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 @@ -19,216 +27,305 @@ 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.
+The driver in use decides the window system to support.
Build EGL
-
-
Run
+configure
with the desired state trackers and and enable -the Gallium driver for your hardware. For exampleRun
configure
with the desired client APIs and enable +the driver for your hardware. For example- $ ./configure --with-state-trackers=egl,es,vega --enable-gallium-intel + $ ./configure --enable-gles1 --enable-gles2 \ + --with-dri-drivers=... \ + --with-gallium-drivers=...
-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.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 libEGL
,
-libGLESv1_CM
, libGLESv2
, libOpenVG
, and
-one or more EGL drivers.
libGL
, libGLESv1_CM
, libGLESv2
, and one
+or more EGL drivers.
Configure Options
There are several options that control the build of EGL at configuration time
--
-
--enable-egl
+-
+
--enable-egl
+-
By default, EGL is enabled. When disabled, the main library and the drivers will not be built.
-
+
---with-egl-displays
+ +--with-egl-driver-dir
- -
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).The directory EGL drivers should be installed to. If not specified, EGL +drivers will be installed to
-${libdir}/egl
.
+
---with-state-trackers
+ +--enable-gallium-egl
- -
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 theegl
state tracker.Enable the optional
-egl_gallium
driver.
+
---enable-gallium-swrast
+ +--with-egl-platforms
- -
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.
+List the platforms (window systems) to support. Its argument is a comma +separated 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 asEGLNativeDisplayType
or +EGLNativeWindowType
defined for.
-
The available platforms are x11
, drm
,
+fbdev
, and gdi
. The gdi
platform can
+only be built with SCons. Unless for special needs, the build system should
+select the right platforms automatically.
--enable-gles1
--enable-gles2
OpenGL
+These options enable OpenGL ES support in OpenGL. The result is one big +internal library that supports multiple APIs.
-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/
.
--enable-shared-glapi
By default, libGL
has its own copy of libglapi
.
+This options makes libGL
use the shared libglapi
. This
+is required if applications mix OpenGL and OpenGL ES.
--enable-openvg
OpenVG must be explicitly enabled by this option.
+ +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,
Demos
-- $ cd progs/es1/xegl - $ make - $ ./torus -+
There are demos for the client APIs supported by EGL. They can be found in +mesa/demos repository.
Environment Variables
There are several environment variables that control the behavior of EGL at runtime
--
-
EGL_DRIVER
+-
+
EGL_DRIVERS_PATH
+-
-
This variable forces the specified EGL driver to be loaded. It comes in -handy when one wants to test a specific driver.
+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.
-
+EGL_DISPLAY
++ $ export LD_LIBRARY_PATH=$mesa/lib + $ export EGL_DRIVERS_PATH=$mesa/lib/egl +
-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
orkms
. 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. +to test a build without installation
-
+
+
+EGL_DRIVER
+-
+
+
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.
+ +
+
+ EGL_PLATFORM
+-
+
+
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-platforms
as the native platform.Extensions like
+ +EGL_MESA_drm_display
define 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.
- EGL_LOG_LEVEL
+ +EGL_LOG_LEVEL
This changes the log level of the main library and the drivers. The valid values are:
-debug
,info
,warning
, andfatal
.
+
-EGL_SOFTWARE
+ +EGL_SOFTWARE
For drivers that support both hardware and software rendering, setting this variable to true forces the use of software rendering.
-
-
This variable is usually set to test an uninstalled build. For example, one +may set
-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_dri2
+-
-
-egl_xdri
+This driver supports both
-x11
anddrm
platforms. +It functions as a DRI driver loader. Forx11
support, it talks to +the X server directly using (XCB-)DRI2 protocol.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 onlibGL
. 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 withegl_glx
.This driver can share DRI drivers with
-libGL
.egl_dri
+
- egl_gallium
+- - -
-
+
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.
This driver is based on Gallium3D. It supports all rendering APIs and +hardware supported by Gallium3D. It is the only driver that supports OpenVG. +The supported platforms are X11, DRM, FBDEV, and GDI.
-To use the classic drivers, one must manually set EGL_DRIVER
at
-runtime.
This driver comes with its own hardware drivers
+(pipe_<hw>
) and client API modules
+(st_<api>
).
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/
.
+Packaging
-TODOs
+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
+distribution.
-
-
- Thread safety -
- Pass the conformance tests -
- Better automatic driver selection:
EGL_DISPLAY
loads all -drivers and might eat too much memory.
+
Generally, egl_dri2
is preferred over egl_gallium
+when the system already has DRI drivers. As egl_gallium
is loaded
+before egl_dri2
when both are available, egl_gallium
+is disabled by default.
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/
.
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 eglTerminate
, all
+display resources should be destroyed. Similarly, when a thread is released
+through eglReleaseThread
, all current display resources should be
+released. Another way to destroy or release resources is through functions
+such as eglDestroySurface
or eglMakeCurrent
.
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
+driver's MakeCurrent
callback,
+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
+uninitialized display.
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.
+ +EGL_RENDER_BUFFER
+
+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
+surface has EGL_RENDER_BUFFER
set to
+EGL_SINGLE_BUFFER
; If the same context is later bound to a
+surface with 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
+always EGL_SINGLE_BUFFER
. Unlike window surfaces, EGL spec
+requires their EGL_RENDER_BUFFER
values to be honored. As a
+result, a driver should never set EGL_PIXMAP_BIT
or
+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
+pbuffer surfaces.
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
+required.
There is no defined behavior as to, for example, how
+glDrawBuffer
interacts with EGL_RENDER_BUFFER
. Right
+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
+surfaces.
EGLDisplay
Mutex
+
+The EGLDisplay
will 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 EGLDisplay
without going through the EGL APIs, the driver
+should as well lock the display before using it.
+
+