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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="https://www.khronos.org/egl/">
  22 https://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: this defines EGL native
  87 types such as <code>EGLNativeDisplayType</code> or
  88 <code>EGLNativeWindowType</code>.</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>.
  93 The <code>android</code> platform can either be built as a system
  94 component, part of AOSP, using <code>Android.mk</code> files, or
  95 cross-compiled using appropriate <code>configure</code> options.
  96 The <code>haiku</code> platform can only be built with SCons.
  97 Unless for special needs, the build system should
  98 select the right platforms automatically.</p>
  99
 100 </dd>
 101
 102 <dt><code>--enable-gles1</code></dt>
 103 <dt><code>--enable-gles2</code></dt>
 104 <dd>
 105
 106 <p>These options enable OpenGL ES support in OpenGL.  The result is one big
 107 internal library that supports multiple APIs.</p>
 108
 109 </dd>
 110
 111 <dt><code>--enable-shared-glapi</code></dt>
 112 <dd>
 113
 114 <p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
 115 This options makes <code>libGL</code> use the shared <code>libglapi</code>.  This
 116 is required if applications mix OpenGL and OpenGL ES.</p>
 117
 118 </dd>
 119
 120 </dl>
 121
 122 <h2>Use EGL</h2>
 123
 124 <h3>Demos</h3>
 125
 126 <p>There are demos for the client APIs supported by EGL.  They can be found in
 127 mesa/demos repository.</p>
 128
 129 <h3>Environment Variables</h3>
 130
 131 <p>There are several environment variables that control the behavior of EGL at
 132 runtime</p>
 133
 134 <dl>
 135 <dt><code>EGL_DRIVERS_PATH</code></dt>
 136 <dd>
 137
 138 <p>By default, the main library will look for drivers in the directory where
 139 the drivers are installed to.  This variable specifies a list of
 140 colon-separated directories where the main library will look for drivers, in
 141 addition to the default directory.  This variable is ignored for setuid/setgid
 142 binaries.</p>
 143
 144 <p>This variable is usually set to test an uninstalled build.  For example, one
 145 may set</p>
 146
 147 <pre>
 148   $ export LD_LIBRARY_PATH=$mesa/lib
 149   $ export EGL_DRIVERS_PATH=$mesa/lib/egl
 150 </pre>
 151
 152 <p>to test a build without installation</p>
 153
 154 </dd>
 155
 156 <dt><code>EGL_DRIVER</code></dt>
 157 <dd>
 158
 159 <p>This variable specifies a full path to or the name of an EGL driver.  It
 160 forces the specified EGL driver to be loaded.  It comes in handy when one wants
 161 to test a specific driver.  This variable is ignored for setuid/setgid
 162 binaries.</p>
 163
 164 </dd>
 165
 166 <dt><code>EGL_PLATFORM</code></dt>
 167 <dd>
 168
 169 <p>This variable specifies the native platform.  The valid values are the same
 170 as those for <code>--with-egl-platforms</code>.  When the variable is not set,
 171 the main library uses the first platform listed in
 172 <code>--with-egl-platforms</code> as the native platform.</p>
 173
 174 <p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
 175 create displays for non-native platforms.  These extensions are usually used by
 176 applications that support non-native platforms.  Setting this variable is
 177 probably required only for some of the demos found in mesa/demo repository.</p>
 178
 179 </dd>
 180
 181 <dt><code>EGL_LOG_LEVEL</code></dt>
 182 <dd>
 183
 184 <p>This changes the log level of the main library and the drivers.  The valid
 185 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 186 <code>fatal</code>.</p>
 187
 188 </dd>
 189 </dl>
 190
 191 <h2>EGL Drivers</h2>
 192
 193 <dl>
 194 <dt><code>egl_dri2</code></dt>
 195 <dd>
 196
 197 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
 198 It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
 199 the X server directly using (XCB-)DRI2 protocol.</p>
 200
 201 <p>This driver can share DRI drivers with <code>libGL</code>.</p>
 202
 203 </dd>
 204
 205 <h2>Packaging</h2>
 206
 207 <p>The ABI between the main library and its drivers are not stable.  Nor is
 208 there a plan to stabilize it at the moment.</p>
 209
 210 <h2>Developers</h2>
 211
 212 <p>The sources of the main library and drivers can be found at
 213 <code>src/egl/</code>.</p>
 214
 215 <h3>Lifetime of Display Resources</h3>
 216
 217 <p>Contexts and surfaces are examples of display resources.  They might live
 218 longer than the display that creates them.</p>
 219
 220 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 221 display resources should be destroyed.  Similarly, when a thread is released
 222 through <code>eglReleaseThread</code>, all current display resources should be
 223 released.  Another way to destroy or release resources is through functions
 224 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 225
 226 <p>When a resource that is current to some thread is destroyed, the resource
 227 should not be destroyed immediately.  EGL requires the resource to live until
 228 it is no longer current.  A driver usually calls
 229 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 230 (current) to any thread in the destroy callbacks.  If it is still bound, the
 231 resource is not destroyed.</p>
 232
 233 <p>The main library will mark destroyed current resources as unlinked.  In a
 234 driver's <code>MakeCurrent</code> callback,
 235 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 236 released resource is linked to a display.  If it is not, the last reference to
 237 the resource is removed and the driver should destroy the resource.  But it
 238 should be careful here because <code>MakeCurrent</code> might be called with an
 239 uninitialized display.</p>
 240
 241 <p>This is the only mechanism provided by the main library to help manage the
 242 resources.  The drivers are responsible to the correct behavior as defined by
 243 EGL.</p>
 244
 245 <h3><code>EGL_RENDER_BUFFER</code></h3>
 246
 247 <p>In EGL, the color buffer a context should try to render to is decided by the
 248 binding surface.  It should try to render to the front buffer if the binding
 249 surface has <code>EGL_RENDER_BUFFER</code> set to
 250 <code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
 251 surface with <code>EGL_RENDER_BUFFER</code> set to
 252 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
 253 buffer.  However, the context is allowed to make the final decision as to which
 254 color buffer it wants to or is able to render to.</p>
 255
 256 <p>For pbuffer surfaces, the render buffer is always
 257 <code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
 258 always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
 259 requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
 260 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
 261 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
 262 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
 263 pbuffer surfaces.</p>
 264
 265 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
 266 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
 267 is desirable that a driver allocates a private color buffer for each pbuffer
 268 surface created.  If the window system the driver supports has native pbuffers,
 269 or if the native pixmaps have more than one color buffers, the driver should
 270 carefully attach the native color buffers to the EGL surfaces, re-route them if
 271 required.</p>
 272
 273 <p>There is no defined behavior as to, for example, how
 274 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
 275 now, it is desired that the draw buffer in a client API be fixed for pixmap and
 276 pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
 277 client API renders to the specified render buffer for pixmap and pbuffer
 278 surfaces.</p>
 279
 280 <h3><code>EGLDisplay</code> Mutex</h3>
 281
 282 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 283 functions (well, except for GetProcAddress which does not take an
 284 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 285 not be called with the sample display at the same time.  If a driver has access
 286 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 287 should as well lock the display before using it.
 288
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