[OE-core] [oe] [RFC] OpenGL packaging/staging policy

[Phil Blundell]

On Mon, 2012-10-22 at 17:35 +0100, Burton, Ross wrote:
> Rule 3. Only Mesa stages, nothing else
> 
> Whilst there are multiple GL implementations that offer various
> subsets of GL, they are all effectively interchangeable.  It's not a
> massive concern what exact GL is present when building because they've
> all got the same API.

This is an attractive idea but I'm not sure that the underlying
assumption is entirely correct.

Different GL libraries will have different vendor extensions and Mesa's
headers won't necessarily know about them.  If the vendor ships the
extension bits in a custom header (rather than jamming them into a
modified glext.h) then this could be worked around by staging the
headers separately, but you're still left with the problem that Mesa's
libGL.so might now be missing symbols that are required during
linking.  

Also, even if the APIs were the same, I am slightly nervous about
relying on all vendor GLs having an identical ABI to Mesa.  I can't
immediately think of any reason why they shouldn't but, equally, vendors
have been known to do peculiar things in the past and I wouldn't be
totally shocked to find that there is some binary libGL out there which
manages to be ABI-incompatible with Mesa in some or other creative
fashion.

p.