

The main entry calls native operations synchronously after asynchronous creation and opening. The worker entry puts native execution and GPU rendering in a dedicated actor. Its operations return promises when the caller needs the worker’s acknowledgement. The DOM host stays on the page to own focus, pointer input and layout.

Frames and reads

write updates emulator state. Rendering follows the scheduler. onFrame observes submitted rows and submittedFrame gives observers a coherent frame. readLines reads live native state; visibleLines reads the last submitted viewport. Choose the read that matches the question you are asking.

The generated API documents GhosttyRuntime, GhosttyTerminal, TerminalSession and Terminal. Continue with damage tracking or worker execution.