346 lines
12 KiB
HTML
346 lines
12 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html lang="en">
|
|
<head>
|
|
<meta http-equiv="content-type" content="text/html; charset=utf-8">
|
|
<title>Mesa EGL</title>
|
|
<link rel="stylesheet" type="text/css" href="mesa.css">
|
|
</head>
|
|
<body>
|
|
|
|
<div class="header">
|
|
<h1>The Mesa 3D Graphics Library</h1>
|
|
</div>
|
|
|
|
<iframe src="contents.html"></iframe>
|
|
<div class="content">
|
|
|
|
<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/">
|
|
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.</p>
|
|
|
|
<h2>Build EGL</h2>
|
|
|
|
<ol>
|
|
<li>
|
|
<p>Run <code>configure</code> with the desired client APIs and enable
|
|
the driver for your hardware. For example</p>
|
|
|
|
<pre>
|
|
$ ./configure --enable-gles1 --enable-gles2 \
|
|
--with-dri-drivers=... \
|
|
--with-gallium-drivers=...
|
|
</pre>
|
|
|
|
<p>The main library and OpenGL is enabled by default. The first two options
|
|
above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>. The last two
|
|
options enables the listed classic and and Gallium drivers respectively.</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>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</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>
|
|
|
|
<dl>
|
|
<dt><code>--enable-egl</code></dt>
|
|
<dd>
|
|
|
|
<p>By default, EGL is enabled. When disabled, the main library and the drivers
|
|
will not be built.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>--with-egl-driver-dir</code></dt>
|
|
<dd>
|
|
|
|
<p>The directory EGL drivers should be installed to. If not specified, EGL
|
|
drivers will be installed to <code>${libdir}/egl</code>.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>--enable-gallium-egl</code></dt>
|
|
<dd>
|
|
|
|
<p>Enable the optional <code>egl_gallium</code> driver.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>--with-egl-platforms</code></dt>
|
|
<dd>
|
|
|
|
<p>List the platforms (window systems) to support. Its argument is a comma
|
|
seprated string such as <code>--with-egl-platforms=x11,drm</code>. It decides
|
|
the platforms a driver may support. The first listed platform is also used by
|
|
the main library to decide the native platform: the platform the EGL native
|
|
types such as <code>EGLNativeDisplayType</code> or
|
|
<code>EGLNativeWindowType</code> defined for.</p>
|
|
|
|
<p>The available platforms are <code>x11</code>, <code>drm</code>,
|
|
<code>fbdev</code>, and <code>gdi</code>. The <code>gdi</code> platform can
|
|
only be built with SCons. Unless for special needs, the build system should
|
|
select the right platforms automatically.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>--enable-gles1</code></dt>
|
|
<dt><code>--enable-gles2</code></dt>
|
|
<dd>
|
|
|
|
<p>These options enable OpenGL ES support in OpenGL. The result is one big
|
|
internal library that supports multiple APIs.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>--enable-shared-glapi</code></dt>
|
|
<dd>
|
|
|
|
<p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
|
|
This options makes <code>libGL</code> use the shared <code>libglapi</code>. This
|
|
is required if applications mix OpenGL and OpenGL ES.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>--enable-openvg</code></dt>
|
|
<dd>
|
|
|
|
<p>OpenVG must be explicitly enabled by this option.</p>
|
|
|
|
</dd>
|
|
|
|
</dl>
|
|
|
|
<h2>Use EGL</h2>
|
|
|
|
<h3>Demos</h3>
|
|
|
|
