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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="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 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-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-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.</p>
  87
  88 <p>The available platforms are <code>x11</code>, <code>drm</code>,
  89 <code>wayland</code>, <code>surfaceless</code>, <code>android</code>,
  90 and <code>haiku</code>.
  91 The <code>android</code> platform can either be built as a system
  92 component, part of AOSP, using <code>Android.mk</code> files, or
  93 cross-compiled using appropriate <code>configure</code> options.
  94 The <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_PLATFORM</code></dt>
 134 <dd>
 135
 136 <p>This variable specifies the native platform.  The valid values are the same
 137 as those for <code>--with-platforms</code>.  When the variable is not set,
 138 the main library uses the first platform listed in
 139 <code>--with-platforms</code> as the native platform.</p>
 140
 141 <p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
 142 create displays for non-native platforms.  These extensions are usually used by
 143 applications that support non-native platforms.  Setting this variable is
 144 probably required only for some of the demos found in mesa/demo repository.</p>
 145
 146 </dd>
 147
 148 <dt><code>EGL_LOG_LEVEL</code></dt>
 149 <dd>
 150
 151 <p>This changes the log level of the main library and the drivers.  The valid
 152 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 153 <code>fatal</code>.</p>
 154
 155 </dd>
 156 </dl>
 157
 158 <h2>EGL Drivers</h2>
 159
 160 <dl>
 161 <dt><code>egl_dri2</code></dt>
 162 <dd>
 163
 164 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
 165 It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
 166 the X server directly using (XCB-)DRI2 protocol.</p>
 167
 168 <p>This driver can share DRI drivers with <code>libGL</code>.</p>
 169
 170 </dd>
 171
 172 <h2>Packaging</h2>
 173
 174 <p>The ABI between the main library and its drivers are not stable.  Nor is
 175 there a plan to stabilize it at the moment.</p>
 176
 177 <h2>Developers</h2>
 178
 179 <p>The sources of the main library and drivers can be found at
 180 <code>src/egl/</code>.</p>
 181
 182 <h3>Lifetime of Display Resources</h3>
 183
 184 <p>Contexts and surfaces are examples of display resources.  They might live
 185 longer than the display that creates them.</p>
 186
 187 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 188 display resources should be destroyed.  Similarly, when a thread is released
 189 through <code>eglReleaseThread</code>, all current display resources should be
 190 released.  Another way to destroy or release resources is through functions
 191 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 192
 193 <p>When a resource that is current to some thread is destroyed, the resource
 194 should not be destroyed immediately.  EGL requires the resource to live until
 195 it is no longer current.  A driver usually calls
 196 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 197 (current) to any thread in the destroy callbacks.  If it is still bound, the
 198 resource is not destroyed.</p>
 199
 200 <p>The main library will mark destroyed current resources as unlinked.  In a
 201 driver's <code>MakeCurrent</code> callback,
 202 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 203 released resource is linked to a display.  If it is not, the last reference to
 204 the resource is removed and the driver should destroy the resource.  But it
 205 should be careful here because <code>MakeCurrent</code> might be called with an
 206 uninitialized display.</p>
 207
 208 <p>This is the only mechanism provided by the main library to help manage the
 209 resources.  The drivers are responsible to the correct behavior as defined by
 210 EGL.</p>
 211
 212 <h3><code>EGL_RENDER_BUFFER</code></h3>
 213
 214 <p>In EGL, the color buffer a context should try to render to is decided by the
 215 binding surface.  It should try to render to the front buffer if the binding
 216 surface has <code>EGL_RENDER_BUFFER</code> set to
 217 <code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
 218 surface with <code>EGL_RENDER_BUFFER</code> set to
 219 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
 220 buffer.  However, the context is allowed to make the final decision as to which
 221 color buffer it wants to or is able to render to.</p>
 222
 223 <p>For pbuffer surfaces, the render buffer is always
 224 <code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
 225 always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
 226 requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
 227 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
 228 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
 229 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
 230 pbuffer surfaces.</p>
 231
 232 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
 233 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
 234 is desirable that a driver allocates a private color buffer for each pbuffer
 235 surface created.  If the window system the driver supports has native pbuffers,
 236 or if the native pixmaps have more than one color buffers, the driver should
 237 carefully attach the native color buffers to the EGL surfaces, re-route them if
 238 required.</p>
 239
 240 <p>There is no defined behavior as to, for example, how
 241 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
 242 now, it is desired that the draw buffer in a client API be fixed for pixmap and
 243 pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
 244 client API renders to the specified render buffer for pixmap and pbuffer
 245 surfaces.</p>
 246
 247 <h3><code>EGLDisplay</code> Mutex</h3>
 248
 249 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 250 functions (well, except for GetProcAddress which does not take an
 251 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 252 not be called with the sample display at the same time.  If a driver has access
 253 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 254 should as well lock the display before using it.
 255
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