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  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>fbdev</code>, and <code>gdi</code>.  The <code>gdi</code> platform can
  92 only be built with SCons.  Unless for special needs, the build system should
  93 select the right platforms automatically.</p>
  94
  95 </dd>
  96
  97 <dt><code>--enable-gles1</code></dt>
  98 <dt><code>--enable-gles2</code></dt>
  99 <dd>
 100
 101 <p>These options enable OpenGL ES support in OpenGL.  The result is one big
 102 internal library that supports multiple APIs.</p>
 103
 104 </dd>
 105
 106 <dt><code>--enable-shared-glapi</code></dt>
 107 <dd>
 108
 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>
 112
 113 </dd>
 114
 115 <dt><code>--enable-openvg</code></dt>
 116 <dd>
 117
 118 <p>OpenVG must be explicitly enabled by this option.</p>
 119
 120 </dd>
 121
 122 </dl>
 123
 124 <h2>Use EGL</h2>
 125
 126 <h3>Demos</h3>
 127
 128 <p>There are demos for the client APIs supported by EGL.  They can be found in
 129 mesa/demos repository.</p>
 130
 131 <h3>Environment Variables</h3>
 132
 133 <p>There are several environment variables that control the behavior of EGL at
 134 runtime</p>
 135
 136 <dl>
 137 <dt><code>EGL_DRIVERS_PATH</code></dt>
 138 <dd>
 139
 140 <p>By default, the main library will look for drivers in the directory where
 141 the drivers are installed to.  This variable specifies a list of
 142 colon-separated directories where the main library will look for drivers, in
 143 addition to the default directory.  This variable is ignored for setuid/setgid
 144 binaries.</p>
 145
 146 <p>This variable is usually set to test an uninstalled build.  For example, one
 147 may set</p>
 148
 149 <pre>
 150   $ export LD_LIBRARY_PATH=$mesa/lib
 151   $ export EGL_DRIVERS_PATH=$mesa/lib/egl
 152 </pre>
 153
 154 <p>to test a build without installation</p>
 155
 156 </dd>
 157
 158 <dt><code>EGL_DRIVER</code></dt>
 159 <dd>
 160
 161 <p>This variable specifies a full path to or the name of an EGL driver.  It
 162 forces the specified EGL driver to be loaded.  It comes in handy when one wants
 163 to test a specific driver.  This variable is ignored for setuid/setgid
 164 binaries.</p>
 165
 166 </dd>
 167
 168 <dt><code>EGL_PLATFORM</code></dt>
 169 <dd>
 170
 171 <p>This variable specifies the native platform.  The valid values are the same
 172 as those for <code>--with-egl-platforms</code>.  When the variable is not set,
 173 the main library uses the first platform listed in
 174 <code>--with-egl-platforms</code> as the native platform.</p>
 175
 176 <p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
 177 create displays for non-native platforms.  These extensions are usually used by
 178 applications that support non-native platforms.  Setting this variable is
 179 probably required only for some of the demos found in mesa/demo repository.</p>
 180
 181 </dd>
 182
 183 <dt><code>EGL_LOG_LEVEL</code></dt>
 184 <dd>
 185
 186 <p>This changes the log level of the main library and the drivers.  The valid
 187 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 188 <code>fatal</code>.</p>
 189
 190 </dd>
 191
 192 <dt><code>EGL_SOFTWARE</code></dt>
 193 <dd>
 194
 195 <p>For drivers that support both hardware and software rendering, setting this
 196 variable to true forces the use of software rendering.</p>
 197
 198 </dd>
 199 </dl>
 200
 201 <h2>EGL Drivers</h2>
 202
 203 <dl>
 204 <dt><code>egl_dri2</code></dt>
 205 <dd>
 206
 207 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
 208 It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
 209 the X server directly using (XCB-)DRI2 protocol.</p>
 210
 211 <p>This driver can share DRI drivers with <code>libGL</code>.</p>
 212
 213 </dd>
 214
 215 <h2>Packaging</h2>
 216
 217 <p>The ABI between the main library and its drivers are not stable.  Nor is
 218 there a plan to stabilize it at the moment.</p>
 219
 220 <h2>Developers</h2>
 221
 222 <p>The sources of the main library and drivers can be found at
 223 <code>src/egl/</code>.</p>
 224
 225 <h3>Lifetime of Display Resources</h3>
 226
 227 <p>Contexts and surfaces are examples of display resources.  They might live
 228 longer than the display that creates them.</p>
 229
 230 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 231 display resources should be destroyed.  Similarly, when a thread is released
 232 through <code>eglReleaseThread</code>, all current display resources should be
 233 released.  Another way to destroy or release resources is through functions
 234 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 235
 236 <p>When a resource that is current to some thread is destroyed, the resource
 237 should not be destroyed immediately.  EGL requires the resource to live until
 238 it is no longer current.  A driver usually calls
 239 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 240 (current) to any thread in the destroy callbacks.  If it is still bound, the
 241 resource is not destroyed.</p>
 242
 243 <p>The main library will mark destroyed current resources as unlinked.  In a
 244 driver's <code>MakeCurrent</code> callback,
 245 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 246 released resource is linked to a display.  If it is not, the last reference to
 247 the resource is removed and the driver should destroy the resource.  But it
 248 should be careful here because <code>MakeCurrent</code> might be called with an
 249 uninitialized display.</p>
 250
 251 <p>This is the only mechanism provided by the main library to help manage the
 252 resources.  The drivers are responsible to the correct behavior as defined by
 253 EGL.</p>
 254
 255 <h3><code>EGL_RENDER_BUFFER</code></h3>
 256
 257 <p>In EGL, the color buffer a context should try to render to is decided by the
 258 binding surface.  It should try to render to the front buffer if the binding
 259 surface has <code>EGL_RENDER_BUFFER</code> set to
 260 <code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
 261 surface with <code>EGL_RENDER_BUFFER</code> set to
 262 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
 263 buffer.  However, the context is allowed to make the final decision as to which
 264 color buffer it wants to or is able to render to.</p>
 265
 266 <p>For pbuffer surfaces, the render buffer is always
 267 <code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
 268 always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
 269 requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
 270 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
 271 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
 272 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
 273 pbuffer surfaces.</p>
 274
 275 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
 276 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
 277 is desirable that a driver allocates a private color buffer for each pbuffer
 278 surface created.  If the window system the driver supports has native pbuffers,
 279 or if the native pixmaps have more than one color buffers, the driver should
 280 carefully attach the native color buffers to the EGL surfaces, re-route them if
 281 required.</p>
 282
 283 <p>There is no defined behavior as to, for example, how
 284 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
 285 now, it is desired that the draw buffer in a client API be fixed for pixmap and
 286 pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
 287 client API renders to the specified render buffer for pixmap and pbuffer
 288 surfaces.</p>
 289
 290 <h3><code>EGLDisplay</code> Mutex</h3>
 291
 292 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 293 functions (well, except for GetProcAddress which does not take an
 294 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 295 not be called with the sample display at the same time.  If a driver has access
 296 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 297 should as well lock the display before using it.
 298
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