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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>--enable-gallium-egl</code></dt>
  81 <dd>
  82
  83 <p>Enable the optional <code>egl_gallium</code> driver.</p>
  84
  85 </dd>
  86
  87 <dt><code>--with-egl-platforms</code></dt>
  88 <dd>
  89
  90 <p>List the platforms (window systems) to support.  Its argument is a comma
  91 seprated string such as <code>--with-egl-platforms=x11,drm</code>.  It decides
  92 the platforms a driver may support.  The first listed platform is also used by
  93 the main library to decide the native platform: the platform the EGL native
  94 types such as <code>EGLNativeDisplayType</code> or
  95 <code>EGLNativeWindowType</code> defined for.</p>
  96
  97 <p>The available platforms are <code>x11</code>, <code>drm</code>,
  98 <code>fbdev</code>, and <code>gdi</code>.  The <code>gdi</code> platform can
  99 only be built with SCons.  Unless for special needs, the build system should
 100 select the right platforms automatically.</p>
 101
 102 </dd>
 103
 104 <dt><code>--enable-gles1</code></dt>
 105 <dt><code>--enable-gles2</code></dt>
 106 <dd>
 107
 108 <p>These options enable OpenGL ES support in OpenGL.  The result is one big
 109 internal library that supports multiple APIs.</p>
 110
 111 </dd>
 112
 113 <dt><code>--enable-shared-glapi</code></dt>
 114 <dd>
 115
 116 <p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
 117 This options makes <code>libGL</code> use the shared <code>libglapi</code>.  This
 118 is required if applications mix OpenGL and OpenGL ES.</p>
 119
 120 </dd>
 121
 122 <dt><code>--enable-openvg</code></dt>
 123 <dd>
 124
 125 <p>OpenVG must be explicitly enabled by this option.</p>
 126
 127 </dd>
 128
 129 </dl>
 130
 131 <h2>Use EGL</h2>
 132
 133 <h3>Demos</h3>
 134
 135 <p>There are demos for the client APIs supported by EGL.  They can be found in
 136 mesa/demos repository.</p>
 137
 138 <h3>Environment Variables</h3>
 139
 140 <p>There are several environment variables that control the behavior of EGL at
 141 runtime</p>
 142
 143 <dl>
 144 <dt><code>EGL_DRIVERS_PATH</code></dt>
 145 <dd>
 146
 147 <p>By default, the main library will look for drivers in the directory where
 148 the drivers are installed to.  This variable specifies a list of
 149 colon-separated directories where the main library will look for drivers, in
 150 addition to the default directory.  This variable is ignored for setuid/setgid
 151 binaries.</p>
 152
 153 <p>This variable is usually set to test an uninstalled build.  For example, one
 154 may set</p>
 155
 156 <pre>
 157   $ export LD_LIBRARY_PATH=$mesa/lib
 158   $ export EGL_DRIVERS_PATH=$mesa/lib/egl
 159 </pre>
 160
 161 <p>to test a build without installation</p>
 162
 163 </dd>
 164
 165 <dt><code>EGL_DRIVER</code></dt>
 166 <dd>
 167
 168 <p>This variable specifies a full path to or the name of an EGL driver.  It
 169 forces the specified EGL driver to be loaded.  It comes in handy when one wants
 170 to test a specific driver.  This variable is ignored for setuid/setgid
 171 binaries.</p>
 172
 173 </dd>
 174
 175 <dt><code>EGL_PLATFORM</code></dt>
 176 <dd>
 177
 178 <p>This variable specifies the native platform.  The valid values are the same
 179 as those for <code>--with-egl-platforms</code>.  When the variable is not set,
 180 the main library uses the first platform listed in
 181 <code>--with-egl-platforms</code> as the native platform.</p>
 182
 183 <p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
 184 create displays for non-native platforms.  These extensions are usually used by
 185 applications that support non-native platforms.  Setting this variable is
 186 probably required only for some of the demos found in mesa/demo repository.</p>
 187
 188 </dd>
 189
 190 <dt><code>EGL_LOG_LEVEL</code></dt>
 191 <dd>
 192
 193 <p>This changes the log level of the main library and the drivers.  The valid
 194 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 195 <code>fatal</code>.</p>
 196
 197 </dd>
 198
 199 <dt><code>EGL_SOFTWARE</code></dt>
 200 <dd>
 201
 202 <p>For drivers that support both hardware and software rendering, setting this
 203 variable to true forces the use of software rendering.</p>
 204
 205 </dd>
 206 </dl>
 207
 208 <h2>EGL Drivers</h2>
 209
 210 <dl>
 211 <dt><code>egl_dri2</code></dt>
 212 <dd>
 213
 214 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
 215 It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
 216 the X server directly using (XCB-)DRI2 protocol.</p>
 217
 218 <p>This driver can share DRI drivers with <code>libGL</code>.</p>
 219
 220 </dd>
 221
 222 <dt><code>egl_gallium</code></dt>
 223 <dd>
 224
 225 <p>This driver is based on Gallium3D.  It supports all rendering APIs and
 226 hardwares supported by Gallium3D.  It is the only driver that supports OpenVG.
