From Jan Ciger, "I have found a problem when building OSG with Qt 5 support. Qt has the
following in the qopengl.h header:

# include <QtGui/qopengles2ext.h>
# ifndef GL_DOUBLE
#  define GL_DOUBLE GL_FLOAT
# endif
# ifndef GLdouble
typedef GLfloat GLdouble;
# endif

Unfortunately, when building for normal OpenGL (not GL/ES!) on Windows
with MSVC2012, GLdouble is not defined (it is not a macro but typedef)
and the code above produces a conflicting definition, making the
compile fail. I am attaching a bit hackish workaround for this problem
in osg/GL "