df969706f4
This is the style used in wayland.xml which is the only file we really care about for git blame information. So let's adjust all others to that style for consistency and fix editorconfig to avoid messing this up in the future. Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
129 lines
4.6 KiB
XML
129 lines
4.6 KiB
XML
<?xml version='1.0' encoding='utf-8' ?>
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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % BOOK_ENTITIES SYSTEM "Wayland.ent">
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%BOOK_ENTITIES;
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]>
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<chapter id="chap-Compositors">
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<title>Types of Compositors</title>
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<para>
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Compositors come in different types, depending on which
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role they play in the overall architecture of the OS.
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For instance, a
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<link linkend="sect-Compositors-System-Compositor">system compositor</link>
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can be used for booting the system, handling multiple user switching, a
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possible console terminal emulator and so forth. A different compositor, a
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<link linkend="sect-Compositors-Session-Compositor">session compositor</link>
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would provide the actual desktop environment. There are many ways for
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different types of compositors to co-exist.
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</para>
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<para>
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In this section, we introduce three types of Wayland compositors relying
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on <link linkend="sect-Library-Server">libwayland-server</link>.
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</para>
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<section id="sect-Compositors-System-Compositor">
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<title>System Compositor</title>
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<para>
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A system compositor can run from early boot until shutdown.
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It effectively replaces the kernel vt system, and can tie in
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with the systems graphical boot setup and multiseat support.
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</para>
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<para>
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A system compositor can host different types of session
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compositors, and let us switch between multiple sessions
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(fast user switching, or secure/personal desktop switching).
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</para>
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<para>
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A linux implementation of a system compositor will typically
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use libudev, egl, kms, evdev and cairo.
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</para>
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<para>
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For fullscreen clients, the system compositor can reprogram the
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video scanout address to read directly from the client provided
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buffer.
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</para>
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</section>
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<section id="sect-Compositors-Session-Compositor">
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<title>Session Compositor</title>
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<para>
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A session compositor is responsible for a single user session.
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If a system compositor is present, the session compositor will
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run nested under the system compositor. Nesting is feasible because
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the protocol is asynchronous; roundtrips would be too expensive
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when nesting is involved. If no system compositor is present, a
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session compositor can run directly on the hardware.
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</para>
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<para>
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X applications can continue working under a session compositor
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by means of a root-less X server that is activated on demand.
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</para>
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<para>
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Possible examples for session compositors include
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<itemizedlist>
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<listitem>
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<para>
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gnome-shell
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</para>
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</listitem>
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<listitem>
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<para>
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moblin
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</para>
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</listitem>
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<listitem>
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<para>
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kwin
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</para>
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</listitem>
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<listitem>
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<para>
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kmscon
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</para>
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</listitem>
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<listitem>
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<para>
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rdp session
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</para>
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</listitem>
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<listitem>
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<para>
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Weston with X11 or Wayland backend is a session compositor nested
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in another session compositor.
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</para>
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</listitem>
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<listitem>
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<para>
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fullscreen X session under Wayland
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</section>
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<section id="sect-Compositors-Embedding-Compositor">
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<title>Embedding Compositor</title>
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<para>
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X11 lets clients embed windows from other clients, or lets clients
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copy pixmap contents rendered by another client into their window.
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This is often used for applets in a panel, browser plugins and similar.
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Wayland doesn't directly allow this, but clients can communicate GEM
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buffer names out-of-band, for example, using D-Bus, or command line
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arguments when the panel launches the applet. Another option is to
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use a nested Wayland instance. For this, the Wayland server will have
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to be a library that the host application links to. The host
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application will then pass the Wayland server socket name to the
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embedded application, and will need to implement the Wayland
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compositor interface. The host application composites the client
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surfaces as part of it's window, that is, in the web page or in the
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panel. The benefit of nesting the Wayland server is that it provides
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the requests the embedded client needs to inform the host about buffer
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updates and a mechanism for forwarding input events from the host
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application.
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</para>
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<para>
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An example for this kind of setup is firefox embedding the flash
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player as a kind of special-purpose compositor.
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</para>
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</section>
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</chapter>
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