TocWidget: Fix perf regression

4d1ad336 fixed #9754 but caused perf issues by cancelling the gains of having a
timer (introduced after #7138). This introduces in GuiToc::enableView() a
lightweight check of whether the widget should be updated. The logic is inspired
from GuiViewSource::enableView().

src/frontends/qt4/GuiToc.cpp

@@ -66,9 +66,12 @@ void GuiToc::dispatchParams()
 }
 
 
-void GuiToc::enableView(bool /*enable*/)
+void GuiToc::enableView(bool enable)
 {
-	widget_->updateViewForce();
+	widget_->checkModelChanged();
+	if (!enable)
+		// In the opposite case, updateView() will be called anyway.
+		widget_->updateViewForce();
 }
 
 

src/frontends/qt4/TocWidget.cpp

@@ -452,6 +452,14 @@ void TocWidget::updateViewForce()
 }
 
 
+void TocWidget::checkModelChanged()
+{
+	if (!gui_view_.documentBufferView() ||
+	    gui_view_.tocModels().model(current_type_) != tocTV->model())
+		updateViewForce();
+}
+
+
 void TocWidget::filterContents()
 {
 	if (!tocTV->model())

src/frontends/qt4/TocWidget.h

@@ -42,6 +42,8 @@ public:
 	///
 	bool getStatus(Cursor & cur, FuncRequest const & fr, FuncStatus & status)
 		const;
+	// update the view when the model has changed
+	void checkModelChanged();
 
 public Q_SLOTS:
 	/// Schedule new update of the display unless already scheduled.