1 <!DOCTYPE HTML PUBLIC
"-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
4 <meta http-equiv=
"content-type" content=
"text/html; charset=utf-8">
5 <title>Mesa EGL
</title>
6 <link rel=
"stylesheet" type=
"text/css" href=
"mesa.css">
11 <h1>The Mesa
3D Graphics Library
</h1>
14 <iframe src=
"contents.html"></iframe>
19 <p>The current version of EGL in Mesa implements EGL
1.4. More information
20 about EGL can be found at
21 <a href=
"http://www.khronos.org/egl/">
22 http://www.khronos.org/egl/
</a>.
</p>
24 <p>The Mesa's implementation of EGL uses a driver architecture. The main
25 library (
<code>libEGL
</code>) is window system neutral. It provides the EGL
26 API entry points and helper functions for use by the drivers. Drivers are
27 dynamically loaded by the main library and most of the EGL API calls are
28 directly dispatched to the drivers.
</p>
30 <p>The driver in use decides the window system to support.
</p>
36 <p>Run
<code>configure
</code> with the desired client APIs and enable
37 the driver for your hardware. For example
</p>
40 $ ./configure --enable-gles1 --enable-gles2 \
41 --with-dri-drivers=... \
42 --with-gallium-drivers=...
45 <p>The main library and OpenGL is enabled by default. The first two options
46 above enables
<a href=
"opengles.html">OpenGL ES
1.x and
2.x
</a>. The last two
47 options enables the listed classic and and Gallium drivers respectively.
</p>
51 <li>Build and install Mesa as usual.
</li>
54 <p>In the given example, it will build and install
<code>libEGL
</code>,
55 <code>libGL
</code>,
<code>libGLESv1_CM
</code>,
<code>libGLESv2
</code>, and one
56 or more EGL drivers.
</p>
58 <h3>Configure Options
</h3>
60 <p>There are several options that control the build of EGL at configuration
64 <dt><code>--enable-egl
</code></dt>
67 <p>By default, EGL is enabled. When disabled, the main library and the drivers
68 will not be built.
</p>
72 <dt><code>--with-egl-driver-dir
</code></dt>
75 <p>The directory EGL drivers should be installed to. If not specified, EGL
76 drivers will be installed to
<code>${libdir}/egl
</code>.
</p>
80 <dt><code>--with-egl-platforms
</code></dt>
83 <p>List the platforms (window systems) to support. Its argument is a comma
84 separated string such as
<code>--with-egl-platforms=x11,drm
</code>. It decides
85 the platforms a driver may support. The first listed platform is also used by
86 the main library to decide the native platform: the platform the EGL native
87 types such as
<code>EGLNativeDisplayType
</code> or
88 <code>EGLNativeWindowType
</code> defined for.
</p>
90 <p>The available platforms are
<code>x11
</code>,
<code>drm
</code>,
91 <code>wayland
</code>,
<code>null
</code>,
<code>android
</code>,
92 <code>haiku
</code>, and
<code>gdi
</code>. The
<code>android
</code> platform
93 can only be built as a system component, part of AOSP, while the
94 <code>haiku
</code> and
<code>gdi
</code> platforms can only be built with SCons.
95 Unless for special needs, the build system should
96 select the right platforms automatically.
</p>
100 <dt><code>--enable-gles1
</code></dt>
101 <dt><code>--enable-gles2
</code></dt>
104 <p>These options enable OpenGL ES support in OpenGL. The result is one big
105 internal library that supports multiple APIs.
</p>
109 <dt><code>--enable-shared-glapi
</code></dt>
112 <p>By default,
<code>libGL
</code> has its own copy of
<code>libglapi
</code>.
113 This options makes
<code>libGL
</code> use the shared
<code>libglapi
</code>. This
114 is required if applications mix OpenGL and OpenGL ES.
</p>
124 <p>There are demos for the client APIs supported by EGL. They can be found in
125 mesa/demos repository.
</p>
127 <h3>Environment Variables
</h3>
129 <p>There are several environment variables that control the behavior of EGL at
133 <dt><code>EGL_DRIVERS_PATH
</code></dt>
136 <p>By default, the main library will look for drivers in the directory where
137 the drivers are installed to. This variable specifies a list of
138 colon-separated directories where the main library will look for drivers, in
139 addition to the default directory. This variable is ignored for setuid/setgid
142 <p>This variable is usually set to test an uninstalled build. For example, one
146 $ export LD_LIBRARY_PATH=$mesa/lib
147 $ export EGL_DRIVERS_PATH=$mesa/lib/egl
150 <p>to test a build without installation
</p>
154 <dt><code>EGL_DRIVER
</code></dt>
157 <p>This variable specifies a full path to or the name of an EGL driver. It
158 forces the specified EGL driver to be loaded. It comes in handy when one wants
159 to test a specific driver. This variable is ignored for setuid/setgid
164 <dt><code>EGL_PLATFORM
</code></dt>
167 <p>This variable specifies the native platform. The valid values are the same
168 as those for
<code>--with-egl-platforms
</code>. When the variable is not set,
169 the main library uses the first platform listed in
170 <code>--with-egl-platforms
</code> as the native platform.
