gpui

Define actions with the actions! macro or #[derive(Action)], bind keys with cx.bind_keys() using KeyBinding entries, and handle them with .on_action() on elements. Use key_context() to make bindings context-aware so the same key can trigger different actions.

Use cx.spawn for foreground tasks that update entities and cx.background_spawn for CPU-intensive work on worker threads. Chain background results back to the foreground with .then(cx.spawn(...)) since entities can only be updated on the UI thread.

App is the global context for entity creation and app-wide state, Window handles window-specific operations like painting and layout, and Context<T> is the entity-specific context for a component. AsyncApp and AsyncWindowContext are their async counterparts used inside spawned tasks.

Implement the Element trait with RequestLayoutState and PrepaintState associated types plus the request_layout, prepaint, and paint methods. Create hitboxes in prepaint, paint children before your own content, and handle mouse events in the paint phase.

cx.defer_in schedules a callback on the current entity, so GPUI re-acquires that entity's lock to run it. Calling entity.update() on the same entity inside the callback re-enters the lock and panics; use the provided &mut reference directly instead.

Use the #[gpui::test] attribute with TestAppContext for logic tests and VisualTestContext for rendering tests. You can open windows, dispatch synthetic mouse events, and assert on entity state within the test context.