3 <title>Mesa EGL
</title>
5 <head><link rel=
"stylesheet" type=
"text/css" href=
"mesa.css"></head>
11 <p>The current version of EGL in Mesa implements EGL
1.4. More information
12 about EGL can be found at
13 <a href=
"http://www.khronos.org/egl/" target=
"_parent">
14 http://www.khronos.org/egl/
</a>.
</p>
16 <p>The Mesa's implementation of EGL uses a driver architecture. The main
17 library (
<code>libEGL
</code>) is window system neutral. It provides the EGL
18 API entry points and helper functions for use by the drivers. Drivers are
19 dynamically loaded by the main library and most of the EGL API calls are
20 directly dispatched to the drivers.
</p>
22 <p>The driver in use decides the window system to support. For drivers that
23 support hardware rendering, there are usually multiple drivers supporting the
24 same window system. Each one of of them supports a certain range of graphics
31 <p>Run
<code>configure
</code> with the desired state trackers and enable
32 the Gallium driver for your hardware. For example
</p>
35 $ ./configure --enable-gles-overlay --with-state-trackers=egl,vega --enable-gallium-{swrast,intel}
38 <p>The main library and OpenGL is enabled by default. The first option enables
39 <a href=
"opengles.html">OpenGL ES
1.x and
2.x
</a>. The
<code>egl
</code> state
40 tracker is needed by a number of EGL drivers. EGL drivers will be covered
41 later. The
<a href=
"openvg.html">vega state tracker
</a> provides OpenVG
45 <li>Build and install Mesa as usual.
</li>
48 <p>In the given example, it will build and install
<code>libEGL
</code>,
49 <code>libGL
</code>,
<code>libGLESv1_CM
</code>,
<code>libGLESv2
</code>,
50 <code>libOpenVG
</code>, and one or more EGL drivers.
</p>
52 <h3>Configure Options
</h3>
54 <p>There are several options that control the build of EGL at configuration
58 <li><code>--enable-egl
</code>
60 <p>By default, EGL is enabled. When disabled, the main library and the drivers
61 will not be built.
</p>
65 <li><code>--with-egl-driver-dir
</code>
67 <p>The directory EGL drivers should be installed to. If not specified, EGL
68 drivers will be installed to
<code>${libdir}/egl
</code>.
</p>
72 <li><code>--with-egl-displays
</code>
74 <p>List the window system(s) to support. It is by default
<code>x11
</code>,
75 which supports the X Window System. Its argument is a comma separated string
76 like, for example,
<code>--with-egl-displays=x11,kms
</code>. Because an EGL
77 driver decides which window system to support, this example will enable two
78 (sets of) EGL drivers. One supports the X window system and the other supports
79 bare KMS (kernel modesetting).
</p>
81 <p>The available displays are
<code>x11
</code>,
<code>kms
</code>,
82 <code>fbdev
</code>, and
<code>gdi
</code>. The
<code>gdi
</code> display can
83 only be built with SCons.
</p>
87 <li><code>--with-state-trackers
</code>
89 <p>The argument is a comma separated string. It is usually used to specify the
90 rendering APIs, such as OpenVG, to build. But it should be noted that a number
91 of EGL drivers depend on the
<code>egl
</code> state tracker. They will
92 <em>not
</em> be built without the
<code>egl
</code> state tracker.
</p>
96 <li><code>--enable-gles-overlay
</code>
98 <p>OpenGL and OpenGL ES are not controlled by
99 <code>--with-state-trackers
</code>. OpenGL is always built. To build OpenGL
100 ES, this option must be explicitly given.
</p>
104 <li><code>--enable-gles1
</code> and
<code>--enable-gles2
</code>
106 <p>Unlike
<code>--enable-gles-overlay
</code>, which builds one library for each
107 rendering API, these options enable OpenGL ES support in OpenGL. The result is
108 one big library that supports multiple APIs. This is used by DRI drivers and
109 <code>egl_dri2
</code> EGL driver.
113 <li><code>--enable-gallium-swrast
</code>
115 <p>This option is not specific to EGL. But if there is no driver for your
116 hardware, or you are experiencing problems with the hardware driver, you can
117 enable the swrast DRM driver. It is a dummy driver and EGL will fallback to
118 software rendering automatically.
