Mesa EGL

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 library (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. For drivers that support hardware rendering, there are usually multiple drivers supporting the same window system. Each one of of them supports a certain range of graphics cards.

Build EGL

Run configure with the desired state trackers and and enable the Gallium driver for your hardware. For example
```
  $ ./configure --with-state-trackers=egl,es,vega --enable-gallium-{swrast,intel}
```
The main library will be enabled by default. The egl state tracker is needed by a number of EGL drivers. EGL drivers will be covered later. The es state tracker provides OpenGL ES 1.x and 2.x and the vega state tracker provides OpenVG 1.x.
Build and install Mesa as usual.

In the given example, it will build and install libEGL, libGLESv1_CM, libGLESv2, libOpenVG, and one or more EGL drivers.

Configure Options

There are several options that control the build of EGL at configuration time

--enable-egl
By default, EGL is enabled. When disabled, the main library and the drivers will not be built.
--with-egl-driver-dir
The directory EGL drivers should be installed to. If not specified, EGL drivers will be installed to ${libdir}/egl.
--with-egl-displays
List the window system(s) to support. It is by default x11, which supports the X Window System. Its argument is a comma separated string like, for example, --with-egl-displays=x11,kms. Because an EGL driver decides which window system to support, this example will enable two (sets of) EGL drivers. One supports the X window system and the other supports bare KMS (kernel modesetting).
--with-state-trackers
The argument is a comma separated string. It is usually used to specify the rendering APIs, like OpenGL ES or OpenVG, to build. But it should be noted that a number of EGL drivers depend on the egl state tracker. They will not be built without the egl state tracker.
--enable-gallium-swrast
This option is not specific to EGL. But if there is no driver for your hardware, or you are experiencing problems with the hardware driver, you can enable the swrast DRM driver. It is a dummy driver and EGL will fallback to software rendering automatically.

OpenGL

The OpenGL state tracker is not built in the above example. It should be noted that the classic libGL is not a state tracker and cannot be used with EGL (unless the EGL driver in use is egl_glx). To build the OpenGL state tracker, one may append glx to --with-state-trackers and manually build src/gallium/winsys/xlib/.

Use EGL

The demos for OpenGL ES and OpenVG can be found in progs/es1/, progs/es2/ and progs/openvg/. You can use them to test your build. For example,

  $ cd progs/es1/xegl
  $ make
  $ ./torus

Environment Variables

There are several environment variables that control the behavior of EGL at runtime

EGL_DRIVER
This variable forces the specified EGL driver to be loaded. It comes in handy when one wants to test a specific driver.
EGL_DISPLAY
When EGL_DRIVER is not set, the main library loads all EGL drivers that support a certain window system. EGL_DISPLAY can be used to specify the window system and the valid values are, for example, x11 or kms. When the variable is not set, the main library defaults the value to the first window system listed in --with-egl-displays at configuration time.
EGL_LOG_LEVEL
This changes the log level of the main library and the drivers. The valid values are: debug, info, warning, and fatal.
EGL_SOFTWARE
For drivers that support both hardware and software rendering, setting this variable to true forces the use of software rendering.

EGL Drivers

There are two categories of EGL drivers: Gallium and classic.

Gallium EGL drivers supports all rendering APIs specified in EGL 1.4. The support for optional EGL functions and EGL extensions is usually more complete than the classic ones. These drivers depend on the egl state tracker to build. The available drivers are

egl_<dpy>_i915
egl_<dpy>_i965
egl_<dpy>_radeon
egl_<dpy>_nouveau
egl_<dpy>_swrast
egl_<dpy>_vmwgfx

<dpy> is given by --with-egl-displays at configuration time. There will be one EGL driver for each combination of the displays listed and the hardware drivers enabled.

Classic EGL drivers, on the other hand, supports only OpenGL as its rendering API. They can be found under src/egl/drivers/. There are 3 of them

egl_glx
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.
egl_xdri
This driver supports the X Window System as its window system. It functions as a DRI driver loader and can load DRI/DRI2/DRISW drivers. Unlike egl_glx, it has no dependency on libGL. It talks to the X server directly using DRI or DRI2 protocols. It also talks minimal GLX protocol for things like available visuals or fbconfigs. With direct access to the DRI drivers, it has the potential to support more EGL functions that are not possible with egl_glx.
egl_dri
This driver lacks maintenance and does not build. It is similiar to egl_xdri in that it functions as a DRI driver loader. But unlike egl_xdri, it supports Linux framebuffer devices as its window system and supports EGL_MESA_screen_surface extension. It loads only DRI1 drivers. As DRI1 drivers is phasing out, it might be better to rewrite the driver to support KMS and DRI2.

To use the classic drivers, one must manually set EGL_DRIVER at runtime.

Developers

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 src/gallium/state_trackers/egl/.

TODOs

Thread safety
Pass the conformance tests
Better automatic driver selection: EGL_DISPLAY loads all drivers and might eat too much memory.
Stop using glxinit.c and sources from src/glx/x11/