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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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5  <title>Mesa EGL</title>
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8<body>
9
10<div class="header">
11  <h1>The Mesa 3D Graphics Library</h1>
12</div>
13
14<iframe src="contents.html"></iframe>
15<div class="content">
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="https://www.khronos.org/egl/">
22https://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 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-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-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.</p>
87
88<p>The available platforms are <code>x11</code>, <code>drm</code>,
89<code>wayland</code>, <code>surfaceless</code>, <code>android</code>,
90and <code>haiku</code>.
91The <code>android</code> platform can either be built as a system
92component, part of AOSP, using <code>Android.mk</code> files, or
93cross-compiled using appropriate <code>configure</code> options.
94The <code>haiku</code> platform can only be built with SCons.
95Unless for special needs, the build system should
96select the right platforms automatically.</p>
97
98</dd>
99
100<dt><code>--enable-gles1</code></dt>
101<dt><code>--enable-gles2</code></dt>
102<dd>
103
104<p>These options enable OpenGL ES support in OpenGL.  The result is one big
105internal library that supports multiple APIs.</p>
106
107</dd>
108
109<dt><code>--enable-shared-glapi</code></dt>
110<dd>
111
112<p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
113This options makes <code>libGL</code> use the shared <code>libglapi</code>.  This
114is required if applications mix OpenGL and OpenGL ES.</p>
115
116</dd>
117
118</dl>
119
120<h2>Use EGL</h2>
121
122<h3>Demos</h3>
123
124<p>There are demos for the client APIs supported by EGL.  They can be found in
125mesa/demos repository.</p>
126
127<h3>Environment Variables</h3>
128
129<p>There are several environment variables that control the behavior of EGL at
130runtime</p>
131
132<dl>
133<dt><code>EGL_PLATFORM</code></dt>
134<dd>
135
136<p>This variable specifies the native platform.  The valid values are the same
137as those for <code>--with-platforms</code>.  When the variable is not set,
138the main library uses the first platform listed in
139<code>--with-platforms</code> as the native platform.</p>
140
141<p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
142create displays for non-native platforms.  These extensions are usually used by
143applications that support non-native platforms.  Setting this variable is
144probably required only for some of the demos found in mesa/demo repository.</p>
145
146</dd>
147
148<dt><code>EGL_LOG_LEVEL</code></dt>
149<dd>
150
151<p>This changes the log level of the main library and the drivers.  The valid
152values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
153<code>fatal</code>.</p>
154
155</dd>
156</dl>
157
158<h2>EGL Drivers</h2>
159
160<dl>
161<dt><code>egl_dri2</code></dt>
162<dd>
163
164<p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
165It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
166the X server directly using (XCB-)DRI2 protocol.</p>
167
168<p>This driver can share DRI drivers with <code>libGL</code>.</p>
169
170</dd>
171
172<h2>Packaging</h2>
173
174<p>The ABI between the main library and its drivers are not stable.  Nor is
175there a plan to stabilize it at the moment.</p>
176
177<h2>Developers</h2>
178
179<p>The sources of the main library and drivers can be found at
180<code>src/egl/</code>.</p>
181
182<h3>Lifetime of Display Resources</h3>
183
184<p>Contexts and surfaces are examples of display resources.  They might live
185longer than the display that creates them.</p>
186
187<p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
188display resources should be destroyed.  Similarly, when a thread is released
189through <code>eglReleaseThread</code>, all current display resources should be
190released.  Another way to destroy or release resources is through functions
191such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
192
193<p>When a resource that is current to some thread is destroyed, the resource
194should not be destroyed immediately.  EGL requires the resource to live until
195it is no longer current.  A driver usually calls
196<code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
197(current) to any thread in the destroy callbacks.  If it is still bound, the
198resource is not destroyed.</p>
199
200<p>The main library will mark destroyed current resources as unlinked.  In a
201driver's <code>MakeCurrent</code> callback,
202<code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
203released resource is linked to a display.  If it is not, the last reference to
204the resource is removed and the driver should destroy the resource.  But it
205should be careful here because <code>MakeCurrent</code> might be called with an
206uninitialized display.</p>
207
208<p>This is the only mechanism provided by the main library to help manage the
209resources.  The drivers are responsible to the correct behavior as defined by
210EGL.</p>
211
212<h3><code>EGL_RENDER_BUFFER</code></h3>
213
214<p>In EGL, the color buffer a context should try to render to is decided by the
215binding surface.  It should try to render to the front buffer if the binding
216surface has <code>EGL_RENDER_BUFFER</code> set to
217<code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
218surface with <code>EGL_RENDER_BUFFER</code> set to
219<code>EGL_BACK_BUFFER</code>, the context should try to render to the back
220buffer.  However, the context is allowed to make the final decision as to which
221color buffer it wants to or is able to render to.</p>
222
223<p>For pbuffer surfaces, the render buffer is always
224<code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
225always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
226requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
227result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
228<code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
229config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
230pbuffer surfaces.</p>
231
232<p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
233single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
234is desirable that a driver allocates a private color buffer for each pbuffer
235surface created.  If the window system the driver supports has native pbuffers,
236or if the native pixmaps have more than one color buffers, the driver should
237carefully attach the native color buffers to the EGL surfaces, re-route them if
238required.</p>
239
240<p>There is no defined behavior as to, for example, how
241<code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
242now, it is desired that the draw buffer in a client API be fixed for pixmap and
243pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
244client API renders to the specified render buffer for pixmap and pbuffer
245surfaces.</p>
246
247<h3><code>EGLDisplay</code> Mutex</h3>
248
249The <code>EGLDisplay</code> will be locked before calling any of the dispatch
250functions (well, except for GetProcAddress which does not take an
251<code>EGLDisplay</code>).  This guarantees that the same dispatch function will
252not be called with the sample display at the same time.  If a driver has access
253to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
254should as well lock the display before using it.
255
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