Add missing headers. Change base class pqQVTKWidget
error: invalid use of incomplete type ‘XXXX'
And renderVTK() method was not existing in current base class of pqQVTKWidgetBase "QVTKOpenGLWidget.h", changed to "QVTKOpenGLSimpleWidget.h" This was discovered trying to compile paraview v5.5.2 with options:
cmake -GNinja -DCMAKE_BUILD_TYPE:STRING=Release
-DPARAVIEW_ENABLE_PYTHON:BOOL=ON
-DPARAVIEW_INSTALL_DEVELOPMENT_FILES=ON ../ParaView
using gcc 8.1.1 20180531