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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
  20 about EGL can be found at
  21 <a href="http://www.khronos.org/egl/">
  22 http://www.khronos.org/egl/</a>.</p>
  23
  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>
  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
  37 the 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
  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>
  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
  56 or 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
  61 time</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
  68 will 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
  76 drivers 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
  84 separated string such as <code>--with-egl-platforms=x11,drm</code>.  It decides
  85 the platforms a driver may support.  The first listed platform is also used by
  86 the main library to decide the native platform: the platform the EGL native
  87 types 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>,
  92 and <code>haiku</code>.  The <code>android</code> platform
  93 can only be built as a system component, part of AOSP, while the
  94 <code>haiku</code> platform can only be built with SCons.
  95 Unless for special needs, the build system should
  96 select 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
 105 internal 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>.
 113 This options makes <code>libGL</code> use the shared <code>libglapi</code>.  This
 114 is 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
 125 mesa/demos repository.</p>
 126
 127 <h3>Environment Variables</h3>
 128
 129 <p>There are several environment variables that control the behavior of EGL at
 130 runtime</p>
 131
 132 <dl>
 133 <dt><code>EGL_DRIVERS_PATH</code></dt>
 134 <dd>
 135
 136 <p>By default, the main library will look for drivers in the directory where
 137 the drivers are installed to.  This variable specifies a list of
 138 colon-separated directories where the main library will look for drivers, in
 139 addition to the default directory.  This variable is ignored for setuid/setgid
 140 binaries.</p>
 141
 142 <p>This variable is usually set to test an uninstalled build.  For example, one
 143 may set</p>
 144
 145 <pre>
 146   $ export LD_LIBRARY_PATH=$mesa/lib
 147   $ export EGL_DRIVERS_PATH=$mesa/lib/egl
 148 </pre>
 149
 150 <p>to test a build without installation</p>
 151
 152 </dd>
 153
 154 <dt><code>EGL_DRIVER</code></dt>
 155 <dd>
 156
 157 <p>This variable specifies a full path to or the name of an EGL driver.  It
 158 forces the specified EGL driver to be loaded.  It comes in handy when one wants
 159 to test a specific driver.  This variable is ignored for setuid/setgid
 160 binaries.</p>
 161
 162 </dd>
 163
 164 <dt><code>EGL_PLATFORM</code></dt>
 165 <dd>
 166
 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>
 171
 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>
 176
 177 </dd>
 178
 179 <dt><code>EGL_LOG_LEVEL</code></dt>
 180 <dd>
 181
 182 <p>This changes the log level of the main library and the drivers.  The valid
 183 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 184 <code>fatal</code>.</p>
 185
 186 </dd>
 187 </dl>
 188
 189 <h2>EGL Drivers</h2>
 190
 191 <dl>
 192 <dt><code>egl_dri2</code></dt>
 193 <dd>
 194
 195 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
 196 It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
 197 the X server directly using (XCB-)DRI2 protocol.</p>
 198
 199 <p>This driver can share DRI drivers with <code>libGL</code>.</p>
 200
 201 </dd>
 202
 203 <h2>Packaging</h2>
 204
 205 <p>The ABI between the main library and its drivers are not stable.  Nor is
 206 there a plan to stabilize it at the moment.</p>
 207
 208 <h2>Developers</h2>
 209
 210 <p>The sources of the main library and drivers can be found at
 211 <code>src/egl/</code>.</p>
 212
 213 <h3>Lifetime of Display Resources</h3>
 214
 215 <p>Contexts and surfaces are examples of display resources.  They might live
 216 longer than the display that creates them.</p>
 217
 218 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 219 display resources should be destroyed.  Similarly, when a thread is released
 220 through <code>eglReleaseThread</code>, all current display resources should be
 221 released.  Another way to destroy or release resources is through functions
 222 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 223
 224 <p>When a resource that is current to some thread is destroyed, the resource
 225 should not be destroyed immediately.  EGL requires the resource to live until
 226 it is no longer current.  A driver usually calls
 227 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 228 (current) to any thread in the destroy callbacks.  If it is still bound, the
 229 resource is not destroyed.</p>
 230
 231 <p>The main library will mark destroyed current resources as unlinked.  In a
 232 driver's <code>MakeCurrent</code> callback,
 233 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 234 released resource is linked to a display.  If it is not, the last reference to
 235 the resource is removed and the driver should destroy the resource.  But it
 236 should be careful here because <code>MakeCurrent</code> might be called with an
 237 uninitialized display.</p>
 238
 239 <p>This is the only mechanism provided by the main library to help manage the
 240 resources.  The drivers are responsible to the correct behavior as defined by
 241 EGL.</p>
 242
 243 <h3><code>EGL_RENDER_BUFFER</code></h3>
 244
 245 <p>In EGL, the color buffer a context should try to render to is decided by the
 246 binding surface.  It should try to render to the front buffer if the binding
 247 surface has <code>EGL_RENDER_BUFFER</code> set to
 248 <code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
 249 surface with <code>EGL_RENDER_BUFFER</code> set to
 250 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
 251 buffer.  However, the context is allowed to make the final decision as to which
 252 color buffer it wants to or is able to render to.</p>
 253
 254 <p>For pbuffer surfaces, the render buffer is always
 255 <code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
 256 always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
 257 requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
 258 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
 259 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
 260 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
 261 pbuffer surfaces.</p>
 262
 263 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
 264 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
 265 is desirable that a driver allocates a private color buffer for each pbuffer
 266 surface created.  If the window system the driver supports has native pbuffers,
 267 or if the native pixmaps have more than one color buffers, the driver should
 268 carefully attach the native color buffers to the EGL surfaces, re-route them if
 269 required.</p>
 270
 271 <p>There is no defined behavior as to, for example, how
 272 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
 273 now, it is desired that the draw buffer in a client API be fixed for pixmap and
 274 pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
 275 client API renders to the specified render buffer for pixmap and pbuffer
 276 surfaces.</p>
 277
 278 <h3><code>EGLDisplay</code> Mutex</h3>
 279
 280 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 281 functions (well, except for GetProcAddress which does not take an
 282 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 283 not be called with the sample display at the same time.  If a driver has access
 284 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 285 should as well lock the display before using it.
 286
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