Add a flag to make qt4 requirement optional

[Rauldg]

Allows the user to build Envire without qt4

[arneboe]

I think the rock_find_qt can be removed completely. No need for an extra flag. envire_core should not depend on qt

[arneboe]

I have removed the rock_find_qt4() call completely. It builds just fine. I think at some point during development the core used qt and this is a relict of that time. Thanks for pointing it out!

[Rauldg]

Here is some Qt dependent stuff.

Seems like those do not get build by default because without Qt installed the whole project still compiles.

[arneboe]

Ahh damn I forgot about the visualizations... We could move the visualizations to envire_visualizer? I think that was already discussed in #32. What do you think?

[Rauldg]

I like the idea too.

Would it break backward-compatibility?

[arneboe]

Hmm, it would break backward-compatibility for components that include the visualizers directly instead of loading them through vizkit3d. I think that the envire_visualizer is the only one doing that at the moment and we can fix that :) I'll give it a try

[saarnold]

The viz subfolder should be optional already. It is only build if the vizkit3d library is available. Additionally it can be excluded by setting ROCK_VIZ_ENABLED to OFF.

[arneboe]

Hmm ok, in that case I'll just leave it where it is :)

[Rauldg]

@saarnold

Even with the ROCK_VIZ_ENABLED set to OFF, cmake still depends on Qt to build successfully:

I added this line

message("ROCK VIZ ENABLED " ${ROCK_VIZ_ENABLED})

before the rock_find_qt4() line to make sure the variable was set and got this output:

-- Plugin system enabled
ROCK VIZ ENABLED OFF
qmake: could not exec '/usr/lib/x86_64-linux-gnu/qt4/bin/qmake': No such file or directory
CMake Error at /usr/share/cmake-3.5/Modules/FindQt4.cmake:1326 (message):
  Found unsuitable Qt version "" from NOTFOUND, this code requires Qt 4.x
Call Stack (most recent call first):
  /home/appuser/infuse/cdff/CDFF/External/install/share/rock/cmake/Rock.cmake:318 (find_package)
  CMakeLists.txt:41 (rock_find_qt4)

[arneboe]

rock_find_qt4() does not check for vizkit existence and also does not honor the ROCK_VIZ_ENABLED flag. It simply checks if qt exists. I think rock_find_qt4() should be removed from the main CMakeLists.txt (I have already removed it).

If needed we could add it to viz/CMakeLists.txt.

Alternatively we could use rock_find_qt4(OPTIONAL)

[saarnold]

There shouldn't be a rock_find_qt4() in the root CMakeLists.txt. Arne fixed this in this commit: https://github.com/envire/envire-envire_core/commit/759a8a50816176c4b31f09ba0f8f6f2f31d394ae Please check if you are on the current master branch.

Qt4 will be linked by the rock macros when the visualizations are included.