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="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 </dl>
 172
 173 <h2>Packaging</h2>
 174
 175 <p>The ABI between the main library and its drivers are not stable.  Nor is
 176 there a plan to stabilize it at the moment.</p>
 177
 178 <h2>Developers</h2>
 179
 180 <p>The sources of the main library and drivers can be found at
 181 <code>src/egl/</code>.</p>
 182
 183 <h3>Lifetime of Display Resources</h3>
 184
 185 <p>Contexts and surfaces are examples of display resources.  They might live
 186 longer than the display that creates them.</p>
 187
 188 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 189 display resources should be destroyed.  Similarly, when a thread is released
 190 through <code>eglReleaseThread</code>, all current display resources should be
 191 released.  Another way to destroy or release resources is through functions
 192 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 193
 194 <p>When a resource that is current to some thread is destroyed, the resource
 195 should not be destroyed immediately.  EGL requires the resource to live until
 196 it is no longer current.  A driver usually calls
 197 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 198 (current) to any thread in the destroy callbacks.  If it is still bound, the
 199 resource is not destroyed.</p>
 200
 201 <p>The main library will mark destroyed current resources as unlinked.  In a
 202 driver's <code>MakeCurrent</code> callback,
 203 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 204 released resource is linked to a display.  If it is not, the last reference to
 205 the resource is removed and the driver should destroy the resource.  But it
 206 should be careful here because <code>MakeCurrent</code> might be called with an
 207 uninitialized display.</p>
 208
 209 <p>This is the only mechanism provided by the main library to help manage the
 210 resources.  The drivers are responsible to the correct behavior as defined by
 211 EGL.</p>
 212
 213 <h3><code>EGL_RENDER_BUFFER</code></h3>
 214
 215 <p>In EGL, the color buffer a context should try to render to is decided by the
 216 binding surface.  It should try to render to the front buffer if the binding
 217 surface has <code>EGL_RENDER_BUFFER</code> set to
 218 <code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
 219 surface with <code>EGL_RENDER_BUFFER</code> set to
 220 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
 221 buffer.  However, the context is allowed to make the final decision as to which
 222 color buffer it wants to or is able to render to.</p>
 223
 224 <p>For pbuffer surfaces, the render buffer is always
 225 <code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
 226 always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
 227 requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
 228 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
 229 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
 230 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
 231 pbuffer surfaces.</p>
 232
 233 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
 234 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
 235 is desirable that a driver allocates a private color buffer for each pbuffer
 236 surface created.  If the window system the driver supports has native pbuffers,
 237 or if the native pixmaps have more than one color buffers, the driver should
 238 carefully attach the native color buffers to the EGL surfaces, re-route them if
 239 required.</p>
 240
 241 <p>There is no defined behavior as to, for example, how
 242 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
 243 now, it is desired that the draw buffer in a client API be fixed for pixmap and
 244 pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
 245 client API renders to the specified render buffer for pixmap and pbuffer
 246 surfaces.</p>
 247
 248 <h3><code>EGLDisplay</code> Mutex</h3>
 249
 250 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 251 functions (well, except for GetProcAddress which does not take an
 252 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 253 not be called with the sample display at the same time.  If a driver has access
 254 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 255 should as well lock the display before using it.
 256
 257 </div>
 258 </body>
 259 </html>