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.
</p>
28 <p>Run
<code>configure
</code> with the desired client APIs and enable
29 the driver for your hardware. For example
</p>
32 $ ./configure --enable-gles2 --enable-openvg --enable-gallium-nouveau
35 <p>The main library and OpenGL is enabled by default. The first option above
36 enables
<a href=
"opengles.html">OpenGL ES
2.x
</a>. The second option enables
37 <a href=
"openvg.html">OpenVG
</a>.
</p>
41 <li>Build and install Mesa as usual.
</li>
44 <p>In the given example, it will build and install
<code>libEGL
</code>,
45 <code>libGL
</code>,
<code>libGLESv1_CM
</code>,
<code>libGLESv2
</code>,
46 <code>libOpenVG
</code>, and one or more EGL drivers.
</p>
48 <h3>Configure Options
</h3>
50 <p>There are several options that control the build of EGL at configuration
54 <li><code>--enable-egl
</code>
56 <p>By default, EGL is enabled. When disabled, the main library and the drivers
57 will not be built.
</p>
61 <li><code>--with-egl-driver-dir
</code>
63 <p>The directory EGL drivers should be installed to. If not specified, EGL
64 drivers will be installed to
<code>${libdir}/egl
</code>.
</p>
68 <li><code>--with-egl-platforms
</code>
70 <p>List the platforms (window systems) to support. Its argument is a comma
71 seprated string such as
<code>--with-egl-platforms=x11,drm
</code>. It decides
72 the platforms a driver may support. The first listed platform is also used by
73 the main library to decide the native platform: the platform the EGL native
74 types such as
<code>EGLNativeDisplayType
</code> or
75 <code>EGLNativeWindowType
</code> defined for.
</p>
77 <p>The available platforms are
<code>x11
</code>,
<code>drm
</code>,
78 <code>fbdev
</code>, and
<code>gdi
</code>. The
<code>gdi
</code> platform can
79 only be built with SCons. Unless for special needs, the build system should
80 select the right platforms automatically.
</p>
84 <li><code>--enable-gles1
</code> and
<code>--enable-gles2
</code>
86 <p>These options enable OpenGL ES support in OpenGL. The result is one big
87 internal library that supports multiple APIs.
</p>
91 <li><code>--enable-gles-overlay
</code>
93 <p>This option enables OpenGL ES as separate internal libraries. This is an
94 alternative approach to enable OpenGL ES.
</p>
96 <p>This is only supported by
<code>egl_gallium
</code>. For systems using DRI
97 drivers,
<code>--enable-gles1
</code> and
<code>--enable-gles2
</code> are
98 suggested instead as all drivers will benefit.
</p>
102 <li><code>--enable-openvg
</code>
104 <p>OpenVG must be explicitly enabled by this option.
</p>
108 <li><code>--enable-gallium-egl
</code>
110 <p>Explicitly enable or disable
<code>egl_gallium
</code>.
</p>
120 <p>There are demos for the client APIs supported by EGL. They can be found in
121 mesa/demos repository.
</p>
123 <h3>Environment Variables
</h3>
125 <p>There are several environment variables that control the behavior of EGL at
129 <li><code>EGL_DRIVERS_PATH
</code>
131 <p>By default, the main library will look for drivers in the directory where
132 the drivers are installed to. This variable specifies a list of
133 colon-separated directories where the main library will look for drivers, in
134 addition to the default directory. This variable is ignored for setuid/setgid
139 <li><code>EGL_DRIVER
</code>
141 <p>This variable specifies a full path to an EGL driver and it forces the
142 specified EGL driver to be loaded. It comes in handy when one wants to test a
143 specific driver. This variable is ignored for setuid/setgid binaries.
</p>
147 <li><code>EGL_PLATFORM
</code>
149 <p>This variable specifies the native platform. The valid values are the same
150 as those for
<code>--with-egl-platforms
</code>. When the variable is not set,
151 the main library uses the first platform listed in
152 <code>--with-egl-platforms
</code> as the native platform.
</p>
154 <p>Extensions like
<code>EGL_MESA_drm_display
</code> define new functions to
155 create displays for non-native platforms. These extensions are usually used by
156 applications that support non-native platforms. Setting this variable is
157 probably required only for some of the demos found in mesa/demo repository.
</p>
161 <li><code>EGL_LOG_LEVEL
</code>
163 <p>This changes the log level of the main library and the drivers. The valid
164 values are:
<code>debug
</code>,
<code>info
</code>,
<code>warning
</code>, and
165 <code>fatal
</code>.
</p>
169 <li><code>EGL_SOFTWARE
</code>
171 <p>For drivers that support both hardware and software rendering, setting this
172 variable to true forces the use of software rendering.
</p>
180 <li><code>egl_dri2
</code>
182 <p>This driver supports both
<code>x11
</code> and
<code>drm
</code> platforms.
183 It functions as a DRI driver loader. For
<code>x11
</code> support, it talks to
184 the X server directly using (XCB-)DRI2 protocol.
</p>
186 <p>This driver can share DRI drivers with
<code>libGL
</code>.
</p>
190 <li><code>egl_gallium
</code>
192 <p>This driver is based on Gallium3D. It supports all rendering APIs and
193 hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
194 The supported platforms are X11, DRM, FBDEV, and GDI.
</p>
196 <p>This driver comes with its own hardware drivers
197 (
<code>pipe_
<hw
></code>) and client API modules
198 (
<code>st_
<api
></code>).
</p>
202 <li><code>egl_glx
</code>
204 <p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
205 the EGL API. It supports both direct and indirect rendering when the GLX does.
