Cannot show Volume on Plotter in qtwindow

I am following the code given in the examples but i could not get the volume view in qtwindow. I get a blank screen when i try to show Volume derived from ndarray but works fine on predefined shapes.

import sys
from PyQt5 import Qt
import numpy as np
from vtk.qt.QVTKRenderWindowInteractor import QVTKRenderWindowInteractor
from vtkplotter import Plotter, Volume, Cube, Sphere

class MainWindow(Qt.QMainWindow):
    def __init__(self, parent=None):

        Qt.QMainWindow.__init__(self, parent)
        self.frame = Qt.QFrame()
        self.vl = Qt.QVBoxLayout()
        self.vtkWidget = QVTKRenderWindowInteractor(self.frame)
        self.vl.addWidget(self.vtkWidget)

        vp = Plotter(qtWidget=self.vtkWidget, bg='black')

        c = Cube(side=30)
        s = Sphere(r=15)
        X, Y, Z = np.mgrid[:30, :30, :30]
        scalar_field = ((X-15)**2 + (Y-15)**2 + (Z-15)**2)/225
        vol = Volume(scalar_field)
        vol.alpha([0, 0, 0.4, 0.9, 0.9])

        # vp.show(c)
        # vp.show(s)
        vp.show(vol)

        self.frame.setLayout(self.vl)
        self.setCentralWidget(self.frame)

        self.show()    # <--- show the Qt Window

    def onClose(self):
        print("Disable the interactor before closing to prevent it from trying to act on a already deleted items")
        self.vtkWidget.close()


if __name__ == "__main__":
    app = Qt.QApplication(sys.argv)
    window = MainWindow()
    app.aboutToQuit.connect(window.onClose) # <-- connect the onClose event
    app.exec_()

The same Volume can be rendered without Plotter

import numpy as np
from vtkplotter import Volume

def main():
    X, Y, Z = np.mgrid[:30, :30, :30]
    scalar_field = ((X-15)**2 + (Y-15)**2 + (Z-15)**2)/225
    vol = Volume(scalar_field)
    vol.alpha([0, 0, 0.4, 0.9, 0.9])
    vol.show(bg="black")

if __name__ == '__main__':
    main()

[marcomusy]

Thanks @pasha009 ! I will add a comment in the example.

[pasha009]

This workaround is functioning for me. But no idea why. Just added

import vtk.qt
vtk.qt.QVTKRWIBase = "QGLWidget"

before any vtk imports