docs/egl.html

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   9 <h1>Mesa EGL</h1>
  10
  11 <p>The current version of EGL in Mesa implements EGL 1.4.  More information
  12 about EGL can be found at
  13 <a href="http://www.khronos.org/egl/" target="_parent">
  14 http://www.khronos.org/egl/</a>.</p>
  15
  16 <p>The Mesa's implementation of EGL uses a driver architecture.  The main
  17 library (<code>libEGL</code>) is window system neutral.  It provides the EGL
  18 API entry points and helper functions for use by the drivers.  Drivers are
  19 dynamically loaded by the main library and most of the EGL API calls are
  20 directly dispatched to the drivers.</p>
  21
  22 <p>The driver in use decides the window system to support.  For drivers that
  23 support hardware rendering, there are usually multiple drivers supporting the
  24 same window system.  Each one of of them supports a certain range of graphics
  25 cards.</p>
  26
  27 <h2>Build EGL</h2>
  28
  29 <ol>
  30 <li>
  31 <p>Run <code>configure</code> with the desired state trackers and and enable
  32 the Gallium driver for your hardware.  For example</p>
  33
  34 <pre>
  35   $ ./configure --with-state-trackers=egl,es,vega --enable-gallium-{swrast,intel}
  36 </pre>
  37
  38 <p>The main library will be enabled by default.  The <code>egl</code> state
  39 tracker is needed by a number of EGL drivers.  EGL drivers will be covered
  40 later.  The <a href="opengles.html">es state tracker</a> provides OpenGL ES 1.x
  41 and 2.x and the <a href="openvg.html">vega state tracker</a> provides OpenVG
  42 1.x.</p>
  43 </li>
  44
  45 <li>Build and install Mesa as usual.</li>
  46 </ol>
  47
  48 <p>In the given example, it will build and install <code>libEGL</code>,
  49 <code>libGLESv1_CM</code>, <code>libGLESv2</code>, <code>libOpenVG</code>, and
  50 one or more EGL drivers.</p>
  51
  52 <h3>Configure Options</h3>
  53
  54 <p>There are several options that control the build of EGL at configuration
  55 time</p>
  56
  57 <ul>
  58 <li><code>--enable-egl</code>
  59
  60 <p>By default, EGL is enabled.  When disabled, the main library and the drivers
  61 will not be built.</p>
  62
  63 </li>
  64
  65 <li><code>--with-egl-driver-dir</code>
  66
  67 <p>The directory EGL drivers should be installed to.  If not specified, EGL
  68 drivers will be installed to <code>${libdir}/egl</code>.</p>
  69
  70 </li>
  71
  72 <li><code>--with-egl-displays</code>
  73
  74 <p>List the window system(s) to support.  It is by default <code>x11</code>,
  75 which supports the X Window System.  Its argument is a comma separated string
  76 like, for example, <code>--with-egl-displays=x11,kms</code>.  Because an EGL
  77 driver decides which window system to support, this example will enable two
  78 (sets of) EGL drivers.  One supports the X window system and the other supports
  79 bare KMS (kernel modesetting).</p>
  80
  81 </li>
  82
  83 <li><code>--with-state-trackers</code>
  84
  85 <p>The argument is a comma separated string.  It is usually used to specify the
  86 rendering APIs, like OpenGL ES or OpenVG, to build.  But it should be noted
  87 that a number of EGL drivers depend on the <code>egl</code> state tracker.
  88 They will <em>not</em> be built without the <code>egl</code> state tracker.</p>
  89
  90 </li>
  91
  92 <li><code>--enable-gallium-swrast</code>
  93
  94 <p>This option is not specific to EGL.  But if there is no driver for your
  95 hardware, or you are experiencing problems with the hardware driver, you can
  96 enable the swrast DRM driver.  It is a dummy driver and EGL will fallback to
  97 software rendering automatically.</p>
  98
  99 </li>
 100 </ul>
 101
 102 <h3>OpenGL</h3>
 103
 104 <p>The OpenGL state tracker is not built in the above example.  It should be
 105 noted that the classic <code>libGL</code> is not a state tracker and cannot be
 106 used with EGL (unless the EGL driver in use is <code>egl_glx</code>).  To build
 107 the OpenGL state tracker, one may append <code>glx</code> to
 108 <code>--with-state-trackers</code> and manually build
 109 <code>src/gallium/winsys/xlib/</code>.</p>
 110
 111 <h2>Use EGL</h2>
 112
 113 <p> The demos for OpenGL ES and OpenVG can be found in <code>progs/es1/</code>,
 114 <code>progs/es2/</code> and <code>progs/openvg/</code>.  You can use them to
 115 test your build.  For example,</p>
 116
 117 <pre>
 118   $ cd progs/es1/xegl
 119   $ make
 120   $ ./torus
 121 </pre>
 122
 123 <h3>Environment Variables</h3>
 124
 125 <p>There are several environment variables that control the behavior of EGL at
 126 runtime</p>
 127
 128 <ul>
 129 <li><code>EGL_DRIVER</code>
 130
 131 <p>This variable specifies a full path to an EGL driver and it forces the
 132 specified EGL driver to be loaded.  It comes in handy when one wants to test a
 133 specific driver.</p>
 134
 135 </li>
 136
 137 <li><code>EGL_DISPLAY</code>
 138
 139 <p>When <code>EGL_DRIVER</code> is not set, the main library loads <em>all</em>
 140 EGL drivers that support a certain window system.  <code>EGL_DISPLAY</code> can
 141 be used to specify the window system and the valid values are, for example,
 142 <code>x11</code> or <code>kms</code>.  When the variable is not set, the main
 143 library defaults the value to the first window system listed in
 144 <code>--with-egl-displays</code> at configuration time.
