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>Configure your build with the desired client APIs and enable
  37 the driver for your hardware.  For example:</p>
  38
  39 <pre>
  40 $ meson configure \
  41         -D egl=true \
  42         -D gles1=true \
  43         -D gles2=true \
  44         -D dri-drivers=... \
  45         -D gallium-drivers=...
  46 </pre>
  47
  48 <p>The main library and OpenGL is enabled by default.  The first two options
  49 above enables <a href="opengles.html">OpenGL ES 1.x and 2.x</a>.  The last two
  50 options enables the listed classic and Gallium drivers respectively.</p>
  51
  52 </li>
  53
  54 <li>Build and install Mesa as usual.</li>
  55 </ol>
  56
  57 <p>In the given example, it will build and install <code>libEGL</code>,
  58 <code>libGL</code>, <code>libGLESv1_CM</code>, <code>libGLESv2</code>, and one
  59 or more EGL drivers.</p>
  60
  61 <h3>Configure Options</h3>
  62
  63 <p>There are several options that control the build of EGL at configuration
  64 time</p>
  65
  66 <dl>
  67 <dt><code>-D egl=true</code></dt>
  68 <dd>
  69
  70 <p>By default, EGL is enabled.  When disabled, the main library and the drivers
  71 will not be built.</p>
  72
  73 </dd>
  74
  75 <dt><code>-D platforms=...</code></dt>
  76 <dd>
  77
  78 <p>List the platforms (window systems) to support.  Its argument is a comma
  79 separated string such as <code>-D platforms=x11,drm</code>.  It decides
  80 the platforms a driver may support.  The first listed platform is also used by
  81 the main library to decide the native platform.</p>
  82
  83 <p>The available platforms are <code>x11</code>, <code>drm</code>,
  84 <code>wayland</code>, <code>surfaceless</code>, <code>android</code>,
  85 and <code>haiku</code>.
  86 The <code>android</code> platform can either be built as a system
  87 component, part of AOSP, using <code>Android.mk</code> files, or
  88 cross-compiled using appropriate options.
  89 The <code>haiku</code> platform can only be built with SCons.
  90 Unless for special needs, the build system should
  91 select the right platforms automatically.</p>
  92
  93 </dd>
  94
  95 <dt><code>-D gles1=true</code></dt>
  96 <dt><code>-D gles2=true</code></dt>
  97 <dd>
  98
  99 <p>These options enable OpenGL ES support in OpenGL.  The result is one big
 100 internal library that supports multiple APIs.</p>
 101
 102 </dd>
 103
 104 <dt><code>-D shared-glapi=true</code></dt>
 105 <dd>
 106
 107 <p>By default, <code>libGL</code> has its own copy of <code>libglapi</code>.
 108 This options makes <code>libGL</code> use the shared <code>libglapi</code>.  This
 109 is required if applications mix OpenGL and OpenGL ES.</p>
 110
 111 </dd>
 112
 113 </dl>
 114
 115 <h2>Use EGL</h2>
 116
 117 <h3>Demos</h3>
 118
 119 <p>There are demos for the client APIs supported by EGL.  They can be found in
 120 mesa/demos repository.</p>
 121
 122 <h3>Environment Variables</h3>
 123
 124 <p>There are several environment variables that control the behavior of EGL at
 125 runtime</p>
 126
 127 <dl>
 128 <dt><code>EGL_PLATFORM</code></dt>
 129 <dd>
 130
 131 <p>This variable specifies the native platform.  The valid values are the same
 132 as those for <code>-D platforms=...</code>.  When the variable is not set,
 133 the main library uses the first platform listed in
 134 <code>-D platforms=...</code> as the native platform.</p>
 135
 136 <p>Extensions like <code>EGL_MESA_drm_display</code> define new functions to
 137 create displays for non-native platforms.  These extensions are usually used by
 138 applications that support non-native platforms.  Setting this variable is
 139 probably required only for some of the demos found in mesa/demo repository.</p>
 140
 141 </dd>
 142
 143 <dt><code>EGL_LOG_LEVEL</code></dt>
 144 <dd>
 145
 146 <p>This changes the log level of the main library and the drivers.  The valid
 147 values are: <code>debug</code>, <code>info</code>, <code>warning</code>, and
 148 <code>fatal</code>.</p>
 149
 150 </dd>
 151 </dl>
 152
 153 <h2>EGL Drivers</h2>
 154
 155 <dl>
 156 <dt><code>egl_dri2</code></dt>
 157 <dd>
 158
 159 <p>This driver supports both <code>x11</code> and <code>drm</code> platforms.