<p>There are demos for the client APIs supported by EGL. They can be found in
|
|
mesa/demos repository.</p>
|
|
|
|
<h3>Environment Variables</h3>
|
|
|
|
<p>There are several environment variables that control the behavior of EGL at
|
|
runtime</p>
|
|
|
|
<dl>
|
|
<dt><code>EGL_DRIVERS_PATH</code></dt>
|
|
<dd>
|
|
|
|
<p>By default, the main library will look for drivers in the directory where
|
|
the drivers are installed to. This variable specifies a list of
|
|
colon-separated directories where the main library will look for drivers, in
|
|
addition to the default directory. This variable is ignored for setuid/setgid
|
|
binaries.</p>
|
|
|
|
<p>This variable is usually set to test an uninstalled build. For example, one
|
|
may set</p>
|
|
|
|
<pre>
|
|
$ export LD_LIBRARY_PATH=$mesa/lib
|
|
$ export EGL_DRIVERS_PATH=$mesa/lib/egl
|
|
</pre>
|
|
|
|
<p>to test a build without installation</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>EGL_DRIVER</code></dt>
|
|
<dd>
|
|
|
|
<p>This variable specifies a full path to or the name of an EGL driver. It
|
|
forces the specified EGL driver to be loaded. It comes in handy when one wants
|
|
to test a specific driver. This variable is ignored for setuid/setgid
|
|
binaries.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>EGL_PLATFORM</code></dt>
|
|
<dd>
|
|
|
|
<p>This variable specifies the native platform. The valid values are the same
|
|
as those for <code>--with-egl-platforms</code>. When the variable is not set,
|
|
the main library uses the first platform listed in
|
|
<code>--with-egl-platforms</code> as the native platform.</p>
|
|
|
|
<p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
|
|
create displays for non-native platforms. These extensions are usually used by
|
|
applications that support non-native platforms. Setting this variable is
|
|
probably required only for some of the demos found in mesa/demo repository.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>EGL_LOG_LEVEL</code></dt>
|
|
<dd>
|
|
|
|
<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>
|
|
|
|
</dd>
|
|
|
|
<dt><code>EGL_SOFTWARE</code></dt>
|
|
<dd>
|
|
|
|
<p>For drivers that support both hardware and software rendering, setting this
|
|
variable to true forces the use of software rendering.</p>
|
|
|
|
</dd>
|
|
</dl>
|
|
|
|
<h2>EGL Drivers</h2>
|
|
|
|
<dl>
|
|
<dt><code>egl_dri2</code></dt>
|
|
<dd>
|
|
|
|
<p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
|
|
It functions as a DRI driver loader. For <code>x11</code> support, it talks to
|
|
the X server directly using (XCB-)DRI2 protocol.</p>
|
|
|
|
<p>This driver can share DRI drivers with <code>libGL</code>.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>egl_gallium</code></dt>
|
|
<dd>
|
|
|
|
<p>This driver is based on Gallium3D. It supports all rendering APIs and
|
|
hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
|
|
The supported platforms are X11, DRM, FBDEV, and GDI.</p>
|
|
|
|
<p>This driver comes with its own hardware drivers
|
|
(<code>pipe_<hw></code>) and client API modules
|
|
(<code>st_<api></code>).</p>
|
|
|
|
</dd>
|
|
|
|
<dt><code>egl_glx</code></dt>
|
|
<dd>
|
|
|
|
<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>
|
|
</dd>
|
|
</dl>
|
|
|
|
<h2>Packaging</h2>
|
|
|
|
<p>The ABI between the main library and its drivers are not stable. Nor is
|
|
there a plan to stabilize it at the moment. Of the EGL drivers,
|
|
<code>egl_gallium</code> has its own hardware drivers and client API modules.
