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author | Kristian Høgsberg <krh@bitplanet.net> | 2010-06-07 12:22:48 -0400 |
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committer | Kristian Høgsberg <krh@bitplanet.net> | 2010-06-07 12:22:48 -0400 |
commit | a7f258221a7dcc9dc7034203e20d9a50bfa8c621 (patch) | |
tree | d839a892130bcb5d60e9e67a872ba6b8c90d30ae /spec | |
parent | 1292383025d2e5b9c0f54046c94f7ec1bbed2493 (diff) |
Add spec document in progress
Diffstat (limited to 'spec')
-rw-r--r-- | spec/Makefile | 9 | ||||
-rw-r--r-- | spec/main.tex | 243 |
2 files changed, 252 insertions, 0 deletions
diff --git a/spec/Makefile b/spec/Makefile new file mode 100644 index 0000000..bbb81ff --- /dev/null +++ b/spec/Makefile @@ -0,0 +1,9 @@ +include ../config.mk + +all : main.pdf + +main.pdf : main.tex + pdflatex main.tex + +clean : + rm -f main.pdf main.aux main.log diff --git a/spec/main.tex b/spec/main.tex new file mode 100644 index 0000000..2adf296 --- /dev/null +++ b/spec/main.tex @@ -0,0 +1,243 @@ +\documentclass{article} +\usepackage{palatino} + +\author{Kristian Høgsberg\\ +\texttt{krh@bitplanet.net} +} + +\title{The Wayland Display Server} + +\begin{document} + +\maketitle + +\section{Wayland Overview} + + - wayland is a protocol for a new display server. + + - wayland is an implementation + +\subsection{Replacing X11} + +Over the last 10 years, a lot of functionality have slowly moved out +of the X server and into libraries or kernel drivers. It started with +freetype and fontconfig providing an alternative to the core X fonts +and direct rendering OpenGL as a graphics driver in a client side +library. Then cairo came along and provided a modern 2D rendering +library independent of X and compositing managers took over control of +the rendering of the desktop. Recently with GEM and KMS in the Linux +kernel, we can do modesetting outside X and schedule several direct +rendering clients. The end result is a highly modular graphics stack. + +Wayland is a new display server building on top of all those +components. We’re trying to distill out the functionality in the X +server that is still used by the modern Linux desktop. This turns out +to be not a whole lot. Applications can allocate their own off-screen +buffers and render their window contents by themselves. In the end, +what’s needed is a way to present the resulting window surface to a +compositor and a way to receive input. This is what Wayland provides, +by piecing together the components already in the eco-system in a +slightly different way. + +X will always be relevant, in the same way Fortran compilers and VRML +browsers are, but it’s time that we think about moving it out of the +critical path and provide it as an optional component for legacy +applications. + + +\section{Wayland protocol} + +\subsection{Basic Principles} + +The wayland protocol is a asynchronous object oriented protocol. All +requests are method invocations on some object. The request include +an object id that uniquely identifies an object on the server. Each +object implements an interface and the requests include an opcode that +identifies which method in the interface to invoke. + +The wire protocol is determined from the C prototypes of the requests +and events. There is a straight forward mapping from the C types to +packing the bytes in the request written to the socket. It is +possible to map the events and requests to function calls in other +languages, but that hasn't been done at this point. + +The server sends back events to the client, each event is emitted from +an object. Events can be error conditions. The event includes the +object id and the event opcode, from which the client can determine +the type of event. Events are generated both in repsonse to a request +(in which case the request and the event constitutes a round trip) or +spontanously when the server state changes. + + - state is broadcast on connect, events sent out when state + change. client must listen for these changes and cache the state. + no need (or mechanism) to query server state. + + - server will broadcast presence of a number of global objects, + which in turn will broadcast their current state + +\subsection{Connect Time} + + - no fixed format connect block, the server emits a bunch of events + at connect time + + - presence events for global objects: output, compositor, input devices + +\subsection{Security and Authentication} + + - mostly about access to underlying buffers, need new drm auth + mechanism (the grant-to ioctl idea), need to check the cmd stream? + + - getting the