egl: automatically compile the `drm` platform when available
[mesa.git] / docs / egl.rst
2 ===
4 The current version of EGL in Mesa implements EGL 1.4. More information
5 about EGL can be found at
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.
13 The driver in use decides the window system to support.
15 Build EGL
16 ---------
18 #. Configure your build with the desired client APIs and enable the
19 driver for your hardware. For example:
21 .. code-block:: console
23 $ meson configure \
24 -D egl=true \
25 -D gles1=true \
26 -D gles2=true \
27 -D dri-drivers=... \
28 -D gallium-drivers=...
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.
35 #. Build and install Mesa as usual.
37 In the given example, it will build and install ``libEGL``, ``libGL``,
38 ``libGLESv1_CM``, ``libGLESv2``, and one or more EGL drivers.
40 Configure Options
41 ~~~~~~~~~~~~~~~~~
43 There are several options that control the build of EGL at configuration
44 time
46 ``-D egl=true``
47 By default, EGL is enabled. When disabled, the main library and the
48 drivers will not be built.
50 ``-D platforms=...``
51 List the platforms (window systems) to support. Its argument is a
52 comma separated string such as ``-D platforms=x11,wayland``. 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.
56 The available platforms are ``x11``, ``wayland``,
57 ``android``, and ``haiku``. The ``android`` platform
58 can either be built as a system component, part of AOSP, using
59 ```` files, or cross-compiled using appropriate options.
60 Unless for special needs, the build system should select the right
61 platforms automatically.
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.
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.
72 Use EGL
73 -------
75 Demos
76 ~~~~~
78 There are demos for the client APIs supported by EGL. They can be found
79 in mesa/demos repository.
81 Environment Variables
82 ~~~~~~~~~~~~~~~~~~~~~
84 There are several environment variables that control the behavior of EGL
85 at runtime
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.
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.
100 This changes the log level of the main library and the drivers. The
101 valid values are: ``debug``, ``info``, ``warning``, and ``fatal``.
103 EGL Drivers
104 -----------
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.
111 This driver can share DRI drivers with ``libGL``.
113 Packaging
114 ---------
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.
119 Developers
120 ----------
122 The sources of the main library and drivers can be found at
123 ``src/egl/``.
125 Lifetime of Display Resources
126 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
128 Contexts and surfaces are examples of display resources. They might live
129 longer than the display that creates them.
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``.
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.
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.
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.
156 ~~~~~~~~~~~~~~~~~~~~~
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.
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.
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.
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.
189 ``EGLDisplay`` Mutex
190 ~~~~~~~~~~~~~~~~~~~~
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.