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11 <h1>The Mesa 3D Graphics Library</h1>
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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/" target="_parent">
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 <li><code>--enable-egl</code>
66 <p>By default, EGL is enabled. When disabled, the main library and the drivers
67 will not be built.</p>
71 <li><code>--with-egl-driver-dir</code>
73 <p>The directory EGL drivers should be installed to. If not specified, EGL
74 drivers will be installed to <code>${libdir}/egl</code>.</p>
78 <li><code>--enable-gallium-egl</code>
80 <p>Enable the optional <code>egl_gallium</code> driver.</p>
84 <li><code>--with-egl-platforms</code>
86 <p>List the platforms (window systems) to support. Its argument is a comma
87 seprated string such as <code>--with-egl-platforms=x11,drm</code>. It decides
88 the platforms a driver may support. The first listed platform is also used by
89 the main library to decide the native platform: the platform the EGL native
90 types such as <code>EGLNativeDisplayType</code> or
91 <code>EGLNativeWindowType</code> defined for.</p>
93 <p>The available platforms are <code>x11</code>, <code>drm</code>,
94 <code>fbdev</code>, and <code>gdi</code>. The <code>gdi</code> platform can
95 only be built with SCons. Unless for special needs, the build system should
96 select the right platforms automatically.</p>
100 <li><code>--enable-gles1</code> and <code>--enable-gles2</code>
102 <p>These options enable OpenGL ES support in OpenGL. The result is one big
103 internal library that supports multiple APIs.</p>
107 <li><code>--enable-shared-glapi</code>
109 <p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
110 This options makes <code>libGL</code> use the shared <code>libglapi</code>. This
111 is required if applications mix OpenGL and OpenGL ES.</p>
115 <li><code>--enable-openvg</code>
117 <p>OpenVG must be explicitly enabled by this option.</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
144 <p>This variable is usually set to test an uninstalled build. For example, one
148 $ export LD_LIBRARY_PATH=$mesa/lib
149 $ export EGL_DRIVERS_PATH=$mesa/lib/egl
152 <p>to test a build without installation</p>
156 <li><code>EGL_DRIVER</code>
158 <p>This variable specifies a full path to or the name of an EGL driver. It
159 forces the specified EGL driver to be loaded. It comes in handy when one wants
160 to test a specific driver. This variable is ignored for setuid/setgid
165 <li><code>EGL_PLATFORM</code>
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 <li><code>EGL_LOG_LEVEL</code>
181 <p>This changes the log level of the main library and the drivers. The valid
182 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
183 <code>fatal</code>.</p>
187 <li><code>EGL_SOFTWARE</code>
189 <p>For drivers that support both hardware and software rendering, setting this
190 variable to true forces the use of software rendering.</p>
198 <li><code>egl_dri2</code>
200 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
201 It functions as a DRI driver loader. For <code>x11</code> support, it talks to
202 the X server directly using (XCB-)DRI2 protocol.</p>
204 <p>This driver can share DRI drivers with <code>libGL</code>.</p>
208 <li><code>egl_gallium</code>
210 <p>This driver is based on Gallium3D. It supports all rendering APIs and
211 hardwares supported by Gallium3D. It is the only driver that supports OpenVG.
212 The supported platforms are X11, DRM, FBDEV, and GDI.</p>
214 <p>This driver comes with its own hardware drivers
215 (<code>pipe_<hw></code>) and client API modules
216 (<code>st_<api></code>).</p>
220 <li><code>egl_glx</code>
222 <p>This driver provides a wrapper to GLX. It uses exclusively GLX to implement
223 the EGL API. It supports both direct and indirect rendering when the GLX does.
224 It is accelerated when the GLX is. As such, it cannot provide functions that
225 is not available in GLX or GLX extensions.</p>
231 <p>The ABI between the main library and its drivers are not stable. Nor is
232 there a plan to stabilize it at the moment. Of the EGL drivers,
233 <code>egl_gallium</code> has its own hardware drivers and client API modules.