</p>
127 <p>There are demos for the client APIs supported by EGL. They can be found in
128 mesa/demos repository.
</p>
130 <h3>Environment Variables
</h3>
132 <p>There are several environment variables that control the behavior of EGL at
136 <li><code>EGL_DRIVERS_PATH
</code>
138 <p>By default, the main library will look for drivers in the directory where
139 the drivers are installed to. This variable specifies a list of
140 colon-separated directories where the main library will look for drivers, in
141 addition to the default directory. This variable is ignored for setuid/setgid
146 <li><code>EGL_DRIVER
</code>
148 <p>This variable specifies a full path to an EGL driver and it forces the
149 specified EGL driver to be loaded. It comes in handy when one wants to test a
150 specific driver. This variable is ignored for setuid/setgid binaries.
</p>
154 <li><code>EGL_DISPLAY
</code>
156 <p>When
<code>EGL_DRIVER
</code> is not set, the main library loads
<em>all
</em>
157 EGL drivers that support a certain window system.
<code>EGL_DISPLAY
</code> can
158 be used to specify the window system and the valid values are, for example,
159 <code>x11
</code> or
<code>kms
</code>. When the variable is not set, the main
160 library defaults the value to the first window system listed in
161 <code>--with-egl-displays
</code> at configuration time.
165 <li><code>EGL_LOG_LEVEL
</code>
167 <p>This changes the log level of the main library and the drivers. The valid
168 values are:
<code>debug
</code>,
<code>info
</code>,
<code>warning
</code>, and
169 <code>fatal
</code>.
</p>
173 <li><code>EGL_SOFTWARE
</code>
175 <p>For drivers that support both hardware and software rendering, setting this
176 variable to true forces the use of software rendering.
</p>
183 <p>There are two categories of EGL drivers: Gallium and classic.
</p>
185 <p>Gallium EGL drivers supports all rendering APIs specified in EGL
1.4. These
186 drivers depend on the
<code>egl
</code> state tracker to build. The available
190 <li><code>egl_
<dpy
>_i915
</code></li>
191 <li><code>egl_
<dpy
>_i965
</code></li>
192 <li><code>egl_
<dpy
>_nouveau
</code></li>
193 <li><code>egl_
<dpy
>_radeon
</code></li>
194 <li><code>egl_
<dpy
>_swrast
</code></li>
195 <li><code>egl_
<dpy
>_vmwgfx
</code></li>
198 <p><code><dpy
></code> is given by
<code>--with-egl-displays
</code> at
199 configuration time. There is usually one EGL driver for each combination of
200 the displays listed and the pipe drivers enabled. When the display is pure
201 software or pure hardware, non-working combinations will not be built.
</p>
203 <p>Classic EGL drivers, on the other hand, support only a subset of the
204 available rendering APIs. They can be found under
205 <code>src/egl/drivers/
</code>. There are
3 of them
</p>
208 <li><code>egl_glx
</code>
210 <p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
211 the EGL API. It supports both direct and indirect rendering when the GLX does.
212 It is accelerated when the GLX is. As such, it cannot provide functions that
213 is not available in GLX or GLX extensions.
</p>
216 <li><code>egl_dri2
</code>
218 <p>This driver supports the X Window System as its window system. It functions
219 as a DRI2 driver loader. Unlike
<code>egl_glx
</code>, it has no dependency on
220 <code>libGL
</code>. It talks to the X server directly using DRI2 protocol.
</p>
223 <li><code>egl_dri
</code>
225 <p>This driver lacks maintenance and does
<em>not
</em> build. It is similiar
226 to
<code>egl_dri2
</code> in that it functions as a DRI(
1) driver loader. But
227 unlike
<code>egl_dri2
</code>, it supports Linux framebuffer devices as its
228 window system and supports EGL_MESA_screen_surface extension. As DRI1 drivers
229 are phasing out, it might eventually be replaced by
<code>egl_dri2
</code>.
</p>
234 <p>To use the classic drivers, one must manually set
<code>EGL_DRIVER
</code> at
239 <p>The sources of the main library and the classic drivers can be found at
240 <code>src/egl/
</code>. The sources of the
<code>egl
</code> state tracker can
241 be found at
<code>src/gallium/state_trackers/egl/
</code>.
</p>
243 <p>The suggested way to learn to write a EGL driver is to see how other drivers
244 are written.
