Module backend

Backend (rendering/input) helpers

This module provides helpers for interaction with the operating system.

Module structure

The module is largely structured around three main aspects of interaction with the OS: session management, input handling, and graphics.

Session management

Session management relates to mechanisms allowing the compositor to access the resources it needs to function. It contains interaction with the login manager if any ((e)logind or seatd), as well as releasing those resources when TTY-switching. It is handled by the session module, gated by the backend_session cargo feature. You will generally need it to run your compositor directly on a TTY.

This module is tightly coupled with the udev module (gated by the backend_udev cargo feature), which allows the discovery of usable graphics and input devices on the system, using the udev system daemon.

Input handling

Input handling consists in discovering the various available input devices, and receiving all inputs events from it. Smithay is build to support different possible sources for that input data, with a generic API provided by the traits and types defined in the input module. An input provider following this API based on libinput is given in the libinput module, gated by the backend_libinput cargo feature. The winit backend (see below) also provides an input provider.

Graphics

Combining content from the clients and displaying it on the screen is the central role of a wayland compositor, and also one of its most complex tasks; several backend modules are dedicated to this task.

Smithay provides a rendering infrastructure built around graphics buffers: you retrieve buffers for your client, you composite them into a new buffer holding the contents of your desktop, that you will then submit to the hardware for display. The backbone of this infrastructure is structured around two modules:

• allocator contains generic traits representing the capability to allocate and convert graphical buffers, as well as an implementation of this capability using GBM (see its module-level docs for details).
• renderer provides traits representing the capability of graphics rendering using those buffers, as well as an implementation of this capability using GLes2 (see its module-level docs for details).

Alongside this backbone capability, Smithay also provides the drm module, which handles direct interaction with the graphical physical devices to setup the display pipeline and submit rendered buffers to the monitors for display. This module is gated by the backend_drm cargo feature.

The egl module provides the logic to setup an OpenGL context. It is used by the Gles2 renderer (which is based on OpenGL), and also provides the capability for clients to use the wl_drm-based hardware-acceleration provided by Mesa, a precursor to the linux_dmabuf Wayland protocol extension. Note that, at the moment, even clients using dma-buf still require that the wl_drm infrastructure is initialized to have hardware-acceleration.

X11 backend

Alongside this infrastructure, Smithay also provides an alternative backend based on x11rb, which makes it possible to run your compositor as an X11 client. This is generally quite helpful for development and debugging.

The X11 backend does not concern itself with what renderer is in use, allowing presentation to the window assuming you can provide it with a Dmabuf. The X11 backend is also an input provider, and is accessible in the x11 module, gated by the backend_x11 cargo feature.

Winit backend

Alongside this infrastructure, Smithay also provides an alternative backend based on winit, which makes it possible to run your compositor as a Wayland or X11 client. You are encouraged to use the X11 backend where possible since winit does not integrate into calloop too well. This backend is generally quite helpful for development and debugging. That backend is both a renderer and an input provider, and is accessible in the winit module, gated by the backend_winit cargo feature.

Modules

allocator

Buffer allocation and management.

drmbackend_drm

This module represents abstraction on top the linux direct rendering manager api (drm).

eglbackend_egl

Common traits and types for egl rendering

input

Common traits for input backends to receive input from.

libinputbackend_libinput

Implementation of input backend trait for types provided by libinput

renderer

Rendering functionality and abstractions

sessionbackend_session

Abstraction of different session APIs.

udevbackend_udev

udev related functionality for automated device scanning

vulkanbackend_vulkan

Types to initialize and use Vulkan.

winitbackend_winit

Implementation of backend traits for types provided by winit

x11backend_x11

Implementation of the backend types using X11.

Enums

SwapBuffersError

Error that can happen when swapping buffers.