void viewport_OutputChanged(object sender, RectChangedEventArgs e)
 {
     OnOutputChanged(e.newRect, e.oldRect);
 }
 void viewport_OutputChanged(object sender, RectChangedEventArgs e)
 {
     OnOutputChanged(e.newRect, e.oldRect);
 }
 void viewport_VisibleChanged(object sender, RectChangedEventArgs e)
 {
     OnVisibleChanged(e.newRect, e.oldRect);
 }
 void viewport_VisibleChanged(object sender, RectChangedEventArgs e)
 {
     OnVisibleChanged(e.newRect, e.oldRect);
 }