The current version of EGL in Mesa implements EGL 1.4. More information about EGL can be found at http://www.khronos.org/egl/.
The Mesa's implementation of EGL uses a driver architecture. The main
libEGL) is window system neutral. It provides the EGL
API entry points and helper functions for use by the drivers. Drivers are
dynamically loaded by the main library and most of the EGL API calls are
directly dispatched to the drivers.
The driver in use decides the window system to support.
configurewith the desired client APIs and enable the driver for your hardware. For example
$ ./configure --enable-gles1 --enable-gles2 \ --with-dri-drivers=... \ --with-gallium-drivers=...
The main library and OpenGL is enabled by default. The first two options above enables OpenGL ES 1.x and 2.x. The last two options enables the listed classic and and Gallium drivers respectively.
- Build and install Mesa as usual.
In the given example, it will build and install
libGLESv2, and one
or more EGL drivers.
There are several options that control the build of EGL at configuration time
By default, EGL is enabled. When disabled, the main library and the drivers will not be built.
The directory EGL drivers should be installed to. If not specified, EGL drivers will be installed to
Enable the optional
List the platforms (window systems) to support. Its argument is a comma seprated string such as
--with-egl-platforms=x11,drm. It decides the platforms a driver may support. The first listed platform is also used by the main library to decide the native platform: the platform the EGL native types such as
The available platforms are
gdiplatform can only be built with SCons. Unless for special needs, the build system should select the right platforms automatically.
These options enable OpenGL ES support in OpenGL. The result is one big internal library that supports multiple APIs.
libGLhas its own copy of
libglapi. This options makes
libGLuse the shared
libglapi. This is required if applications mix OpenGL and OpenGL ES.
OpenVG must be explicitly enabled by this option.
There are demos for the client APIs supported by EGL. They can be found in mesa/demos repository.
There are several environment variables that control the behavior of EGL at runtime
By default, the main library will look for drivers in the directory where the drivers are installed to. This variable specifies a list of colon-separated directories where the main library will look for drivers, in addition to the default directory. This variable is ignored for setuid/setgid binaries.
This variable is usually set to test an uninstalled build. For example, one may set
$ export LD_LIBRARY_PATH=$mesa/lib $ export EGL_DRIVERS_PATH=$mesa/lib/egl
to test a build without installation
This variable specifies a full path to or the name of an EGL driver. It forces the specified EGL driver to be loaded. It comes in handy when one wants to test a specific driver. This variable is ignored for setuid/setgid binaries.
This variable specifies the native platform. The valid values are the same as those for
--with-egl-platforms. When the variable is not set, the main library uses the first platform listed in
--with-egl-platformsas the native platform.
EGL_MESA_drm_displaydefine new functions to create displays for non-native platforms. These extensions are usually used by applications that support non-native platforms. Setting this variable is probably required only for some of the demos found in mesa/demo repository.
This changes the log level of the main library and the drivers. The valid values are:
For drivers that support both hardware and software rendering, setting this variable to true forces the use of software rendering.
This driver supports both
drmplatforms. It functions as a DRI driver loader. For
x11support, it talks to the X server directly using (XCB-)DRI2 protocol.
This driver can share DRI drivers with
This driver is based on Gallium3D. It supports all rendering APIs and hardwares supported by Gallium3D. It is the only driver that supports OpenVG. The supported platforms are X11, DRM, FBDEV, and GDI.
This driver comes with its own hardware drivers (
pipe_<hw>) and client API modules (
This driver provides a wrapper to GLX. It uses exclusively GLX to implement the EGL API. It supports both direct and indirect rendering when the GLX does. It is accelerated when the GLX is. As such, it cannot provide functions that is not available in GLX or GLX extensions.
The ABI between the main library and its drivers are not stable. Nor is
there a plan to stabilize it at the moment. Of the EGL drivers,
egl_gallium has its own hardware drivers and client API modules.
They are considered internal to
egl_gallium and there is also no
stable ABI between them. These should be kept in mind when packaging for
egl_dri2 is preferred over
when the system already has DRI drivers. As
egl_gallium is loaded
egl_dri2 when both are available,
is disabled by default.
The sources of the main library and the classic drivers can be found at
src/egl/. The sources of the
egl state tracker can
be found at
The suggested way to learn to write a EGL driver is to see how other drivers
egl_glx should be a good reference. It works in any
environment that has GLX support, and it is simpler than most drivers.
Lifetime of Display Resources
Contexts and surfaces are examples of display resources. They might live longer than the display that creates them.
In EGL, when a display is terminated through
display resources should be destroyed. Similarly, when a thread is released
eglReleaseThread, all current display resources should be
released. Another way to destory or release resources is through functions
When a resource that is current to some thread is destroyed, the resource
should not be destroyed immediately. EGL requires the resource to live until
it is no longer current. A driver usually calls
eglIs<Resource>Bound to check if a resource is bound
(current) to any thread in the destroy callbacks. If it is still bound, the
resource is not destroyed.
The main library will mark destroyed current resources as unlinked. In a
eglIs<Resource>Linked can then be called to check if a newly
released resource is linked to a display. If it is not, the last reference to
the resource is removed and the driver should destroy the resource. But it
should be careful here because
MakeCurrent might be called with an
This is the only mechanism provided by the main library to help manage the resources. The drivers are responsible to the correct behavior as defined by EGL.
In EGL, the color buffer a context should try to render to is decided by the
binding surface. It should try to render to the front buffer if the binding
EGL_RENDER_BUFFER set to
EGL_SINGLE_BUFFER; If the same context is later bound to a
EGL_RENDER_BUFFER set to
EGL_BACK_BUFFER, the context should try to render to the back
buffer. However, the context is allowed to make the final decision as to which
color buffer it wants to or is able to render to.
For pbuffer surfaces, the render buffer is always
EGL_BACK_BUFFER. And for pixmap surfaces, the render buffer is
EGL_SINGLE_BUFFER. Unlike window surfaces, EGL spec
EGL_RENDER_BUFFER values to be honored. As a
result, a driver should never set
EGL_PBUFFER_BIT bits of a config if the contexts created with the
config won't be able to honor the
EGL_RENDER_BUFFER of pixmap or
It should also be noted that pixmap and pbuffer surfaces are assumed to be
single-buffered, in that
eglSwapBuffers has no effect on them. It
is desirable that a driver allocates a private color buffer for each pbuffer
surface created. If the window system the driver supports has native pbuffers,
or if the native pixmaps have more than one color buffers, the driver should
carefully attach the native color buffers to the EGL surfaces, re-route them if
There is no defined behavior as to, for example, how
glDrawBuffer interacts with
now, it is desired that the draw buffer in a client API be fixed for pixmap and
pbuffer surfaces. Therefore, the driver is responsible to guarantee that the
client API renders to the specified render buffer for pixmap and pbuffer
EGLDisplaywill be locked before calling any of the dispatch functions (well, except for GetProcAddress which does not take an
EGLDisplay). This guarantees that the same dispatch function will not be called with the sample display at the same time. If a driver has access to an
EGLDisplaywithout going through the EGL APIs, the driver should as well lock the display before using it.