 160 It functions as a DRI driver loader.  For <code>x11</code> support, it talks to
 161 the X server directly using (XCB-)DRI2 protocol.</p>
 162
 163 <p>This driver can share DRI drivers with <code>libGL</code>.</p>
 164
 165 </dd>
 166 </dl>
 167
 168 <h2>Packaging</h2>
 169
 170 <p>The ABI between the main library and its drivers are not stable.  Nor is
 171 there a plan to stabilize it at the moment.</p>
 172
 173 <h2>Developers</h2>
 174
 175 <p>The sources of the main library and drivers can be found at
 176 <code>src/egl/</code>.</p>
 177
 178 <h3>Lifetime of Display Resources</h3>
 179
 180 <p>Contexts and surfaces are examples of display resources.  They might live
 181 longer than the display that creates them.</p>
 182
 183 <p>In EGL, when a display is terminated through <code>eglTerminate</code>, all
 184 display resources should be destroyed.  Similarly, when a thread is released
 185 through <code>eglReleaseThread</code>, all current display resources should be
 186 released.  Another way to destroy or release resources is through functions
 187 such as <code>eglDestroySurface</code> or <code>eglMakeCurrent</code>.</p>
 188
 189 <p>When a resource that is current to some thread is destroyed, the resource
 190 should not be destroyed immediately.  EGL requires the resource to live until
 191 it is no longer current.  A driver usually calls
 192 <code>eglIs&lt;Resource&gt;Bound</code> to check if a resource is bound
 193 (current) to any thread in the destroy callbacks.  If it is still bound, the
 194 resource is not destroyed.</p>
 195
 196 <p>The main library will mark destroyed current resources as unlinked.  In a
 197 driver's <code>MakeCurrent</code> callback,
 198 <code>eglIs&lt;Resource&gt;Linked</code> can then be called to check if a newly
 199 released resource is linked to a display.  If it is not, the last reference to
 200 the resource is removed and the driver should destroy the resource.  But it
 201 should be careful here because <code>MakeCurrent</code> might be called with an
 202 uninitialized display.</p>
 203
 204 <p>This is the only mechanism provided by the main library to help manage the
 205 resources.  The drivers are responsible to the correct behavior as defined by
 206 EGL.</p>
 207
 208 <h3><code>EGL_RENDER_BUFFER</code></h3>
 209
 210 <p>In EGL, the color buffer a context should try to render to is decided by the
 211 binding surface.  It should try to render to the front buffer if the binding
 212 surface has <code>EGL_RENDER_BUFFER</code> set to
 213 <code>EGL_SINGLE_BUFFER</code>;  If the same context is later bound to a
 214 surface with <code>EGL_RENDER_BUFFER</code> set to
 215 <code>EGL_BACK_BUFFER</code>, the context should try to render to the back
 216 buffer.  However, the context is allowed to make the final decision as to which
 217 color buffer it wants to or is able to render to.</p>
 218
 219 <p>For pbuffer surfaces, the render buffer is always
 220 <code>EGL_BACK_BUFFER</code>.  And for pixmap surfaces, the render buffer is
 221 always <code>EGL_SINGLE_BUFFER</code>.  Unlike window surfaces, EGL spec
 222 requires their <code>EGL_RENDER_BUFFER</code> values to be honored.  As a
 223 result, a driver should never set <code>EGL_PIXMAP_BIT</code> or
 224 <code>EGL_PBUFFER_BIT</code> bits of a config if the contexts created with the
 225 config won't be able to honor the <code>EGL_RENDER_BUFFER</code> of pixmap or
 226 pbuffer surfaces.</p>
 227
 228 <p>It should also be noted that pixmap and pbuffer surfaces are assumed to be
 229 single-buffered, in that <code>eglSwapBuffers</code> has no effect on them.  It
 230 is desirable that a driver allocates a private color buffer for each pbuffer
 231 surface created.  If the window system the driver supports has native pbuffers,
 232 or if the native pixmaps have more than one color buffers, the driver should
 233 carefully attach the native color buffers to the EGL surfaces, re-route them if
 234 required.</p>
 235
 236 <p>There is no defined behavior as to, for example, how
 237 <code>glDrawBuffer</code> interacts with <code>EGL_RENDER_BUFFER</code>.  Right
 238 now, it is desired that the draw buffer in a client API be fixed for pixmap and
 239 pbuffer surfaces.  Therefore, the driver is responsible to guarantee that the
 240 client API renders to the specified render buffer for pixmap and pbuffer
 241 surfaces.</p>
 242
 243 <h3><code>EGLDisplay</code> Mutex</h3>
 244
 245 The <code>EGLDisplay</code> will be locked before calling any of the dispatch
 246 functions (well, except for GetProcAddress which does not take an
 247 <code>EGLDisplay</code>).  This guarantees that the same dispatch function will
 248 not be called with the sample display at the same time.  If a driver has access
 249 to an <code>EGLDisplay</code> without going through the EGL APIs, the driver
 250 should as well lock the display before using it.
 251
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