[05/14,v6] package/mesa3d-headers: new package

Some headers required to build GL/EGL/GLES/... stuff are not provided by
Khronos, so we must find an alternate source for those headers.
Currently, we're missing:
  - gl.h for full GL (gl.h for GLES is available from Khronos)
  - dri_interface.h to be able to build GL-enabled Xorg

mesa3d provides all of them, and they are generic enough that they can
be re-used even for other GL/EGL/GLES/... implementations.

Unfortunately, modifying mesa3d so that it only installs its headers is
no trivial task, and would render the mesa3d package really ugly and
unmaintainable in the long run.

Instead, we introduce a stripped-down mesa3d-headers package, which sole
purpose is to install those missing headers.

Alongside the dri_interface.h header, we also need to install a
pkg-config file, dri.pc, so that Xorg et al. are content and believe
they have DRI available.

Since we do only really require a very limited subset of files from
mesa3d, we do not really care of the version we use, so there is no
reason to keep them both in sync, and no reason to add a comment in
mesa3d to that effect.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

---
Notes:

It should not be possible to select both mesa3d *and* mesa3d-headers at
the same time, but it is difficult to foresee the multiple combinations
we may have, due to poor understanding on how binary drivers may behave
and may require, as well as my own poor understanding of the GL stack(s).

So I decided to just print a warning in that case, and just depend on
mesa3d, which would ultimately provide the headers we are interested in
anyway. This can be turned into an error if preferred.
---
 package/Config.in                          |  1 +
 package/mesa3d-headers/Config.in           |  8 +++++
 package/mesa3d-headers/mesa3d-headers.hash |  2 ++
 package/mesa3d-headers/mesa3d-headers.mk   | 57 ++++++++++++++++++++++++++++++
 4 files changed, 68 insertions(+)
 create mode 100644 package/mesa3d-headers/Config.in
 create mode 100644 package/mesa3d-headers/mesa3d-headers.hash
 create mode 100644 package/mesa3d-headers/mesa3d-headers.mk

Hello Yann,

On Saturday 24 January 2015 00:24:34 Yann E. MORIN wrote:
> Some headers required to build GL/EGL/GLES/... stuff are not provided by
> Khronos, so we must find an alternate source for those headers.
> Currently, we're missing:
>   - gl.h for full GL (gl.h for GLES is available from Khronos)
>   - dri_interface.h to be able to build GL-enabled Xorg
> 
> mesa3d provides all of them, and they are generic enough that they can
> be re-used even for other GL/EGL/GLES/... implementations.
> 
> Unfortunately, modifying mesa3d so that it only installs its headers is
> no trivial task, and would render the mesa3d package really ugly and
> unmaintainable in the long run.
Did you try "make install-data" in mesa3d tree? It should install all 
files but the libraries (in other terms, it install headers only).


> Instead, we introduce a stripped-down mesa3d-headers package, which sole
> purpose is to install those missing headers.
hmmm... since mesa3d-headers provide all headers, do we really need 
khronos-registry-* packages? In add, all developers test their code 
using mesa3d headers. So, I would prefer to use headers provided by 
mesa3d than khronos.

[...]

Jérôme, All,

On 2015-01-26 09:54 +0100, Jérôme Pouiller spake thusly:
> On Saturday 24 January 2015 00:24:34 Yann E. MORIN wrote:
> > Some headers required to build GL/EGL/GLES/... stuff are not provided by
> > Khronos, so we must find an alternate source for those headers.
> > Currently, we're missing:
> >   - gl.h for full GL (gl.h for GLES is available from Khronos)
> >   - dri_interface.h to be able to build GL-enabled Xorg
> > 
> > mesa3d provides all of them, and they are generic enough that they can
> > be re-used even for other GL/EGL/GLES/... implementations.
> > 
> > Unfortunately, modifying mesa3d so that it only installs its headers is
> > no trivial task, and would render the mesa3d package really ugly and
> > unmaintainable in the long run.
> Did you try "make install-data" in mesa3d tree? It should install all 
> files but the libraries (in other terms, it install headers only).

I thought of doing just that, indeed.

But then, it is only possible to run 'make install-anything' if the
package had previously been configured and built, i.e. './configure' and
.make' were previously called.

But then, what flags are we supposed to pass ./configure ? We surely do
not want to enable everything, jsut what is needed to get the headers.

And then, we would have to carefuly call 'make' so that it does not
build everything, just the headers.

> > Instead, we introduce a stripped-down mesa3d-headers package, which sole
> > purpose is to install those missing headers.
> hmmm... since mesa3d-headers provide all headers, do we really need 
> khronos-registry-* packages? In add, all developers test their code 
> using mesa3d headers. So, I would prefer to use headers provided by 
> mesa3d than khronos.

Well, I'm not really against droippign the Khronos registries, since it
is not fun packaging those.

However, as I said above, we'd have to carefuly craft mesa3d-headers to
just configure and build the headers, and I'm afraid that's not so
easy...

But I can give it a shot to see how dirty/difficult it would be.

Regards,
Yann E. MORIN.