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This directory was called Wayland during my early tries with publican where the source layout was different and it needed to be set to the same name as the publican output directory. This reason doesn't exist anymore, so re-name it to publican to make it more obvious what's hiding in here. Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
111 lines
3.8 KiB
XML
111 lines
3.8 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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</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 hw.
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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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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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