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

1. 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-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.

2. 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-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

TODOs

• Thread safety
• Pass the conformance tests
• Better automatic driver selection: EGL_DISPLAY loads all drivers and might eat too much memory.