Client-side Wayland connector

Overview

Connection to the Wayland compositor is achieved by the default_connect() function, which provides you with a WlDisplay and an EventQueue.

From the display, you'll retrieve the registry, from which you can instanciate the globals you need. This step being really similar in most cases, this crate contains an utility struct EnvHandler which can do this job for you. See its documentation for details.

You then register your handlers for events to the event queue, and integrate it in your main event loop.

Handlers and event queues

This crate mirrors the callback-oriented design of the Wayland C library by using handler structs: each wayland type defines a Handler trait in its module, which one method for each possible event this object can receive.

To use it, you need to build a struct (or enum) that will implement all the traits for all the events you are interested in. All methods of handler traits provide a default implementation foing nothing, so you don't need to write empty methods for events you want to ignore. You also need to declare the handler capability for your struct using the declare_handler!(..) macro. A single struct can be handler for several wayland interfaces at once.

Example of handler

/*  writing a handler for an wl_foo interface */
// import the module of this interface
use wl_foo;

struct MyHandler { /* some fields to store state */ }

// implement handerl trait:
impl wl_foo::Handler for MyHandler {
    fn an_event(&mut self,
                evqh: &mut EventQueueHandle,
                me: &wl_foo::WlFoo,
                arg1, arg2, // the actual args of the event
    ) {
        /* handle the event */
    }
}

// declare the handler capability
// this boring step is necessary because Rust's type system is
// not yet magical enough
declare_handler!(MyHandler, wl_foo::Handler, wl_foo::WlFoo);

Event Queues and handlers

In your initialization code, you'll need to instanciate your handler and give it to the event queue:

let handler_id = event_queue.add_handler(MyHandler::new());

Then, you can register your wayland objects to this handler:

// This type info is necessary for safety, as at registration
// time the event_queue will check that the handler you
// specified using handler_id has the same type as provided
// as argument, and that this type implements the appropriate
// handler trait.
event_queue.register::<_, MyHandler>(&my_object, handler_id);

You can have several handlers in the same event queue, but they cannot share their state without synchronisation primitives like Arc, Mutex and friends, so if two handlers need to share some state, you should consider building them as a single struct.

A given wayland object can only be registered to a single handler at a given time, re-registering it to a new handler will overwrite the previous configuration.

Handlers can be created, and objects registered to them from within a handler method, using the &EventQueueHandle argument.

Event loop integration

Once this setup is done, you can integrate the event queue to the main event loop of your program:

loop {
    // flush events to the server
    display.flush().unwrap();
    // receive events from the server and dispatch them
    // to handlers (might block)
    event_queue.dispatch().unwrap();
}

For more precise control of the flow of the event queue (and importantly non-blocking options), see EventQueue documentation.

Protocols integration

This crate provides the basic primitives as well as the core wayland protocol (in the protocol module), but other protocols can be integrated from XML descriptions.