server socket depends on the compositor type, could be + a system wide name, through fd passing on the session dbus. or the + client is forked by the compositor and the fd is already opened. + +\subsection{Creating Objects} + +\begin{itemize} +\item client allocates object ID, uses range protocol +\item server tracks how many IDs are left in current range, sends new + range when client is about to run out. +\end{itemize} + +\subsection{Compositor} + +\begin{itemize} +\item a global object +\item broadcasts drm file name, or at least a string like drm:/dev/card0 +\item commit/ack/frame protocol +\end{itemize} + +\subsection{Surface} + +created by the client +\begin{itemize} +\item attach +\item copy +\item damage +\item destroy +\item input region, opaque region +\item set cursor +\end{itemize} + +\subsection{Input Group} + +global object + +\begin{itemize} +\item - input group, keyboard, mouse +\item keyboard map, change events +\item pointer motion +\item enter, leave, focus +\item xkb on wayland +\item multi pointer wayland +\end{itemize} + + +\subsection{Output} + + - global objects + - a connected screen + - laid out in a big coordinate system + - basically xrandr over wayland + +\section{Types of compositors} + +\subsection{System Compositor} + + - ties in with graphical boot + - hosts different types of session compositors + - lets us switch between multiple sessions (fast user switching, + secure/personal desktop switching) + - multiseat + - linux implementation using libudev, egl, kms, evdev, cairo + - for fullscreen clients, the system compositor can reprogram the + video scanout address to source fromt the client provided buffer. + +\subsection{Session Compositor} + + - nested under the system compositor. nesting is feasible because + protocol is async, roundtrip would break nesting + - gnome-shell + - moblin + - compiz? + - kde compositor? + - text mode using vte + - rdp session + - fullscreen X session under wayland + - can run without system compositor, on the hw where it makes + sense + - root window less X server, bridging X windows into a wayland + session compositor + +\subsection{Embbedding Compositor} + +X11 lets clients embed windows from other clients, or lets client copy +pixmap contents rendered by another client into their window. This is +often used for applets in a panel, browser plugins and similar. +Wayland doesn't directly allow this, but clients can communicate GEM +buffer names out-of-band, for example, using d-bus or as command line +arguments when the panel launches the applet. Another option is to +use a nested wayland instance. For this, the wayland server will have +to be a library that the host application links to. The host +application will then pass the wayland server socket name to the +embedded application, and will need to implement the wayland +compositor interface. The host application composites the client +surfaces as part of it's window, that is, in the web page or in the +panel. The benefit of nesting the wayland server is that it provides +the requests the embedded client needs to inform the host about buffer +updates and a mechanism for forwarding input events from the host +application. + + - firefox embedding flash by being a special purpose compositor to + the plugin + +\section{Implementation} + +what's currently implemented + +\subsection{Wayland Server Library} + +\texttt{libwayland-server.so} + + - implements protocol side of a compositor + + - minimal, doesn't include any rendering or input device handling + + - helpers for running on egl and evdev, and for nested wayland + +\subsection{Wayland Client Library} + +\texttt{libwayland.so} + + - minimal, designed to support integration with real toolkits such as + Qt, GTK+ or Clutter. + + - doesn't cache state, but lets the toolkits cache server state in + native objects (GObject or QObject or whatever). + +\subsection{Wayland System Compositor} + + - implementation of the system compositor + + - uses libudev, eagle (egl), evdev and drm + + - integrates with ConsoleKit, can create new sessions + + - allows multi seat setups + + - configurable through udev rules and maybe /etc/wayland.d type thing + +\subsection{X Server Session} + + - xserver module and driver support + + - uses wayland client library + + - same X.org server as we normally run, the front buffer is a wayland + surface but all accel code, 3d and extensions are there + + - when full screen the session compositor will scan out from the X + server wayland surface, at which point X is running pretty much as it + does natively. + +\end{document} |