Move #include out of namespace, use <cmath>
With gcc 6 I'm getting:
In file included from /usr/include/c++/6.0.0/math.h:36:0,
from /builddir/build/BUILD/ParaView-v5.0.0-source/Plugins/PointSprite/Qvis/VolumeAttributes.cpp:1828:
/usr/include/c++/6.0.0/cmath:101:37: error: '__is_integer' was not declared in this scope
typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,
^~~~~~~~~~~~
/usr/include/c++/6.0.0/cmath:101:37: note: suggested alternative:
In file included from /usr/include/c++/6.0.0/bits/stl_algobase.h:61:0,
from /usr/include/c++/6.0.0/bits/char_traits.h:39,
from /usr/include/c++/6.0.0/string:40,
from /builddir/build/BUILD/ParaView-v5.0.0-source/Plugins/PointSprite/Qvis/VolumeAttributes.h:40,
from /builddir/build/BUILD/ParaView-v5.0.0-source/Plugins/PointSprite/Qvis/VolumeAttributes.cpp:38:
/usr/include/c++/6.0.0/bits/cpp_type_traits.h:127:12: note: 'std::__is_integer'
struct __is_integer
^~~~~~~~~~~~
All #includes really should be at the top, and especially out of namespace {} blocks. Also, I believe is preferred over <math.h> in C++.