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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<link href="wayland.css" rel="stylesheet" type="text/css">
<script type="text/javascript" src="generated-toc.js"></script>
<title>Wayland</title>
</head>
<body>
<h1><a href="/"><img src="wayland.png" alt="Wayland logo"></a></h1>
<h2>Wayland FAQ</h2>
<div id="generated-toc" class="generate_from_h3"></div>
<h3>Why fork the X server?</h3>
<p>
It's not an X server and not a fork. It's a protocol between a
compositor and its clients. The compositor sends input events to
the clients. The clients render locally and then communicate video
memory buffers and information about updates to those buffers back
to the compositor.
</p>
<h3>What is the license?</h3>
<p>
Wayland is licensed under the
<a href="https://cgit.freedesktop.org/wayland/wayland/tree/COPYING">MIT Expat license</a>.
</p>
<h3>Why duplicate all this work?</h3>
<p>
Wayland is not really duplicating much work. Where possible,
Wayland reuses existing drivers and infrastructure. One of the
reasons this project is feasible at all is that Wayland reuses the
DRI drivers, the kernel side GEM scheduler and kernel mode setting.
Wayland doesn't have to compete with other projects for drivers and
driver developers, it lives within the X.org, mesa and drm community
and benefits from all the hardware enablement and driver development
happening there.
</p>
<h3>What is the drawing API?</h3>
<p>
"Whatever you want it to be, honey". Wayland doesn't render on
behalf of the clients, it expects the clients to use whatever means
they prefer to render into a shareable buffer. When the client is
done, it informs the Wayland server of the new contents. The
current test clients use either Cairo software rendering, Cairo on
OpenGL or hardware-accelerated OpenGL directly. Additionally, media
frameworks can share their buffers directly with the server. As
long as you have a userspace driver library that will let you render
into a shareable buffer, you're good to go.
</p>
<h3>Is wayland replacing the X server?</h3>
<p>
Mostly, yes. User sessions are able to run under Wayland today, via
a number of compositors: Weston itself as well as Enlightenment,
GNOME Shell, KDE, and a number of others under development. With
most toolkits having Wayland ports, as well as frameworks such as
GStreamer and SDL, it's perfectly possible to run a purely native
Wayland session as your desktop.
</p>
<p>
That being said, there are some clients which rely on X11, and
always will be. To that end, XWayland provides a plugin for Wayland
compositors, running a real X server. This gives legacy clients a
real and compliant X11 platform to run on, displayed side by side
with native Wayland clients in your Wayland session.
</p>
<h3>Why not extend the X server?</h3>
<p>
Because for the first time we have a realistic chance of not
having to do that. It's entirely possible to incorporate the buffer
exchange and update models that Wayland is built on into X.
However, we have an option here of pushing X out of the hotpath
between clients and the hardware and making it a compatibility
option. What's different now is that a lot of infrastructure has
moved from the X server into the kernel (memory management, command
scheduling, mode setting) or libraries (cairo, pixman, freetype,
fontconfig, pango, etc) and there is very little left that has to
happen in a central server process.
</p>
<h3>What is wrong with X?</h3>
<p>
The problem with X is that... it's X. When you're an X server
there's a tremendous amount of functionality that you must support
to claim to speak the X protocol, yet nobody will ever use this.
For example, core fonts; this is the original font model that was how
your got text on the screen for the many first years of X11. This
includes code tables, glyph rasterization and caching, XLFDs
(seriously, XLFDs!). Also, the entire core rendering API that lets
you draw stippled lines, polygons, wide arcs and many more
state-of-the-1980s style graphics primitives. For many things we've
been able to keep the X.org server modern by adding extensions such
as XRandR, XRender and COMPOSITE and to some extent phase out less
useful extensions. But we can't ever get rid of the core rendering
API and much other complexity that is rarely used in a modern
desktop. With Wayland we can move the X server and all its legacy
technology to an optional code path.
</p>
<h3>What about the overhead of running X on wayland?</h3>
<p>
Most modern desktops already use an external compositing manager:
when the X server decides it needs to update content, it informs
this external process (usually your window manager), and allows it to
control the rendering entirely. Using XWayland is just the same as
this, but more efficient because the compositing manager doesn't have
to go back through the X server to display the content it rendered.
</p>
<h3>Is Wayland network transparent / does it support remote rendering?</h3>
<p>
No, that is outside the scope of Wayland. To support remote
rendering you need to define a rendering API, which is something
I've been very careful to avoid doing. The reason Wayland is so
simple and feasible at all is that I'm sidestepping this big task
and pushing it to the clients. It's an interesting challenge, a
very big task and it's hard to get right, but essentially orthogonal
to what Wayland tries to achieve.
</p>
<p>
This doesn't mean that remote rendering won't be possible with
Wayland, it just means that you will have to put a remote rendering
server on top of Wayland. One such server could be the X.org server,
but other options include an RDP server, a VNC server or somebody
could even invent their own new remote rendering model. Which is a
feature when you think about it; layering X.org on top of Wayland
has very little overhead, but the other types of remote rendering
servers no longer requires X.org, and experimenting with new
protocols is easier.
</p>
<p>
It is also possible to put a remoting protocol into a wayland
compositor, either a standalone remoting compositor or as a part of
a full desktop compositor. This will let us forward native Wayland
applications. The standalone compositor could let you log into a
server and run an application back on your desktop. Building the
forwarding into the desktop compositor could let you export or share
a window on the fly with a remote wayland compositor, for example, a
friend's desktop.
</p>
<h3>How to download and build Wayland?</h3>
<p>
See the <a href="building.html">build instructions</a>.
</p>
<h3>Why wasn't D-Bus used instead of the Wayland IPC mechanism?</h3>
<p>
I wanted to preserve some important properties from the X protocol:
the ability to queue up an event or request by just memcpy'ing into
the protocol out-buffer. That's what wl_connection_write does.
Furthermore, it lets us memcpy several messages into the buffer and
only write it all before we go back to blocking in the main loop.
Second, everything is explicitly asynchronous, which is a really
powerful feature in a protocol.
</p>
<h3>How can I replace Wayland's Window Manager?</h3>
<p>
The Wayland architecture integrates the display server, window
manager and compositor into one process. You can think of Wayland
as a toolkit for creating clients and compositors. It is not a
specific single compositor or window manager. If you want a
different window manager, you can write a new one. A 'libweston'
effort is underway in order to allow new environments to reuse
Weston's codebase and mechanics, whilst providing their own look
and feel.
</p>
<h3>Why does Wayland use EGL?</h3>
<p>
EGL is the only GL binding API that lets us avoid dependencies on
existing window systems, in particular X. GLX obviously pulls in X
dependencies and only lets us set up GL on X drawables. The
alternative is to write a Wayland specific GL binding API, say,
WaylandGL.
</p>
<p>
A more subtle point is that libGL.so includes the GLX symbols, so
linking to that library will pull in all the X dependencies. This
means that we can't link to full GL without pulling in the client
side of X, so Weston uses OpenGL ES to render. This also enables
Weston to run on GPUs which don't support the full OpenGL API.
</p>
<p>
As detailed above, clients are however free to use whichever
rendering API they like.
</p>
</body>
</html>
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