title: QVTKWidget is transparent
body: <p>I am just a beginner in both Qt and PCL. I am trying to display PCL viewer in the main Qt GUI Window. When I use PCL viewer, it shows up in the separate window. I also try with <strong>QVTKWidget</strong>.The problem is that when I run the program, the QVTKWidget become <strong>transparent</strong> and cannot load point cloud. I run in Ubuntu 18.04 , Qt 5.9.5, PCL 1.8, Vtk 6.3. Please give me some advice.</p>