</p>
172 <p>Extensions like
<code>EGL_MESA_drm_display
</code> define new functions to
173 create displays for non-native platforms. These extensions are usually used by
174 applications that support non-native platforms. Setting this variable is
175 probably required only for some of the demos found in mesa/demo repository.
</p>
179 <dt><code>EGL_LOG_LEVEL
</code></dt>
182 <p>This changes the log level of the main library and the drivers. The valid
183 values are:
<code>debug
</code>,
<code>info
</code>,
<code>warning
</code>, and
184 <code>fatal
</code>.
</p>
188 <dt><code>EGL_SOFTWARE
</code></dt>
191 <p>For drivers that support both hardware and software rendering, setting this
192 variable to true forces the use of software rendering.
</p>
200 <dt><code>egl_dri2
</code></dt>
203 <p>This driver supports both
<code>x11
</code> and
<code>drm
</code> platforms.
204 It functions as a DRI driver loader. For
<code>x11
</code> support, it talks to
205 the X server directly using (XCB-)DRI2 protocol.
</p>
207 <p>This driver can share DRI drivers with
<code>libGL
</code>.
</p>
213 <p>The ABI between the main library and its drivers are not stable. Nor is
214 there a plan to stabilize it at the moment.
</p>
218 <p>The sources of the main library and drivers can be found at
219 <code>src/egl/
</code>.
</p>
221 <h3>Lifetime of Display Resources
</h3>
223 <p>Contexts and surfaces are examples of display resources. They might live
224 longer than the display that creates them.
</p>
226 <p>In EGL, when a display is terminated through
<code>eglTerminate
</code>, all
227 display resources should be destroyed. Similarly, when a thread is released
228 through
<code>eglReleaseThread
</code>, all current display resources should be
229 released. Another way to destroy or release resources is through functions
230 such as
<code>eglDestroySurface
</code> or
<code>eglMakeCurrent
</code>.
</p>
232 <p>When a resource that is current to some thread is destroyed, the resource
233 should not be destroyed immediately. EGL requires the resource to live until
234 it is no longer current. A driver usually calls
235 <code>eglIs
<Resource
>Bound
</code> to check if a resource is bound
236 (current) to any thread in the destroy callbacks. If it is still bound, the
237 resource is not destroyed.
</p>
239 <p>The main library will mark destroyed current resources as unlinked. In a
240 driver's
<code>MakeCurrent
</code> callback,
241 <code>eglIs
<Resource
>Linked
</code> can then be called to check if a newly
242 released resource is linked to a display. If it is not, the last reference to
243 the resource is removed and the driver should destroy the resource. But it
244 should be careful here because
<code>MakeCurrent
</code> might be called with an
245 uninitialized display.
</p>
247 <p>This is the only mechanism provided by the main library to help manage the
248 resources. The drivers are responsible to the correct behavior as defined by
251 <h3><code>EGL_RENDER_BUFFER
</code></h3>
253 <p>In EGL, the color buffer a context should try to render to is decided by the
254 binding surface. It should try to render to the front buffer if the binding
255 surface has
<code>EGL_RENDER_BUFFER
</code> set to
256 <code>EGL_SINGLE_BUFFER
</code>; If the same context is later bound to a
257 surface with
<code>EGL_RENDER_BUFFER
</code> set to
258 <code>EGL_BACK_BUFFER
</code>, the context should try to render to the back
259 buffer. However, the context is allowed to make the final decision as to which
260 color buffer it wants to or is able to render to.
</p>
262 <p>For pbuffer surfaces, the render buffer is always
263 <code>EGL_BACK_BUFFER
</code>. And for pixmap surfaces, the render buffer is
264 always
<code>EGL_SINGLE_BUFFER
</code>. Unlike window surfaces, EGL spec
265 requires their
<code>EGL_RENDER_BUFFER
</code> values to be honored. As a
266 result, a driver should never set
<code>EGL_PIXMAP_BIT
</code> or
267 <code>EGL_PBUFFER_BIT
</code> bits of a config if the contexts created with the
268 config won't be able to honor the
<code>EGL_RENDER_BUFFER
</code> of pixmap or
269 pbuffer surfaces.
</p>
271 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
272 single-buffered, in that
<code>eglSwapBuffers
</code> has no effect on them. It
273 is desirable that a driver allocates a private color buffer for each pbuffer
274 surface created. If the window system the driver supports has native pbuffers,
275 or if the native pixmaps have more than one color buffers, the driver should
276 carefully attach the native color buffers to the EGL surfaces, re-route them if
279 <p>There is no defined behavior as to, for example, how
280 <code>glDrawBuffer
</code> interacts with
<code>EGL_RENDER_BUFFER
</code>. Right
281 now, it is desired that the draw buffer in a client API be fixed for pixmap and
282 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
283 client API renders to the specified render buffer for pixmap and pbuffer
286 <h3><code>EGLDisplay
</code> Mutex
</h3>
288 The
<code>EGLDisplay
</code> will be locked before calling any of the dispatch
289 functions (well, except for GetProcAddress which does not take an
290 <code>EGLDisplay
</code>). This guarantees that the same dispatch function will
291 not be called with the sample display at the same time. If a driver has access
292 to an
<code>EGLDisplay
</code> without going through the EGL APIs, the driver
293 should as well lock the display before using it.