docs/egl.rst

   1 EGL
   2 ===
   3
   4 The current version of EGL in Mesa implements EGL 1.4. More information
   5 about EGL can be found at https://www.khronos.org/egl/.
   6
   7 The Mesa's implementation of EGL uses a driver architecture. The main
   8 library (``libEGL``) is window system neutral. It provides the EGL API
   9 entry points and helper functions for use by the drivers. Drivers are
  10 dynamically loaded by the main library and most of the EGL API calls are
  11 directly dispatched to the drivers.
  12
  13 The driver in use decides the window system to support.
  14
  15 Build EGL
  16 ---------
  17
  18 #. Configure your build with the desired client APIs and enable the
  19    driver for your hardware. For example:
  20
  21    .. code-block:: console
  22
  23       $ meson configure \
  24               -D egl=true \
  25               -D gles1=true \
  26               -D gles2=true \
  27               -D dri-drivers=... \
  28               -D gallium-drivers=...
  29
  30    The main library and OpenGL is enabled by default. The first two
  31    options above enables :doc:`OpenGL ES 1.x and 2.x <opengles>`. The
  32    last two options enables the listed classic and Gallium drivers
  33    respectively.
  34
  35 #. Build and install Mesa as usual.
  36
  37 In the given example, it will build and install ``libEGL``, ``libGL``,
  38 ``libGLESv1_CM``, ``libGLESv2``, and one or more EGL drivers.
  39
  40 Configure Options
  41 ~~~~~~~~~~~~~~~~~
  42
  43 There are several options that control the build of EGL at configuration
  44 time
  45
  46 ``-D egl=true``
  47    By default, EGL is enabled. When disabled, the main library and the
  48    drivers will not be built.
  49
  50 ``-D platforms=...``
  51    List the platforms (window systems) to support. Its argument is a
  52    comma separated string such as ``-D platforms=x11,drm``. It decides
  53    the platforms a driver may support. The first listed platform is also
  54    used by the main library to decide the native platform.
  55
  56    The available platforms are ``x11``, ``drm``, ``wayland``,
  57    ``surfaceless``, ``android``, and ``haiku``. The ``android`` platform
  58    can either be built as a system component, part of AOSP, using
  59    ``Android.mk`` files, or cross-compiled using appropriate options.
  60    Unless for special needs, the build system should select the right
  61    platforms automatically.
  62
  63 ``-D gles1=true`` and ``-D gles2=true``
  64    These options enable OpenGL ES support in OpenGL. The result is one
  65    big internal library that supports multiple APIs.
  66
  67 ``-D shared-glapi=true``
  68    By default, ``libGL`` has its own copy of ``libglapi``. This options
  69    makes ``libGL`` use the shared ``libglapi``. This is required if
  70    applications mix OpenGL and OpenGL ES.
  71
  72 Use EGL
  73 -------
  74
  75 Demos
  76 ~~~~~
  77
  78 There are demos for the client APIs supported by EGL. They can be found
  79 in mesa/demos repository.
  80
  81 Environment Variables
  82 ~~~~~~~~~~~~~~~~~~~~~
  83
  84 There are several environment variables that control the behavior of EGL
  85 at runtime
  86
  87 ``EGL_PLATFORM``
  88    This variable specifies the native platform. The valid values are the
  89    same as those for ``-D platforms=...``. When the variable is not set,
  90    the main library uses the first platform listed in
  91    ``-D platforms=...`` as the native platform.
  92
  93    Extensions like ``EGL_MESA_drm_display`` define new functions to
  94    create displays for non-native platforms. These extensions are
  95    usually used by applications that support non-native platforms.
  96    Setting this variable is probably required only for some of the demos
  97    found in mesa/demo repository.
  98
  99 ``EGL_LOG_LEVEL``
 100    This changes the log level of the main library and the drivers. The
 101    valid values are: ``debug``, ``info``, ``warning``, and ``fatal``.
 102
 103 EGL Drivers
 104 -----------
 105
 106 ``egl_dri2``
 107    This driver supports both ``x11`` and ``drm`` platforms. It functions
 108    as a DRI driver loader. For ``x11`` support, it talks to the X server
 109    directly using (XCB-)DRI2 protocol.
