docs/egl.html

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