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10<div class="header">
11  <h1>The Mesa 3D Graphics Library</h1>
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16
17<h1>Mesa EGL</h1>
18
19<p>The current version of EGL in Mesa implements EGL 1.4.  More information
20about EGL can be found at
21<a href="http://www.khronos.org/egl/">
22http://www.khronos.org/egl/</a>.</p>
23
24<p>The Mesa's implementation of EGL uses a driver architecture.  The main
25library (<code>libEGL</code>) is window system neutral.  It provides the EGL
26API entry points and helper functions for use by the drivers.  Drivers are
27dynamically loaded by the main library and most of the EGL API calls are
28directly dispatched to the drivers.</p>
29
30<p>The driver in use decides the window system to support.</p>
31
32<h2>Build EGL</h2>
33
34<ol>
35<li>
36<p>Run <code>configure</code> with the desired client APIs and enable
37the driver for your hardware.  For example</p>
38
39<pre>
40  $ ./configure --enable-gles1 --enable-gles2 \
41                --with-dri-drivers=... \
42                --with-gallium-drivers=...
43</pre>
44
45<p>The main library and OpenGL is enabled by default.  The first two options
46above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>.  The last two
47options enables the listed classic and and Gallium drivers respectively.</p>
48
49</li>
50
51<li>Build and install Mesa as usual.</li>
52</ol>
53
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
56or more EGL drivers.</p>
57
58<h3>Configure Options</h3>
59
60<p>There are several options that control the build of EGL at configuration
61time</p>
62
63<dl>
64<dt><code>--enable-egl</code></dt>
65<dd>
66
67<p>By default, EGL is enabled.  When disabled, the main library and the drivers
68will not be built.</p>
69
70</dd>
71
72<dt><code>--with-egl-driver-dir</code></dt>
73<dd>
74
75<p>The directory EGL drivers should be installed to.  If not specified, EGL
76drivers will be installed to <code>${libdir}/egl</code>.</p>
77
78</dd>
79
80<dt><code>--with-egl-platforms</code></dt>
81<dd>
82
83<p>List the platforms (window systems) to support.  Its argument is a comma
84separated string such as <code>--with-egl-platforms=x11,drm</code>.  It decides
85the platforms a driver may support.  The first listed platform is also used by
86the main library to decide the native platform: the platform the EGL native
87types such as <code>EGLNativeDisplayType</code> or
88<code>EGLNativeWindowType</code> defined for.</p>
89
90<p>The available platforms are <code>x11</code>, <code>drm</code>,
91<code>wayland</code>, <code>surfaceless</code>, <code>android</code>,
92and <code>haiku</code>.
93The <code>android</code> platform can either be built as a system
94component, part of AOSP, using <code>Android.mk</code> files, or
95cross-compiled using appropriate <code>configure</code> options.
96The <code>haiku</code> platform can only be built with SCons.
97Unless for special needs, the build system should
98select the right platforms automatically.</p>
99
100</dd>
101
102<dt><code>--enable-gles1</code></dt>
103<dt><code>--enable-gles2</code></dt>
104<dd>
105
106<p>These options enable OpenGL ES support in OpenGL.  The result is one big
107internal library that supports multiple APIs.</p>
108
109</dd>
110
111<dt><code>--enable-shared-glapi</code></dt>
112<dd>
113
114<p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
115This options makes <code>libGL</code> use the shared <code>libglapi</code>.  This
116is required if applications mix OpenGL and OpenGL ES.</p>
117
118</dd>
119
120</dl>
121
122<h2>Use EGL</h2>
123
124<h3>Demos</h3>
125
126<p>There are demos for the client APIs supported by EGL.  They can be found in
127mesa/demos repository.</p>
128
129<h3>Environment Variables</h3>
130
131<p>There are several environment variables that control the behavior of EGL at
132runtime</p>
133
134<dl>
135<dt><code>EGL_DRIVERS_PATH</code></dt>
136<dd>
137
138<p>By default, the main library will look for drivers in the directory where
139the drivers are installed to.  This variable specifies a list of
140colon-separated directories where the main library will look for drivers, in
141addition to the default directory.  This variable is ignored for setuid/setgid
142binaries.</p>
143
144<p>This variable is usually set to test an uninstalled build.  For example, one
145may set</p>
146
147<pre>
148  $ export LD_LIBRARY_PATH=$mesa/lib
149  $ export EGL_DRIVERS_PATH=$mesa/lib/egl
150</pre>
151
152<p>to test a build without installation</p>
153
154</dd>
155
156<dt><code>EGL_DRIVER</code></dt>
157<dd>
158
159<p>This variable specifies a full path to or the name of an EGL driver.  It
160forces the specified EGL driver to be loaded.  It comes in handy when one wants
161to test a specific driver.  This variable is ignored for setuid/setgid
162binaries.</p>
163
164</dd>
165
166<dt><code>EGL_PLATFORM</code></dt>
167<dd>
168
169<p>This variable specifies the native platform.  The valid values are the same
170as those for <code>--with-egl-platforms</code>.  When the variable is not set,
171the main library uses the first platform listed in
172<code>--with-egl-platforms</code> as the native platform.</p>
