Added crosshair in fullscreen mode (automatic).

OutputGLWindow.cpp

@@ -89,6 +89,10 @@ void OutputGLWindow::keyPressEvent(QKeyEvent *event)
 
 void OutputGLWindow::setFullScreen(bool fullscreen)
 {
+  // Activate crosshair in fullscreen mode.
+  setCursorVisible(!fullscreen);
+  canvas->setDisplayCrosshair(fullscreen);
+
   // NOTE: The showFullScreen() method does not work well under Ubuntu Linux. The code below fixes the issue.
   // Notice that there might be problems with the fullscreen in other OS / window managers. If so, please add
   // the code to fix those issues here.