Fixing parameters reloaded when testing camera. Also fixed app freezing when closing Preferences dialog after using test camera dialog

app/src/main.cpp

@@ -60,6 +60,12 @@ int main(int argc, char* argv[])
     QSurfaceFormat::setDefaultFormat(QVTKRenderWidget::defaultFormat());
 #endif
 
+	// Recommended by VTK when using QVTKOpenGLNativeWidget (a QOpenGLWidget): let all VTK
+	// render widgets share a single OpenGL context, which is needed for correct rendering
+	// when render widgets live in / move across multiple top-level windows. Must be set
+	// before QApplication is constructed.
+	QApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
+
 	/* Create tasks */
 	QApplication * app = new QApplication(argc, argv);
 	app->setStyleSheet("QMessageBox { messagebox-text-interaction-flags: 5; }"); // selectable message box