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<html>
<title>Mesa EGL</title>
<head><link rel="stylesheet" type="text/css" href="mesa.css"></head>
<body>
<h1>Mesa EGL</h1>
<p>The current version of EGL in Mesa implements EGL 1.4. More information
about EGL can be found at
<a href="http://www.khronos.org/egl/" target="_parent">
http://www.khronos.org/egl/</a>.</p>
<p>The Mesa's implementation of EGL uses a driver architecture. The main
library (<code>libEGL</code>) is window system neutral. It provides the EGL
API entry points and helper functions for use by the drivers. Drivers are
dynamically loaded by the main library and most of the EGL API calls are
directly dispatched to the drivers.</p>
<p>The driver in use decides the window system to support. For drivers that
support hardware rendering, there are usually multiple drivers supporting the
same window system. Each one of of them supports a certain range of graphics
cards.</p>
<h2>Build EGL</h2>
<ol>
<li>
<p>Run <code>configure</code> with the desired state trackers and and enable
the Gallium driver for your hardware. For example</p>
<pre>
$ ./configure --with-state-trackers=egl_g3d,es,vega --enable-gallium-intel
</pre>
<p>The main library will be enabled by default. The <code>egl_g3d</code> state
tracker is needed by a number of EGL drivers. EGL drivers will be covered
later. The <a href="opengles.html">es state tracker</a> provides OpenGL ES 1.x
and 2.x and the <a href="openvg.html">vega state tracker</a> provides OpenVG
1.x.</p>
</li>
<li>Build and install Mesa as usual.</li>
</ol>
<p>In the given example, it will build and install <code>libEGL</code>,
<code>libGLESv1_CM</code>, <code>libGLESv2</code>, <code>libOpenVG</code>, and
one or more EGL drivers.</p>
<h3>Configure Options</h3>
<p>There are several options that control the build of EGL at configuration
time</p>
<ul>
<li><code>--enable-egl</code>
<p>By default, EGL is enabled. When disabled, the main library and the drivers
will not be built.</p>
</li>
<li><code>--with-egl-displays</code>
<p>List the window system(s) to support. It is by default <code>x11</code>,
which supports the X Window System. Its argument is a comma separated string
like, for example, <code>--with-egl-displays=x11,kms</code>. Because an EGL
driver decides which window system to support, this example will enable two
(sets of) EGL drivers. One supports the X window system and the other supports
bare KMS (kernel modesetting).</p>
</li>
<li><code>--with-state-trackers</code>
<p>The argument is a comma separated string. It is usually used to specify the
rendering APIs, like OpenGL ES or OpenVG, to build. But it should be noted
that a number of EGL drivers depend on the <code>egl_g3d</code> state tracker.
They will <em>not</em> be built without the <code>egl_g3d</code> state
tracker.</p>
</li>
</ul>
<h3>OpenGL</h3>
<p>The OpenGL state tracker is not built in the above example. It should be
noted that the classic <code>libGL</code> is not a state tracker and cannot be
used with EGL (unless the EGL driver in use is <code>egl_glx</code>). To build
the OpenGL state tracker, one may append <code>glx</code> to
<code>--with-state-trackers</code> and manually build
<code>src/gallium/winsys/xlib/</code>.</p>
<h2>Use EGL</h2>
<p> The demos for OpenGL ES and OpenVG can be found in <code>progs/es1/</code>,
<code>progs/es2/</code> and <code>progs/openvg/</code>. You can use them to
test your build. For example,</p>
<pre>
$ cd progs/es1/xegl
$ make
$ ./torus
</pre>
<h3>Environment Variables</h3>
<p>There are several environment variables that control the behavior of EGL at
runtime</p>
<ul>
<li><code>EGL_DRIVER</code>
<p>This variable forces the specified EGL driver to be loaded. It comes in
handy when one wants to test a specific driver.</p>
</li>
<li><code>EGL_DISPLAY</code>
<p>When <code>EGL_DRIVER</code> is not set, the main library loads <em>all</em>
EGL drivers that support a certain window system. <code>EGL_DISPLAY</code> can
be used to specify the window system and the valid values are, for example,
<code>x11</code> or <code>kms</code>. When the variable is not set, the main
library defaults the value to the first window system listed in
<code>--with-egl-displays</code> at configuration time.
</li>
<li><code>EGL_LOG_LEVEL</code>
<p>This changes the log level of the main library and the drivers. The valid
values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
<code>fatal</code>.</p>
</li>
<li><code>EGL_SOFTWARE</code>
<p>For drivers that support both hardware and software rendering, setting this
variable to true forces the use of software rendering.</p>
</li>
</ul>
<h2>EGL Drivers</h2>
<p>There are two categories of EGL drivers: Gallium and classic.</p>
<p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4. The
support for optional EGL functions and EGL extensions is usually more complete
than the classic ones. These drivers depend on the <code>egl_g3d</code> state
tracker to build. The available drivers are</p>
<ul>
<li><code>egl_<dpy>_i915</code></li>
<li><code>egl_<dpy>_i965</code></li>
<li><code>egl_<dpy>_radeon</code></li>
<li><code>egl_<dpy>_nouveau</code></li>
<li><code>egl_<dpy>_vmwgfx</code></li>
</ul>
<p><code><dpy></code> is given by <code>--with-egl-displays</code> at
configuration time. There will be one EGL driver for each combination of the
displays listed and the hardware drivers enabled.</p>
<p>Classic EGL drivers, on the other hand, supports only OpenGL as its
rendering API. They can be found under <code>src/egl/drivers/</code>. There
are 3 of them</p>
<ul>
<li><code>egl_glx</code>
<p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
the EGL API. It supports both direct and indirect rendering when the GLX does.
It is accelerated when the GLX is. As such, it cannot provide functions that
is not available in GLX or GLX extensions.</p>
</li>
<li><code>egl_xdri</code>
<p>This driver supports the X Window System as its window system. It functions
as a DRI driver loader. Unlike <code>egl_glx</code>, it has no dependency on
<code>libGL</code>. It talks to the X server directly using DRI or DRI2
protocols. It also talks minimal GLX protocol for things like available
visuals or fbconfigs. With direct access to the DRI drivers, it has the
potential to support more EGL functions that are not possible with
<code>egl_glx</code></p>
</li>
<li><code>egl_dri</code>
<p>This driver lacks maintenance and does <em>not</em> build. It is similiar
to <code>egl_xdri</code> in that it functions as a DRI driver loader. But
unlike <code>egl_xdri</code>, it supports Linux framebuffer devices as its
window system and supports EGL_MESA_screen_surface extension. It loads only
DRI1 drivers. As DRI1 drivers is phasing out, it might be better to rewrite
the driver to support KMS and DRI2.</p>
</li>
</ul>
<p>To use the classic drivers, one must manually set <code>EGL_DRIVER</code> at
runtime.</p>
<h2>Developers</h2>
The sources of the main library and the classic drivers can be found at
<code>src/egl/</code>. The sources of the <code>egl_g3d</code> state tracker
can be found at <code>src/gallium/state_trackers/egl_g3d/</code>.
<h3>TODOs</h3>
<ul>
<li>Thread safety</li>
<li>Pass the conformance tests</li>
<li>Better automatic driver selection: <code>EGL_DISPLAY</code> loads all
drivers and might eat too much memory.</li>
</ul>
</body>
</html>
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