 110
 111    This driver can share DRI drivers with ``libGL``.
 112
 113 Packaging
 114 ---------
 115
 116 The ABI between the main library and its drivers are not stable. Nor is
 117 there a plan to stabilize it at the moment.
 118
 119 Developers
 120 ----------
 121
 122 The sources of the main library and drivers can be found at
 123 ``src/egl/``.
 124
 125 Lifetime of Display Resources
 126 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 127
 128 Contexts and surfaces are examples of display resources. They might live
 129 longer than the display that creates them.
 130
 131 In EGL, when a display is terminated through ``eglTerminate``, all
 132 display resources should be destroyed. Similarly, when a thread is
 133 released through ``eglReleaseThread``, all current display resources
 134 should be released. Another way to destroy or release resources is
 135 through functions such as ``eglDestroySurface`` or ``eglMakeCurrent``.
 136
 137 When a resource that is current to some thread is destroyed, the
 138 resource should not be destroyed immediately. EGL requires the resource
 139 to live until it is no longer current. A driver usually calls
 140 ``eglIs<Resource>Bound`` to check if a resource is bound (current) to
 141 any thread in the destroy callbacks. If it is still bound, the resource
 142 is not destroyed.
 143
 144 The main library will mark destroyed current resources as unlinked. In a
 145 driver's ``MakeCurrent`` callback, ``eglIs<Resource>Linked`` can then be
 146 called to check if a newly released resource is linked to a display. If
 147 it is not, the last reference to the resource is removed and the driver
 148 should destroy the resource. But it should be careful here because
 149 ``MakeCurrent`` might be called with an uninitialized display.
 150
 151 This is the only mechanism provided by the main library to help manage
 152 the resources. The drivers are responsible to the correct behavior as
 153 defined by EGL.
 154
 155 ``EGL_RENDER_BUFFER``
 156 ~~~~~~~~~~~~~~~~~~~~~
 157
 158 In EGL, the color buffer a context should try to render to is decided by
 159 the binding surface. It should try to render to the front buffer if the
 160 binding surface has ``EGL_RENDER_BUFFER`` set to ``EGL_SINGLE_BUFFER``;
 161 If the same context is later bound to a surface with
 162 ``EGL_RENDER_BUFFER`` set to ``EGL_BACK_BUFFER``, the context should try
 163 to render to the back buffer. However, the context is allowed to make
 164 the final decision as to which color buffer it wants to or is able to
 165 render to.
 166
 167 For pbuffer surfaces, the render buffer is always ``EGL_BACK_BUFFER``.
 168 And for pixmap surfaces, the render buffer is always
 169 ``EGL_SINGLE_BUFFER``. Unlike window surfaces, EGL spec requires their
 170 ``EGL_RENDER_BUFFER`` values to be honored. As a result, a driver should
 171 never set ``EGL_PIXMAP_BIT`` or ``EGL_PBUFFER_BIT`` bits of a config if
 172 the contexts created with the config won't be able to honor the
 173 ``EGL_RENDER_BUFFER`` of pixmap or pbuffer surfaces.
 174
 175 It should also be noted that pixmap and pbuffer surfaces are assumed to
 176 be single-buffered, in that ``eglSwapBuffers`` has no effect on them. It
 177 is desirable that a driver allocates a private color buffer for each
 178 pbuffer surface created. If the window system the driver supports has
 179 native pbuffers, or if the native pixmaps have more than one color
 180 buffers, the driver should carefully attach the native color buffers to
 181 the EGL surfaces, re-route them if required.
 182
 183 There is no defined behavior as to, for example, how ``glDrawBuffer``
 184 interacts with ``EGL_RENDER_BUFFER``. Right now, it is desired that the
 185 draw buffer in a client API be fixed for pixmap and pbuffer surfaces.
 186 Therefore, the driver is responsible to guarantee that the client API
 187 renders to the specified render buffer for pixmap and pbuffer surfaces.
 188
 189 ``EGLDisplay`` Mutex
 190 ~~~~~~~~~~~~~~~~~~~~
 191
 192 The ``EGLDisplay`` will be locked before calling any of the dispatch
 193 functions (well, except for GetProcAddress which does not take an
 194 ``EGLDisplay``). This guarantees that the same dispatch function will
 195 not be called with the sample display at the same time. If a driver has
 196 access to an ``EGLDisplay`` without going through the EGL APIs, the
 197 driver should as well lock the display before using it.