173
174<p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
175create displays for non-native platforms.  These extensions are usually used by
176applications that support non-native platforms.  Setting this variable is
177probably required only for some of the demos found in mesa/demo repository.</p>
178
179</dd>
180
181<dt><code>EGL_LOG_LEVEL</code></dt>
182<dd>
183
184<p>This changes the log level of the main library and the drivers.  The valid
185values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
186<code>fatal</code>.</p>
187
188</dd>
189</dl>
190
191<h2>EGL Drivers</h2>
192
193<dl>
194<dt><code>egl_dri2</code></dt>
195<dd>
196
197<p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
198It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
199the X server directly using (XCB-)DRI2 protocol.</p>
200
201<p>This driver can share DRI drivers with <code>libGL</code>.</p>
202
203</dd>
204
205<h2>Packaging</h2>
206
207<p>The ABI between the main library and its drivers are not stable.  Nor is
208there a plan to stabilize it at the moment.</p>
209
210<h2>Developers</h2>
211
212<p>The sources of the main library and drivers can be found at
213<code>src/egl/</code>.</p>
214
215<h3>Lifetime of Display Resources</h3>
216
217<p>Contexts and surfaces are examples of display resources.  They might live
218longer than the display that creates them.</p>
219
220<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
221display resources should be destroyed.  Similarly, when a thread is released
222through <code>eglReleaseThread</code>, all current display resources should be
223released.  Another way to destroy or release resources is through functions
224such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
225
226<p>When a resource that is current to some thread is destroyed, the resource
227should not be destroyed immediately.  EGL requires the resource to live until
228it is no longer current.  A driver usually calls
229<code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
230(current) to any thread in the destroy callbacks.  If it is still bound, the
231resource is not destroyed.</p>
232
233<p>The main library will mark destroyed current resources as unlinked.  In a
234driver's <code>MakeCurrent</code> callback,
235<code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
236released resource is linked to a display.  If it is not, the last reference to
237the resource is removed and the driver should destroy the resource.  But it
238should be careful here because <code>MakeCurrent</code> might be called with an
239uninitialized display.</p>
240
241<p>This is the only mechanism provided by the main library to help manage the
242resources.  The drivers are responsible to the correct behavior as defined by
243EGL.</p>
244
245<h3><code>EGL_RENDER_BUFFER</code></h3>
246
247<p>In EGL, the color buffer a context should try to render to is decided by the
248binding surface.  It should try to render to the front buffer if the binding
249surface has <code>EGL_RENDER_BUFFER</code> set to
250<code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
251surface with <code>EGL_RENDER_BUFFER</code> set to
252<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
253buffer.  However, the context is allowed to make the final decision as to which
254color buffer it wants to or is able to render to.</p>
255
256<p>For pbuffer surfaces, the render buffer is always
257<code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
258always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
259requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
260result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
261<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
262config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
263pbuffer surfaces.</p>
264
265<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
266single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
267is desirable that a driver allocates a private color buffer for each pbuffer
268surface created.  If the window system the driver supports has native pbuffers,
269or if the native pixmaps have more than one color buffers, the driver should
270carefully attach the native color buffers to the EGL surfaces, re-route them if
271required.</p>
272
273<p>There is no defined behavior as to, for example, how
274<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
275now, it is desired that the draw buffer in a client API be fixed for pixmap and
276pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
277client API renders to the specified render buffer for pixmap and pbuffer
278surfaces.</p>
279
280<h3><code>EGLDisplay</code> Mutex</h3>
281
282The <code>EGLDisplay</code> will be locked before calling any of the dispatch
283functions (well, except for GetProcAddress which does not take an
284<code>EGLDisplay</code>).  This guarantees that the same dispatch function will
285not be called with the sample display at the same time.  If a driver has access
286to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
287should as well lock the display before using it.
288
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