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