docs/egl.html

   1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
   2 <html lang="en">
   3 <head>
   4   <meta http-equiv="content-type" content="text/html; charset=utf-8">
   5   <title>Mesa EGL</title>
   6   <link rel="stylesheet" type="text/css" href="mesa.css">
   7 </head>
   8 <body>
   9
  10 <div class="header">
  11   <h1>The Mesa 3D Graphics Library</h1>
  12 </div>
  13
  14 <iframe src="contents.html"></iframe>
  15 <div class="content">
  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="http://www.khronos.org/egl/" target="_parent">
  22 http://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 <ul>
  64 <li><code>--enable-egl</code>
  65
  66 <p>By default, EGL is enabled.  When disabled, the main library and the drivers
  67 will not be built.</p>
  68
  69 </li>
  70
  71 <li><code>--with-egl-driver-dir</code>
  72
  73 <p>The directory EGL drivers should be installed to.  If not specified, EGL
  74 drivers will be installed to <code>${libdir}/egl</code>.</p>
  75
  76 </li>
  77
  78 <li><code>--enable-gallium-egl</code>
  79
  80 <p>Enable the optional <code>egl_gallium</code> driver.</p>
  81
  82 </li>
  83
  84 <li><code>--with-egl-platforms</code>
  85
  86 <p>List the platforms (window systems) to support.  Its argument is a comma
  87 seprated string such as <code>--with-egl-platforms=x11,drm</code>.  It decides
  88 the platforms a driver may support.  The first listed platform is also used by
  89 the main library to decide the native platform: the platform the EGL native
  90 types such as <code>EGLNativeDisplayType</code> or
  91 <code>EGLNativeWindowType</code> defined for.</p>
  92
  93 <p>The available platforms are <code>x11</code>, <code>drm</code>,
  94 <code>fbdev</code>, and <code>gdi</code>.  The <code>gdi</code> platform can
  95 only be built with SCons.  Unless for special needs, the build system should
  96 select the right platforms automatically.</p>
  97
  98 </li>
  99
 100 <li><code>--enable-gles1</code> and <code>--enable-gles2</code>
 101
 102 <p>These options enable OpenGL ES support in OpenGL.  The result is one big
 103 internal library that supports multiple APIs.</p>
 104
 105 </li>
 106
 107 <li><code>--enable-shared-glapi</code>
 108
 109 <p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
 110 This options makes <code>libGL</code> use the shared <code>libglapi</code>.  This
 111 is required if applications mix OpenGL and OpenGL ES.</p>
 112
 113 </li>
 114
 115 <li><code>--enable-openvg</code>
 116
 117 <p>OpenVG must be explicitly enabled by this option.</p>
 118
 119 </li>
 120
 121 </ul>
 122
 123 <h2>Use EGL</h2>
 124
 125 <h3>Demos</h3>
 126
 127 <p>There are demos for the client APIs supported by EGL.  They can be found in
 128 mesa/demos repository.</p>
 129
 130 <h3>Environment Variables</h3>
 131
 132 <p>There are several environment variables that control the behavior of EGL at
 133 runtime</p>
 134
 135 <ul>
 136 <li><code>EGL_DRIVERS_PATH</code>
 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 </li>
 155
 156 <li><code>EGL_DRIVER</code>
 157
 158 <p>This variable specifies a full path to or the name of an EGL driver.  It
 159 forces the specified EGL driver to be loaded.  It comes in handy when one wants
 160 to test a specific driver.  This variable is ignored for setuid/setgid
 161 binaries.</p>
 162
 163 </li>
 164
 165 <li><code>EGL_PLATFORM</code>
 166
 167 <p>This variable specifies the native platform.  The valid values are the same
 168 as those for <code>--with-egl-platforms</code>.  When the variable is not set,
 169 the main library uses the first platform listed in
 170 <code>--with-egl-platforms</code> as the native platform.</p>
 171
 172 <p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
 173 create displays for non-native platforms.  These extensions are usually used by
 174 applications that support non-native platforms.  Setting this variable is
 175 probably required only for some of the demos found in mesa/demo repository.</p>
 176
 177 </li>
 178
 179 <li><code>EGL_LOG_LEVEL</code>
 180
 181 <p>This changes the log level of the main library and the drivers.  The valid
 182 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 183 <code>fatal</code>.</p>
 184
 185 </li>
 186
 187 <li><code>EGL_SOFTWARE</code>
 188
 189 <p>For drivers that support both hardware and software rendering, setting this
 190 variable to true forces the use of software rendering.</p>
 191
 192 </li>
 193 </ul>
 194
 195 <h2>EGL Drivers</h2>
 196
 197 <ul>
 198 <li><code>egl_dri2</code>
 199
 200 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
 201 It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
 202 the X server directly using (XCB-)DRI2 protocol.</p>
 203
 204 <p>This driver can share DRI drivers with <code>libGL</code>.</p>
 205
 206 </li>
 207
 208 <li><code>egl_gallium</code>
 209
 210 <p>This driver is based on Gallium3D.  It supports all rendering APIs and
 211 hardwares supported by Gallium3D.  It is the only driver that supports OpenVG.
