On 06/10/15 20:58, Kyle Brenneman wrote:
On 10/06/2015 12:43 PM, Emil Velikov wrote:
On 6 October 2015 at 16:39, Kyle Brenneman <kbrenne...@nvidia.com> wrote:
On 10/06/2015 07:34 AM, Emil Velikov wrote:
Hello Kyle,
A few questions/points of discussion:
* What is your take on having a libglvnd 'package', which provides
the headers (and maybe other materials), apart from the libraries ?
I'm basically thinking about OpenGL.h, GLX.h, etc for programs that
wish to use new ABI, and glvnd{Foo,Bar}.h which mesa and other GL
implementations.
I haven't looked much into packaging yet. I'm open to any suggestions that
might make that easier, though.
One thing that I'm planning to do but haven't gotten to yet is to move the
public headers into a separate directory. There's a couple of header files
(libglxabi.h and GLdispatchABI.h) that are intended to be used by vendor
library implementations, and the other headers are all internal.
The headers that you'd use for compiling an application (gl.h, glx.h, etc.)
could easily go into a separate package, too.
By 'packaging' I meant that the relevant files are available after
`make install'. Currently for GLdispatchABI.h and others that's not
the case. We can leave it up-to the distributions to manage the actual
packages (if in doubt a document to guide them), but we can make sure
that the files (including pkg-config and cmake ones, separate set for
user/developer) are there.
The 'make install' command currently doesn't do anything with the
regular GL headers. I would expect that if someone's building an OpenGL
application, then they've probably already installed some version of the
GL headers separately. Still, I could probably add a configure option or
something to include them.
Pretty much what I was wondering. Mostly as I've noticed that the
official Nvidia driver has started shipping some headers which clash
with mesa ones :'( Perhaps the AMD proprietary driver ships some as well ?
Including the public ABI headers in a "make install" does sound like a
good idea. Maybe put them next to the normal GL headers, or under a
GLVND subdirectory?
A separate location sounds better imho. Then again this information will
be made available via the .pc .cmake files. People that don't use them
can hardcode thing as needed :)
[snip]
* There was an idea to expose separate libOpenGL libraries, one for
each (major?) GL version.
What happened on that front ?
Nothing as far as I know.
However, each of those libraries is basically just a thin wrapper around
libGLdispatch.so, so in theory you could define any number of libraries that
just export a different set of functions. It's more a question of how many
libraries we'd want to deal with.
From an application standpoint, having a fixed set of libraries with a known
set of exported functions seems like the easiest option, since you could
then link your application against it and not have to modify it later.
That said, the set of functions to export from libGL.so and libOpenGL.so is
still an open question. The set right now is just what libglvnd inherited
from Mesa, but it would be good to have a more clearly-defined set. Maybe
something simple like all core OpenGL functions through version 4.5 or so?
I'm rather inclined towards "(ideally) no GL symbols should be
statically available" - just use *gl*GetProcAddress. Otherwise thing
are bound to get quite hairy.
- Forward/backward compatibility
- Incorrectly linked - program uses GL N, yet linked against GL N+1.
- Developer confusion - which library do I need, how do I check for X
and not Y.
- The easy way out - using GL N core function glFoo, link against GL
N, rather than LG N-1 + doing the extension check.
Note that libGL.so from older mesa was exposing a few too many symbols
statically, so we might want to make sure these/similar changes landed
in libglvnd.
libGLX.so itself only exports GLX 1.4 functions -- no extensions and no
OpenGL functions. If an app developer wants to, they could link against
only libGLX.so, and then use glXGetProcAddress to look up every OpenGL
function.
libOpenGL.so is there to avoid the hassle of having looking up every
OpenGL function, especially in simpler apps that don't need to use many
extension functions.
Developer confusion is why I think it would be best to define a set of
functions to export and just stick with it.
Greater confusion will come with the various different lists, imho. Esp.
since there will be some overlap but they (the lists) won't be quite the
same between the old and new ABI.
It would be easier to have a macro/helper that fetches any entry point
required via gl*GetProcAddress, rather having divergent flow based on
heuristics X.
See for example how GLEW does not always get it right, thus libepoxy was
born. I suspect a similar thing will happen for the new ABI.
As long as the set of
exported functions stays consistent between versions, then a developer
can rely on it without getting missing or duplicate symbol errors every
time a new libglvnd version comes along.
This will work mainly for the experienced developers. For newcommers
(people doing small apps), this is bound to cause serious headache.
If the general consensus is in favour of the static exports, then I
would strongly suggest:
- No libOpenGL for GL X and another for Y. Just have a single library.
Otherwise you'll get into the issues mentioned earlier.
- libglvnd tests need to ensure no extra symbols get exported.
For backward compatibility with existing applications, libGL.so and
libGLES*.so would still need to be there, but those might have a
different set of exports than libOpenGL.so.
This will lead to even further confusion, imho. Think of the case - am I
using the old or the new ABI, did which symbols did that one exported
again... Ahh yes, not the ones available in the old ABI :\
By the spec, libGL.so only
exports OpenGL 1.2 functions, but most libGL.so implementations out
there export a lot more, and some buggy apps depend on that.
If you don't export any, there is no way for people to unintentionally
{ab,}use it. Starting off clean would be great imho.
I won't babble any more on the topic. Hopefully my ideas/concerns came
across without being too pedantic.
* The existing x11glvnd extension seems to be a "xserver only" approach.
Iirc at XDC last year, people were leaning towards using an FD to
obtain all the information needed. Currently mesa/xserver uses that to
detect if we should load i915, i965, r300, r600... driver. What's your
take on this ?
I'm open to alternatives, but I'm not familiar with the FD approach you're
describing. Can you give me more details about it, or point me at where in
the Mesa code it is?
The idea is that you can get the device(node) fd from the server
(x,weston,foo) and use that to communicate with the module and/apply
any form of heuristics. Currently mesa has a few:
- get the kernel module name (via ioctls or sysfs) and map it to the
userspace driver.
- get the vendor/device pciid (via libudev or sysfs), and map it to
the userspace driver.
The code is in src/loader, it's a bit hard to look at, so be warned.
I've been planning to nuke the ioctl vs sysfs vs libudev, by pushing
the chaos to libdrm. So that others can reuse it when needed. yet it's
not the most interesting thing to do bth.
The only thing that libGLX can assume is that each X screen corresponds
to at most one vendor library. A vendor library might be libdrm-based or
might not. It might be a purely software-based implementation that
doesn't even use the GLX extension,
I'm confused - isn't x11glvnd suppose to communicate with libGLX ? How
can that happen if there is no GLX extension ?