 145
 146 </li>
 147
 148 <li><code>EGL_LOG_LEVEL</code>
 149
 150 <p>This changes the log level of the main library and the drivers.  The valid
 151 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 152 <code>fatal</code>.</p>
 153
 154 </li>
 155
 156 <li><code>EGL_SOFTWARE</code>
 157
 158 <p>For drivers that support both hardware and software rendering, setting this
 159 variable to true forces the use of software rendering.</p>
 160
 161 </li>
 162 </ul>
 163
 164 <h2>EGL Drivers</h2>
 165
 166 <p>There are two categories of EGL drivers: Gallium and classic.</p>
 167
 168 <p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4.  The
 169 support for optional EGL functions and EGL extensions is usually more complete
 170 than the classic ones.  These drivers depend on the <code>egl</code> state
 171 tracker to build.  The available drivers are</p>
 172
 173 <ul>
 174 <li><code>egl_&lt;dpy&gt;_i915</code></li>
 175 <li><code>egl_&lt;dpy&gt;_i965</code></li>
 176 <li><code>egl_&lt;dpy&gt;_radeon</code></li>
 177 <li><code>egl_&lt;dpy&gt;_nouveau</code></li>
 178 <li><code>egl_&lt;dpy&gt;_swrast</code></li>
 179 <li><code>egl_&lt;dpy&gt;_vmwgfx</code></li>
 180 </ul>
 181
 182 <p><code>&lt;dpy&gt;</code> is given by <code>--with-egl-displays</code> at
 183 configuration time.  There will be one EGL driver for each combination of the
 184 displays listed and the hardware drivers enabled.</p>
 185
 186 <p>Classic EGL drivers, on the other hand, supports only OpenGL as its
 187 rendering API.  They can be found under <code>src/egl/drivers/</code>.  There
 188 are 3 of them</p>
 189
 190 <ul>
 191 <li><code>egl_glx</code>
 192
 193 <p>This driver provides a wrapper to GLX.  It uses exclusively GLX to implement
 194 the EGL API.  It supports both direct and indirect rendering when the GLX does.
 195 It is accelerated when the GLX is.  As such, it cannot provide functions that
 196 is not available in GLX or GLX extensions.</p>
 197 </li>
 198
 199 <li><code>egl_xdri</code>
 200
 201 <p>This driver supports the X Window System as its window system.  It functions
 202 as a DRI driver loader and can load DRI/DRI2/DRISW drivers.  Unlike
 203 <code>egl_glx</code>, it has no dependency on <code>libGL</code>.  It talks to
 204 the X server directly using DRI or DRI2 protocols.  It also talks minimal GLX
 205 protocol for things like available visuals or fbconfigs.  With direct access to
 206 the DRI drivers, it has the potential to support more EGL functions that are
 207 not possible with <code>egl_glx</code>.</p>
 208
 209 </li>
 210 <li><code>egl_dri</code>
 211
 212 <p>This driver lacks maintenance and does <em>not</em> build.  It is similiar
 213 to <code>egl_xdri</code> in that it functions as a DRI driver loader.  But
 214 unlike <code>egl_xdri</code>, it supports Linux framebuffer devices as its
 215 window system and supports EGL_MESA_screen_surface extension.  It loads only
 216 DRI1 drivers.  As DRI1 drivers is phasing out, it might be better to rewrite
 217 the driver to support KMS and DRI2.</p>
 218
 219 </li>
 220 </ul>
 221
 222 <p>To use the classic drivers, one must manually set <code>EGL_DRIVER</code> at
 223 runtime.</p>
 224
 225 <h2>Developers</h2>
 226
 227 <p>The sources of the main library and the classic drivers can be found at
 228 <code>src/egl/</code>.  The sources of the <code>egl</code> state tracker can
 229 be found at <code>src/gallium/state_trackers/egl/</code>.</p>
 230
 231 <p>The suggested way to learn to write a EGL driver is to see how other drivers
 232 are written.  <code>egl_glx</code> should be a good reference.  It works in any
 233 environment that has GLX support, and it is simpler than most drivers.</p>
 234
 235 <h3>Lifetime of Display Resources</h3>
 236
 237 <p>Contexts and surfaces are examples of display resources.  They might live
 238 longer than the display that creates them.</p>
 239
 240 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 241 display resources should be destroyed.  Similarly, when a thread is released
 242 throught <code>eglReleaseThread</code>, all current display resources should be
 243 released.  Another way to destory or release resources is through functions
 244 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 245
 246 <p>When a resource that is current to some thread is destroyed, the resource
 247 should not be destroyed immediately.  EGL requires the resource to live until
 248 it is no longer current.  A driver usually calls
 249 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 250 (current) to any thread in the destroy callbacks.  If it is still bound, the
 251 resource is not destroyed.</p>
 252
 253 <p>The main library will mark destroyed current resources as unlinked.  In a
 254 driver's <code>MakeCurrent</code> callback,
 255 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 256 released resource is linked to a display.  If it is not, the last reference to
 257 the resource is removed and the driver should destroy the resource.  But it
 258 should be careful here because <code>MakeCurrent</code> might be called with an
 259 uninitialized display.</p>
 260
 261 <p>This is the only mechanism provided by the main library to help manage the
 262 resources.  The drivers are responsible to the correct behavior as defined by
 263 EGL.</p>
 264
 265 <h3>TODOs</h3>
 266
 267 <ul>
 268 <li>Thread safety</li>
 269 <li>Pass the conformance tests</li>
 270 <li>Better automatic driver selection: <code>EGL_DISPLAY</code> loads all
 271 drivers and might eat too much memory.</li>
 272 <li>Stop using <code>glxinit.c</code> and sources from <code>src/glx/x11/</code></li>
 273
 274 </ul>
 275
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