Editor: Render cell markers
In PagedWorldspaceWidget scenes each cell needs to be represented by a marker. This could either be a cube or maybe a billboard in the centre of the cell. It might be a good idea to render these above all actual content, since otherwise they may be hidden by the terrain or other objects. These markers will be used later to manipulate the cell as a whole. Since we have unused space on the surface of these markers, we should use it to display the cell coordinates.
- The marker need to be added/removed automatically as the selection of rendered cells changes.
- Some of the rendered cells may not exist (yet). That is okay, but it is important that the rendering code does not try to access the cell records. It should work purely with the information stored in the PagedWorldspaceWidget.
- The markers need a separate visibility flag, so that they can be switched on/off from the scene toolbar (button not implemented yet).
- When rendered the markers should always be included in mouse picking queries.
- We need a method to match marker objects to the cells they represent. Encoding this information in the OGRE handle seems the easiest method, but there may be other options.
(RM-1281 from redmine: created on 2014-04-14 by Marc Zinnschlag, , closed on 2014-10-17 by gus gus, relates #3043 (closed))