 212 The supported platforms are X11, DRM, FBDEV, and GDI.</p>
 213
 214 <p>This driver comes with its own hardware drivers
 215 (<code>pipe_&lt;hw&gt;</code>) and client API modules
 216 (<code>st_&lt;api&gt;</code>).</p>
 217
 218 </li>
 219
 220 <li><code>egl_glx</code>
 221
 222 <p>This driver provides a wrapper to GLX.  It uses exclusively GLX to implement
 223 the EGL API.  It supports both direct and indirect rendering when the GLX does.
 224 It is accelerated when the GLX is.  As such, it cannot provide functions that
 225 is not available in GLX or GLX extensions.</p>
 226 </li>
 227 </ul>
 228
 229 <h2>Packaging</h2>
 230
 231 <p>The ABI between the main library and its drivers are not stable.  Nor is
 232 there a plan to stabilize it at the moment.  Of the EGL drivers,
 233 <code>egl_gallium</code> has its own hardware drivers and client API modules.
 234 They are considered internal to <code>egl_gallium</code> and there is also no
 235 stable ABI between them.  These should be kept in mind when packaging for
 236 distribution.</p>
 237
 238 <p>Generally, <code>egl_dri2</code> is preferred over <code>egl_gallium</code>
 239 when the system already has DRI drivers.  As <code>egl_gallium</code> is loaded
 240 before <code>egl_dri2</code> when both are available, <code>egl_gallium</code>
 241 is disabled by default.</p>
 242
 243 <h2>Developers</h2>
 244
 245 <p>The sources of the main library and the classic drivers can be found at
 246 <code>src/egl/</code>.  The sources of the <code>egl</code> state tracker can
 247 be found at <code>src/gallium/state_trackers/egl/</code>.</p>
 248
 249 <p>The suggested way to learn to write a EGL driver is to see how other drivers
 250 are written.  <code>egl_glx</code> should be a good reference.  It works in any
 251 environment that has GLX support, and it is simpler than most drivers.</p>
 252
 253 <h3>Lifetime of Display Resources</h3>
 254
 255 <p>Contexts and surfaces are examples of display resources.  They might live
 256 longer than the display that creates them.</p>
 257
 258 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 259 display resources should be destroyed.  Similarly, when a thread is released
 260 throught <code>eglReleaseThread</code>, all current display resources should be
 261 released.  Another way to destory or release resources is through functions
 262 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 263
 264 <p>When a resource that is current to some thread is destroyed, the resource
 265 should not be destroyed immediately.  EGL requires the resource to live until
 266 it is no longer current.  A driver usually calls
 267 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 268 (current) to any thread in the destroy callbacks.  If it is still bound, the
 269 resource is not destroyed.</p>
 270
 271 <p>The main library will mark destroyed current resources as unlinked.  In a
 272 driver's <code>MakeCurrent</code> callback,
 273 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 274 released resource is linked to a display.  If it is not, the last reference to
 275 the resource is removed and the driver should destroy the resource.  But it
 276 should be careful here because <code>MakeCurrent</code> might be called with an
 277 uninitialized display.</p>
 278
 279 <p>This is the only mechanism provided by the main library to help manage the
 280 resources.  The drivers are responsible to the correct behavior as defined by
 281 EGL.</p>
 282
 283 <h3><code>EGL_RENDER_BUFFER</code></h3>
 284
 285 <p>In EGL, the color buffer a context should try to render to is decided by the
 286 binding surface.  It should try to render to the front buffer if the binding
 287 surface has <code>EGL_RENDER_BUFFER</code> set to
 288 <code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
 289 surface with <code>EGL_RENDER_BUFFER</code> set to
 290 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
 291 buffer.  However, the context is allowed to make the final decision as to which
 292 color buffer it wants to or is able to render to.</p>
 293
 294 <p>For pbuffer surfaces, the render buffer is always
 295 <code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
 296 always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
 297 requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
 298 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
 299 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
 300 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
 301 pbuffer surfaces.</p>
 302
 303 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
 304 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
 305 is desirable that a driver allocates a private color buffer for each pbuffer
 306 surface created.  If the window system the driver supports has native pbuffers,
 307 or if the native pixmaps have more than one color buffers, the driver should
 308 carefully attach the native color buffers to the EGL surfaces, re-route them if
 309 required.</p>
 310
 311 <p>There is no defined behavior as to, for example, how
 312 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
 313 now, it is desired that the draw buffer in a client API be fixed for pixmap and
 314 pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
 315 client API renders to the specified render buffer for pixmap and pbuffer
 316 surfaces.</p>
 317
 318 <h3><code>EGLDisplay</code> Mutex</h3>
 319
 320 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 321 functions (well, except for GetProcAddress which does not take an
 322 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 323 not be called with the sample display at the same time.  If a driver has access
 324 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 325 should as well lock the display before using it.
 326
 327 </div>
 328 </body>
 329 </html>