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 forces the specified EGL driver to be loaded.  It comes in
 132 handy when one wants to test a specific driver.</p>
 133
 134 </li>
 135
 136 <li><code>EGL_DISPLAY</code>
 137
 138 <p>When <code>EGL_DRIVER</code> is not set, the main library loads <em>all</em>
 139 EGL drivers that support a certain window system.  <code>EGL_DISPLAY</code> can
 140 be used to specify the window system and the valid values are, for example,
 141 <code>x11</code> or <code>kms</code>.  When the variable is not set, the main
 142 library defaults the value to the first window system listed in
 143 <code>--with-egl-displays</code> at configuration time.
 144
 145 </li>
 146
 147 <li><code>EGL_LOG_LEVEL</code>
 148
 149 <p>This changes the log level of the main library and the drivers.  The valid
 150 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 151 <code>fatal</code>.</p>
 152
 153 </li>
 154
 155 <li><code>EGL_SOFTWARE</code>
 156
 157 <p>For drivers that support both hardware and software rendering, setting this
 158 variable to true forces the use of software rendering.</p>
 159
 160 </li>
 161 </ul>
 162
 163 <h2>EGL Drivers</h2>
 164
 165 <p>There are two categories of EGL drivers: Gallium and classic.</p>
 166
 167 <p>Gallium EGL drivers supports all rendering APIs specified in EGL 1.4.  The
 168 support for optional EGL functions and EGL extensions is usually more complete
 169 than the classic ones.  These drivers depend on the <code>egl</code> state
 170 tracker to build.  The available drivers are</p>
 171
 172 <ul>
 173 <li><code>egl_&lt;dpy&gt;_i915</code></li>
 174 <li><code>egl_&lt;dpy&gt;_i965</code></li>
 175 <li><code>egl_&lt;dpy&gt;_radeon</code></li>
 176 <li><code>egl_&lt;dpy&gt;_nouveau</code></li>
 177 <li><code>egl_&lt;dpy&gt;_swrast</code></li>
 178 <li><code>egl_&lt;dpy&gt;_vmwgfx</code></li>
 179 </ul>
 180
 181 <p><code>&lt;dpy&gt;</code> is given by <code>--with-egl-displays</code> at
 182 configuration time.  There will be one EGL driver for each combination of the
 183 displays listed and the hardware drivers enabled.</p>
 184
 185 <p>Classic EGL drivers, on the other hand, supports only OpenGL as its
 186 rendering API.  They can be found under <code>src/egl/drivers/</code>.  There
 187 are 3 of them</p>
 188
 189 <ul>
 190 <li><code>egl_glx</code>
 191
 192 <p>This driver provides a wrapper to GLX.  It uses exclusively GLX to implement
 193 the EGL API.  It supports both direct and indirect rendering when the GLX does.
 194 It is accelerated when the GLX is.  As such, it cannot provide functions that
 195 is not available in GLX or GLX extensions.</p>
 196 </li>
 197
 198 <li><code>egl_xdri</code>
 199
 200 <p>This driver supports the X Window System as its window system.  It functions
 201 as a DRI driver loader and can load DRI/DRI2/DRISW drivers.  Unlike
 202 <code>egl_glx</code>, it has no dependency on <code>libGL</code>.  It talks to
 203 the X server directly using DRI or DRI2 protocols.  It also talks minimal GLX
 204 protocol for things like available visuals or fbconfigs.  With direct access to
 205 the DRI drivers, it has the potential to support more EGL functions that are
 206 not possible with <code>egl_glx</code>.</p>
 207
 208 </li>
 209 <li><code>egl_dri</code>
 210
 211 <p>This driver lacks maintenance and does <em>not</em> build.  It is similiar
 212 to <code>egl_xdri</code> in that it functions as a DRI driver loader.  But
 213 unlike <code>egl_xdri</code>, it supports Linux framebuffer devices as its
 214 window system and supports EGL_MESA_screen_surface extension.  It loads only
 215 DRI1 drivers.  As DRI1 drivers is phasing out, it might be better to rewrite
 216 the driver to support KMS and DRI2.</p>
 217
 218 </li>
 219 </ul>
 220
 221 <p>To use the classic drivers, one must manually set <code>EGL_DRIVER</code> at
 222 runtime.</p>
 223
 224 <h2>Developers</h2>
 225
 226 <p>The sources of the main library and the classic drivers can be found at
 227 <code>src/egl/</code>.  The sources of the <code>egl</code> state tracker can
 228 be found at <code>src/gallium/state_trackers/egl/</code>.</p>
 229
 230 <p>The suggested way to learn to write a EGL driver is to see how other drivers
 231 are written.  <code>egl_glx</code> should be a good reference.  It works in any
 232 environment that has GLX support, and it is simpler than most drivers.</p>
 233
 234 <h3>Lifetime of Display Resources</h3>
 235
 236 <p>Contexts and surfaces are examples of display resources.  They might live
 237 longer than the display that creates them.</p>
 238
 239 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 240 display resources should be destroyed.  Similarly, when a thread is released
 241 throught <code>eglReleaseThread</code>, all current display resources should be
 242 released.  Another way to destory or release resources is through functions
 243 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 244
 245 <p>When a resource that is current to some thread is destroyed, the resource
 246 should not be destroyed immediately.  EGL requires the resource to live until
 247 it is no longer current.  A driver usually calls
 248 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 249 (current) to any thread in the destroy callbacks.  If it is still bound, the
 250 resource is not destroyed.</p>
 251
 252 <p>The main library will mark destroyed current resources as unlinked.  In a
 253 driver's <code>MakeCurrent</code> callback,
 254 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 255 released resource is linked to a display.  If it is not, the last reference to
 256 the resource is removed and the driver should destroy the resource.  But it
 257 should be careful here because <code>MakeCurrent</code> might be called with an
 258 uninitialized display.</p>
 259
 260 <p>This is the only mechanism provided by the main library to help manage the
 261 resources.  The drivers are responsible to the correct behavior as defined by
 262 EGL.</p>
 263
 264 <h3>TODOs</h3>
 265
 266 <ul>
 267 <li>Thread safety</li>
 268 <li>Pass the conformance tests</li>
 269 <li>Better automatic driver selection: <code>EGL_DISPLAY</code> loads all
 270 drivers and might eat too much memory.</li>
 271 <li>Stop using <code>glxinit.c</code> and sources from <code>src/glx/x11/</code></li>
 272
 273 </ul>
 274
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