temporary fix for X Window and Windows bad canvas drawing with no single expose

Probably Item::set_position() should call Item::set_bbox_dirty() but
this will do as a first pass at that

gtk2_ardour/editor.cc

@@ -2821,7 +2821,9 @@ Editor::set_snapped_cursor_position (timepos_t const & pos)
 {
 	if (_edit_point == EditAtMouse) {
 		_snapped_cursor->set_position (pos.samples());
-		_snapped_cursor->show ();
+		if (UIConfiguration::instance().get_show_snapped_cursor()) {
+			_snapped_cursor->show ();
+		}
 	}
 }
 
@@ -6514,12 +6516,16 @@ Editor::super_rapid_screen_update ()
 			timepos_t ms (selection->markers.front()->position());
 			snap_to (ms); // should use snap_to_with_modifier?
 			_snapped_cursor->set_position (ms.samples());
-			_snapped_cursor->show ();
+			if (UIConfiguration::instance().get_show_snapped_cursor()) {
+				_snapped_cursor->show ();
+			}
 		}
 	} else if (_edit_point == EditAtMouse && mouse_sample (where.sample, ignored)) {
 		/* cursor is in the editing canvas. show it. */
 		if (!_drags->active()) {
-			_snapped_cursor->show ();
+			if (UIConfiguration::instance().get_show_snapped_cursor()) {
+				_snapped_cursor->show ();
+			}
 		}
 	} else {
 		/* mouse is out of the editing canvas, or edit-point isn't mouse. Hide the snapped_cursor */

gtk2_ardour/editor_canvas.cc

@@ -83,8 +83,12 @@ Editor::initialize_canvas ()
 
 	_track_canvas->set_background_color (UIConfiguration::instance().color ("arrange base"));
 	_track_canvas->use_nsglview (UIConfiguration::instance().get_nsgl_view_mode () == NSGLHiRes);
+#ifdef __APPLE__
+	// as of april 12 2024 on X Window and Windows, setting this to false
+	// causes redraw errors, but not on macOS as far as we can tell
 	_track_canvas->set_single_exposure (false);
-	
+#endif
+
 	/* scroll group for items that should not automatically scroll
 	 *  (e.g verbose cursor). It shares the canvas coordinate space.
 	*/

libs/canvas/tracking_text.cc

@@ -101,6 +101,7 @@ TrackingText::pointer_motion (Duple const& winpos)
 	/* move */
 
 	set_position (pos);
+	set_bbox_dirty ();
 }
 
 void