[Mesa-dev] Drooping multiple driver support in EGL?

[Chia-I Wu]

Hi list,

Multiple driver support in EGL is hard to get right, if not impossible.
On Linux desktop, we almost always want to use egl_dri2.  It allows EGL
to loads DRI2 drivers, thus allowing it to share DRI2 drivers with
libGL.

In one case where the app wants to use OpenVG, libEGL needs to load
egl_gallium instead.  The problem comes from that we cannot know that an
OpenVG context is to be created until it is created.  But before a
context can be created, EGL needs to be initialized and an EGLConfig
needs to be chosen.  So when EGL is to be initialized, we need to load
and initilaize all EGL drivers.  When an EGLConfig is to be picked, we
need to pick it from all drivers.

But this also introduces new problems.   For example, when the vendor
string or the extension string is queried, whose string of all EGL
drivers should be returned?

My proposal is to simply drop multiple driver support from EGL.
Instead, we will provide four libEGL implementations:

 - libEGL_dri2: derived from egl_dri2
 - libEGL_gallium: derived from egl_gallium
 - libEGL_glx: derived from egl_glx
 - libEGL_loader: see below

All of them are conformant EGL implementations.  That is, any one of
them can be installed as /usr/lib/libEGL.so.

libEGL_loader is new.  It is basically a wrapper that loads another
implementation to do the real work.  As such, the problems we face with
multiple driver support will remain in libEGL_loader.

Distros may choose to install libEGL_loader as libEGL and let it pick
the real implementation.  Or they may choose to have the first three
installed as libEGL, and package them separately.

Thoughts?

-- 
olv at LunarG.com