206 It is accelerated when the GLX is. As such, it cannot provide functions that
207 is not available in GLX or GLX extensions.
</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. Of the EGL drivers,
215 <code>egl_gallium
</code> has its own hardware drivers and client API modules.
216 They are considered internal to
<code>egl_gallium
</code> and there is also no
217 stable ABI between them. These should be kept in mind when packaging for
220 <p>Generally,
<code>egl_dri2
</code> is preferred over
<code>egl_gallium
</code>
221 when the system already has DRI drivers. As
<code>egl_gallium
</code> is loaded
222 before
<code>egl_dri2
</code> when both are available,
<code>egl_gallium
</code>
223 may either be disabled with
<code>--disable-gallium-egl
</code> or packaged
228 <p>The sources of the main library and the classic drivers can be found at
229 <code>src/egl/
</code>. The sources of the
<code>egl
</code> state tracker can
230 be found at
<code>src/gallium/state_trackers/egl/
</code>.
</p>
232 <p>The suggested way to learn to write a EGL driver is to see how other drivers
233 are written.
<code>egl_glx
</code> should be a good reference. It works in any
234 environment that has GLX support, and it is simpler than most drivers.
</p>
236 <h3>Lifetime of Display Resources
</h3>
238 <p>Contexts and surfaces are examples of display resources. They might live
239 longer than the display that creates them.
</p>
241 <p>In EGL, when a display is terminated through
<code>eglTerminate
</code>, all
242 display resources should be destroyed. Similarly, when a thread is released
243 throught
<code>eglReleaseThread
</code>, all current display resources should be
244 released. Another way to destory or release resources is through functions
245 such as
<code>eglDestroySurface
</code> or
<code>eglMakeCurrent
</code>.
</p>
247 <p>When a resource that is current to some thread is destroyed, the resource
248 should not be destroyed immediately. EGL requires the resource to live until
249 it is no longer current. A driver usually calls
250 <code>eglIs
<Resource
>Bound
</code> to check if a resource is bound
251 (current) to any thread in the destroy callbacks. If it is still bound, the
252 resource is not destroyed.
</p>
254 <p>The main library will mark destroyed current resources as unlinked. In a
255 driver's
<code>MakeCurrent
</code> callback,
256 <code>eglIs
<Resource
>Linked
</code> can then be called to check if a newly
257 released resource is linked to a display. If it is not, the last reference to
258 the resource is removed and the driver should destroy the resource. But it
259 should be careful here because
<code>MakeCurrent
</code> might be called with an
260 uninitialized display.
</p>
262 <p>This is the only mechanism provided by the main library to help manage the
263 resources. The drivers are responsible to the correct behavior as defined by
266 <h3><code>EGL_RENDER_BUFFER
</code></h3>
268 <p>In EGL, the color buffer a context should try to render to is decided by the
269 binding surface. It should try to render to the front buffer if the binding
270 surface has
<code>EGL_RENDER_BUFFER
</code> set to
271 <code>EGL_SINGLE_BUFFER
</code>; If the same context is later bound to a
272 surface with
<code>EGL_RENDER_BUFFER
</code> set to
273 <code>EGL_BACK_BUFFER
</code>, the context should try to render to the back
274 buffer. However, the context is allowed to make the final decision as to which
275 color buffer it wants to or is able to render to.
</p>
277 <p>For pbuffer surfaces, the render buffer is always
278 <code>EGL_BACK_BUFFER
</code>. And for pixmap surfaces, the render buffer is
279 always
<code>EGL_SINGLE_BUFFER
</code>. Unlike window surfaces, EGL spec
280 requires their
<code>EGL_RENDER_BUFFER
</code> values to be honored. As a
281 result, a driver should never set
<code>EGL_PIXMAP_BIT
</code> or
282 <code>EGL_PBUFFER_BIT
</code> bits of a config if the contexts created with the
283 config won't be able to honor the
<code>EGL_RENDER_BUFFER
</code> of pixmap or
284 pbuffer surfaces.
</p>
286 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
287 single-buffered, in that
<code>eglSwapBuffers
</code> has no effect on them. It
288 is desirable that a driver allocates a private color buffer for each pbuffer
289 surface created. If the window system the driver supports has native pbuffers,
290 or if the native pixmaps have more than one color buffers, the driver should
291 carefully attach the native color buffers to the EGL surfaces, re-route them if
294 <p>There is no defined behavior as to, for example, how
295 <code>glDrawBuffer
</code> interacts with
<code>EGL_RENDER_BUFFER
</code>. Right
296 now, it is desired that the draw buffer in a client API be fixed for pixmap and
297 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
298 client API renders to the specified render buffer for pixmap and pbuffer
301 <h3><code>EGLDisplay
</code> Mutex
</h3>
303 The
<code>EGLDisplay
</code> will be locked before calling any of the dispatch
304 functions (well, except for GetProcAddress which does not take an
305 <code>EGLDisplay
</code>). This guarantees that the same dispatch function will
306 not be called with the sample display at the same time. If a driver has access
307 to an
<code>EGLDisplay
</code> without going through the EGL APIs, the driver
308 should as well lock the display before using it.
313 <li>Pass the conformance tests
</li>
314 <li>Mixed use of OpenGL, OpenGL ES
1.1, and OpenGL ES
2.0 is supported. But
315 which one of
<code>libGL.so
</code>,
<code>libGLESv1_CM.so
</code>, and
316 <code>libGLESv2.so
</code> should an application link to? Bad things may happen
317 when, say, an application is linked to
<code>libGLESv2.so
</code> and
318 <code>libcairo
</code>, which is linked to
<code>libGL.so
</code> instead.
</li>