<code>egl_glx
</code> should be a good reference. It works in any
245 environment that has GLX support, and it is simpler than most drivers.
</p>
247 <h3>Lifetime of Display Resources
</h3>
249 <p>Contexts and surfaces are examples of display resources. They might live
250 longer than the display that creates them.
</p>
252 <p>In EGL, when a display is terminated through
<code>eglTerminate
</code>, all
253 display resources should be destroyed. Similarly, when a thread is released
254 throught
<code>eglReleaseThread
</code>, all current display resources should be
255 released. Another way to destory or release resources is through functions
256 such as
<code>eglDestroySurface
</code> or
<code>eglMakeCurrent
</code>.
</p>
258 <p>When a resource that is current to some thread is destroyed, the resource
259 should not be destroyed immediately. EGL requires the resource to live until
260 it is no longer current. A driver usually calls
261 <code>eglIs
<Resource
>Bound
</code> to check if a resource is bound
262 (current) to any thread in the destroy callbacks. If it is still bound, the
263 resource is not destroyed.
</p>
265 <p>The main library will mark destroyed current resources as unlinked. In a
266 driver's
<code>MakeCurrent
</code> callback,
267 <code>eglIs
<Resource
>Linked
</code> can then be called to check if a newly
268 released resource is linked to a display. If it is not, the last reference to
269 the resource is removed and the driver should destroy the resource. But it
270 should be careful here because
<code>MakeCurrent
</code> might be called with an
271 uninitialized display.
</p>
273 <p>This is the only mechanism provided by the main library to help manage the
274 resources. The drivers are responsible to the correct behavior as defined by
277 <h3><code>EGL_RENDER_BUFFER
</code></h3>
279 <p>In EGL, the color buffer a context should try to render to is decided by the
280 binding surface. It should try to render to the front buffer if the binding
281 surface has
<code>EGL_RENDER_BUFFER
</code> set to
282 <code>EGL_SINGLE_BUFFER
</code>; If the same context is later bound to a
283 surface with
<code>EGL_RENDER_BUFFER
</code> set to
284 <code>EGL_BACK_BUFFER
</code>, the context should try to render to the back
285 buffer. However, the context is allowed to make the final decision as to which
286 color buffer it wants to or is able to render to.
</p>
288 <p>For pbuffer surfaces, the render buffer is always
289 <code>EGL_BACK_BUFFER
</code>. And for pixmap surfaces, the render buffer is
290 always
<code>EGL_SINGLE_BUFFER
</code>. Unlike window surfaces, EGL spec
291 requires their
<code>EGL_RENDER_BUFFER
</code> values to be honored. As a
292 result, a driver should never set
<code>EGL_PIXMAP_BIT
</code> or
293 <code>EGL_PBUFFER_BIT
</code> bits of a config if the contexts created with the
294 config won't be able to honor the
<code>EGL_RENDER_BUFFER
</code> of pixmap or
295 pbuffer surfaces.
</p>
297 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
298 single-buffered, in that
<code>eglSwapBuffers
</code> has no effect on them. It
299 is desirable that a driver allocates a private color buffer for each pbuffer
300 surface created. If the window system the driver supports has native pbuffers,
301 or if the native pixmaps have more than one color buffers, the driver should
302 carefully attach the native color buffers to the EGL surfaces, re-route them if
305 <p>There is no defined behavior as to, for example, how
306 <code>glDrawBuffer
</code> interacts with
<code>EGL_RENDER_BUFFER
</code>. Right
307 now, it is desired that the draw buffer in a client API be fixed for pixmap and
308 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
309 client API renders to the specified render buffer for pixmap and pbuffer
312 <h3><code>EGLDisplay
</code> Mutex
</h3>
314 The
<code>EGLDisplay
</code> will be locked before calling any of the dispatch
315 functions (well, except for GetProcAddress which does not take an
316 <code>EGLDisplay
</code>). This guarantees that the same dispatch function will
317 not be called with the sample display at the same time. If a driver has access
318 to an
<code>EGLDisplay
</code> without going through the EGL APIs, the driver
319 should as well lock the display before using it.
324 <li>Pass the conformance tests
</li>
325 <li>Better automatic driver selection:
<code>EGL_DISPLAY
</code> loads all
326 drivers and might eat too much memory.
</li>