234 They are considered internal to <code>egl_gallium</code> and there is also no
235 stable ABI between them. These should be kept in mind when packaging for
238 <p>Generally, <code>egl_dri2</code> is preferred over <code>egl_gallium</code>
239 when the system already has DRI drivers. As <code>egl_gallium</code> is loaded
240 before <code>egl_dri2</code> when both are available, <code>egl_gallium</code>
241 is disabled by default.</p>
245 <p>The sources of the main library and the classic drivers can be found at
246 <code>src/egl/</code>. The sources of the <code>egl</code> state tracker can
247 be found at <code>src/gallium/state_trackers/egl/</code>.</p>
249 <p>The suggested way to learn to write a EGL driver is to see how other drivers
250 are written. <code>egl_glx</code> should be a good reference. It works in any
251 environment that has GLX support, and it is simpler than most drivers.</p>
253 <h3>Lifetime of Display Resources</h3>
255 <p>Contexts and surfaces are examples of display resources. They might live
256 longer than the display that creates them.</p>
258 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
259 display resources should be destroyed. Similarly, when a thread is released
260 throught <code>eglReleaseThread</code>, all current display resources should be
261 released. Another way to destory or release resources is through functions
262 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
264 <p>When a resource that is current to some thread is destroyed, the resource
265 should not be destroyed immediately. EGL requires the resource to live until
266 it is no longer current. A driver usually calls
267 <code>eglIs<Resource>Bound</code> to check if a resource is bound
268 (current) to any thread in the destroy callbacks. If it is still bound, the
269 resource is not destroyed.</p>
271 <p>The main library will mark destroyed current resources as unlinked. In a
272 driver's <code>MakeCurrent</code> callback,
273 <code>eglIs<Resource>Linked</code> can then be called to check if a newly
274 released resource is linked to a display. If it is not, the last reference to
275 the resource is removed and the driver should destroy the resource. But it
276 should be careful here because <code>MakeCurrent</code> might be called with an
277 uninitialized display.</p>
279 <p>This is the only mechanism provided by the main library to help manage the
280 resources. The drivers are responsible to the correct behavior as defined by
283 <h3><code>EGL_RENDER_BUFFER</code></h3>
285 <p>In EGL, the color buffer a context should try to render to is decided by the
286 binding surface. It should try to render to the front buffer if the binding
287 surface has <code>EGL_RENDER_BUFFER</code> set to
288 <code>EGL_SINGLE_BUFFER</code>; If the same context is later bound to a
289 surface with <code>EGL_RENDER_BUFFER</code> set to
290 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
291 buffer. However, the context is allowed to make the final decision as to which
292 color buffer it wants to or is able to render to.</p>
294 <p>For pbuffer surfaces, the render buffer is always
295 <code>EGL_BACK_BUFFER</code>. And for pixmap surfaces, the render buffer is
296 always <code>EGL_SINGLE_BUFFER</code>. Unlike window surfaces, EGL spec
297 requires their <code>EGL_RENDER_BUFFER</code> values to be honored. As a
298 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
299 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
300 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
301 pbuffer surfaces.</p>
303 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
304 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them. It
305 is desirable that a driver allocates a private color buffer for each pbuffer
306 surface created. If the window system the driver supports has native pbuffers,
307 or if the native pixmaps have more than one color buffers, the driver should
308 carefully attach the native color buffers to the EGL surfaces, re-route them if
311 <p>There is no defined behavior as to, for example, how
312 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>. Right
313 now, it is desired that the draw buffer in a client API be fixed for pixmap and
314 pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
315 client API renders to the specified render buffer for pixmap and pbuffer
318 <h3><code>EGLDisplay</code> Mutex</h3>
320 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
321 functions (well, except for GetProcAddress which does not take an
322 <code>EGLDisplay</code>). This guarantees that the same dispatch function will
323 not be called with the sample display at the same time. If a driver has access
324 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
325 should as well lock the display before using it.