GL/gl.h, Qt5 and arm: FTBFS

[Steve Langasek]

Hi Lisandro,

On Mon, Mar 24, 2014 at 03:10:25PM -0300, Lisandro Damián Nicanor Pérez Meyer wrote:
> Hi! I'm trying to find a solution for the FTBFS of qantenna on arm* [0][1] 
> that fits the best to everyone. This issue seems to be very similar to a older 
> thread "including both GL/gl.h and cogl/cogl.h fails on armel and armhf" [2], 
> but I failed to see how that was resolved.

> The FTBFSs are due to conflicting declarations for GLdouble, GLsizeiptr and 
> GLintptr.

> Basically the problem might boild down to the fact that Qt5 is built using es2 
> instead of the "desktop" opengl which, to the best of my knowledge, it's 
> standard OpenGL 2.0.

> These are the possible solutions I think could be taken:

> a) Switch Qt5 to use "desktop" OpenGL on arm*. I have tested this on 
> harris.d.o and works OK. As a pro, it means that other apps will not have 
> porting issues like this. As a con, it might mean that all the OpenGL stuff 
> will be done by software though, am I correct?

Correct.  It is rare to find accelerated OpenGL drivers for ARM; almost all
the drivers out there, particularly for recent hardware, will be GLES2
instead.  This means that any reasonably GL-intensive app is going to be
unusable, particularly on armel.

FWIW, in Ubuntu not only is Qt built for GLES2 on armhf, we are also looking
at making a GLES2 build of Qt available on x86 - because for the mobile
sector, regardless of architecture, GLES2 is the relevant standard that
third-party drivers will be built to.

I don't think it makes sense to build Qt for OpenGL on arm.

> b) (supossing it's possible) provide es2 versions of mesa-common-dev, libglu1-
> mesa-dev et al. and build against that on arm*

Not really possible.  GLU depends on GL, not GLES2.  In theory it could be
ported, but this has not been done AFAIK.

> d) (also supossing it's possible) do not consider the FTBFS not RC (or allow 
> it's transition even if it's RC) until a better fix could be done.

The way to address this is to ask for the old arm binaries to be removed
from the archive, via a bug report against ftp.debian.org, with the
explanation that qantenna is not supported on GLES2 architectures.  This is
a perfectly reasonable thing to do under the circumstances.  Particularly
given that qantenna has always required GLU, and is unsupportable now
because GLU is not usable with Qt5 on arm*, I think this is the right thing
to do.

-- 
Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek at ubuntu.com                                     vorlon at debian.org
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