|
|
They are considered internal to <code>egl_gallium</code> and there is also no
|
|
stable ABI between them. These should be kept in mind when packaging for
|
|
distribution.</p>
|
|
|
|
<p>Generally, <code>egl_dri2</code> is preferred over <code>egl_gallium</code>
|
|
when the system already has DRI drivers. As <code>egl_gallium</code> is loaded
|
|
before <code>egl_dri2</code> when both are available, <code>egl_gallium</code>
|
|
is disabled by default.</p>
|
|
|
|
<h2>Developers</h2>
|
|
|
|
<p>The sources of the main library and the classic drivers can be found at
|
|
<code>src/egl/</code>. The sources of the <code>egl</code> state tracker can
|
|
be found at <code>src/gallium/state_trackers/egl/</code>.</p>
|
|
|
|
<p>The suggested way to learn to write a EGL driver is to see how other drivers
|
|
are written. <code>egl_glx</code> should be a good reference. It works in any
|
|
environment that has GLX support, and it is simpler than most drivers.</p>
|
|
|
|
<h3>Lifetime of Display Resources</h3>
|
|
|
|
<p>Contexts and surfaces are examples of display resources. They might live
|
|
longer than the display that creates them.</p>
|
|
|
|
<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
|
|
display resources should be destroyed. Similarly, when a thread is released
|
|
throught <code>eglReleaseThread</code>, all current display resources should be
|
|
released. Another way to destory or release resources is through functions
|
|
such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
|
|
|
|
<p>When a resource that is current to some thread is destroyed, the resource
|
|
should not be destroyed immediately. EGL requires the resource to live until
|
|
it is no longer current. A driver usually calls
|
|
<code>eglIs<Resource>Bound</code> to check if a resource is bound
|
|
(current) to any thread in the destroy callbacks. If it is still bound, the
|
|
resource is not destroyed.</p>
|
|
|
|
<p>The main library will mark destroyed current resources as unlinked. In a
|
|
driver's <code>MakeCurrent</code> callback,
|
|
<code>eglIs<Resource>Linked</code> can then be called to check if a newly
|
|
released resource is linked to a display. If it is not, the last reference to
|
|
the resource is removed and the driver should destroy the resource. But it
|
|
should be careful here because <code>MakeCurrent</code> might be called with an
|
|
uninitialized display.</p>
|
|
|
|
<p>This is the only mechanism provided by the main library to help manage the
|
|
resources. The drivers are responsible to the correct behavior as defined by
|
|
EGL.</p>
|
|
|
|
<h3><code>EGL_RENDER_BUFFER</code></h3>
|
|
|
|
<p>In EGL, the color buffer a context should try to render to is decided by the
|
|
binding surface. It should try to render to the front buffer if the binding
|
|
surface has <code>EGL_RENDER_BUFFER</code> set to
|
|
<code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
|
|
surface with <code>EGL_RENDER_BUFFER</code> set to
|
|
<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
|
|
buffer. However, the context is allowed to make the final decision as to which
|
|
color buffer it wants to or is able to render to.</p>
|
|
|
|
<p>For pbuffer surfaces, the render buffer is always
|
|
<code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
|
|
always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
|
|
requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
|
|
result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
|
|
<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
|
|
config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
|
|
pbuffer surfaces.</p>
|
|
|
|
<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
|
|
single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
|
|
is desirable that a driver allocates a private color buffer for each pbuffer
|
|
surface created. If the window system the driver supports has native pbuffers,
|
|
or if the native pixmaps have more than one color buffers, the driver should
|
|
carefully attach the native color buffers to the EGL surfaces, re-route them if
|
|
required.</p>
|
|
|
|
<p>There is no defined behavior as to, for example, how
|
|
<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
|
|
now, it is desired that the draw buffer in a client API be fixed for pixmap and
|
|
pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
|
|
client API renders to the specified render buffer for pixmap and pbuffer
|
|
surfaces.</p>
|
|
|
|
<h3><code>EGLDisplay</code> Mutex</h3>
|
|
|
|
The <code>EGLDisplay</code> will be locked before calling any of the dispatch
|
|
functions (well, except for GetProcAddress which does not take an
|
|
<code>EGLDisplay</code>). This guarantees that the same dispatch function will
|
|
not be called with the sample display at the same time. If a driver has access
|
|
to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
|
|
should as well lock the display before using it.
|
|
|
|
</div>
|
|
</body>
|
|
</html>
|