 227 The supported platforms are X11, DRM, FBDEV, and GDI.</p>
 228
 229 <p>This driver comes with its own hardware drivers
 230 (<code>pipe_&lt;hw&gt;</code>) and client API modules
 231 (<code>st_&lt;api&gt;</code>).</p>
 232
 233 </dd>
 234
 235 <dt><code>egl_glx</code></dt>
 236 <dd>
 237
 238 <p>This driver provides a wrapper to GLX.  It uses exclusively GLX to implement
 239 the EGL API.  It supports both direct and indirect rendering when the GLX does.
 240 It is accelerated when the GLX is.  As such, it cannot provide functions that
 241 is not available in GLX or GLX extensions.</p>
 242 </dd>
 243 </dl>
 244
 245 <h2>Packaging</h2>
 246
 247 <p>The ABI between the main library and its drivers are not stable.  Nor is
 248 there a plan to stabilize it at the moment.  Of the EGL drivers,
 249 <code>egl_gallium</code> has its own hardware drivers and client API modules.
 250 They are considered internal to <code>egl_gallium</code> and there is also no
 251 stable ABI between them.  These should be kept in mind when packaging for
 252 distribution.</p>
 253
 254 <p>Generally, <code>egl_dri2</code> is preferred over <code>egl_gallium</code>
 255 when the system already has DRI drivers.  As <code>egl_gallium</code> is loaded
 256 before <code>egl_dri2</code> when both are available, <code>egl_gallium</code>
 257 is disabled by default.</p>
 258
 259 <h2>Developers</h2>
 260
 261 <p>The sources of the main library and the classic drivers can be found at
 262 <code>src/egl/</code>.  The sources of the <code>egl</code> state tracker can
 263 be found at <code>src/gallium/state_trackers/egl/</code>.</p>
 264
 265 <p>The suggested way to learn to write a EGL driver is to see how other drivers
 266 are written.  <code>egl_glx</code> should be a good reference.  It works in any
 267 environment that has GLX support, and it is simpler than most drivers.</p>
 268
 269 <h3>Lifetime of Display Resources</h3>
 270
 271 <p>Contexts and surfaces are examples of display resources.  They might live
 272 longer than the display that creates them.</p>
 273
 274 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 275 display resources should be destroyed.  Similarly, when a thread is released
 276 throught <code>eglReleaseThread</code>, all current display resources should be
 277 released.  Another way to destory or release resources is through functions
 278 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 279
 280 <p>When a resource that is current to some thread is destroyed, the resource
 281 should not be destroyed immediately.  EGL requires the resource to live until
 282 it is no longer current.  A driver usually calls
 283 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 284 (current) to any thread in the destroy callbacks.  If it is still bound, the
 285 resource is not destroyed.</p>
 286
 287 <p>The main library will mark destroyed current resources as unlinked.  In a
 288 driver's <code>MakeCurrent</code> callback,
 289 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 290 released resource is linked to a display.  If it is not, the last reference to
 291 the resource is removed and the driver should destroy the resource.  But it
 292 should be careful here because <code>MakeCurrent</code> might be called with an
 293 uninitialized display.</p>
 294
 295 <p>This is the only mechanism provided by the main library to help manage the
 296 resources.  The drivers are responsible to the correct behavior as defined by
 297 EGL.</p>
 298
 299 <h3><code>EGL_RENDER_BUFFER</code></h3>
 300
 301 <p>In EGL, the color buffer a context should try to render to is decided by the
 302 binding surface.  It should try to render to the front buffer if the binding
 303 surface has <code>EGL_RENDER_BUFFER</code> set to
 304 <code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
 305 surface with <code>EGL_RENDER_BUFFER</code> set to
 306 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
 307 buffer.  However, the context is allowed to make the final decision as to which
 308 color buffer it wants to or is able to render to.</p>
 309
 310 <p>For pbuffer surfaces, the render buffer is always
 311 <code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
 312 always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
 313 requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
 314 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
 315 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
 316 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
 317 pbuffer surfaces.</p>
 318
 319 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
 320 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
 321 is desirable that a driver allocates a private color buffer for each pbuffer
 322 surface created.  If the window system the driver supports has native pbuffers,
 323 or if the native pixmaps have more than one color buffers, the driver should
 324 carefully attach the native color buffers to the EGL surfaces, re-route them if
 325 required.</p>
 326
 327 <p>There is no defined behavior as to, for example, how
 328 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
 329 now, it is desired that the draw buffer in a client API be fixed for pixmap and
 330 pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
 331 client API renders to the specified render buffer for pixmap and pbuffer
 332 surfaces.</p>
 333
 334 <h3><code>EGLDisplay</code> Mutex</h3>
 335
 336 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 337 functions (well, except for GetProcAddress which does not take an
 338 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 339 not be called with the sample display at the same time.  If a driver has access
 340 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 341 should as well lock the display before using it.
 342
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