ENH: ctkVTKAbstractView: Update setUseDepthPeeling to also enable depth peel for volumes

This commit updates the method so that it also enables depth peeling for
volumes along with the translucent geometry. Only supported on OpenGL2
with dual-depth peeling.

Suggested-by: Ken Martin <ken.martin@kitware.com>

Libs/Visualization/VTK/Widgets/ctkVTKAbstractView.cpp

@@ -483,6 +483,9 @@ void ctkVTKAbstractView::setUseDepthPeeling(bool useDepthPeeling)
     }
   this->renderWindow()->SetMultiSamples(useDepthPeeling ? 0 : nSamples);
   renderer->SetUseDepthPeeling(useDepthPeeling ? 1 : 0);
+#if CTK_USE_QVTKOPENGLWIDGET
+  renderer->SetUseDepthPeelingForVolumes(useDepthPeeling);
+#endif
 }
 
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