Overlays allow multiple scene references without the risk of creating circular dependencies.
The scene XRef marked as overlay is loaded only into the master scene that references it, and is not visible in other scenes that might XRef the master file that uses the overlay. Consider two scenes that reference each other:
Ordinarily, 3ds Max would recognize this as a circular dependency, and disallow it. However, you can set up such a combination of XRefs by following these steps:
- In scene 2, XRef scene 1 and use the toggle to flag it as an overlay.
- Save scene 2.
- Open scene 1, and XRef scene 2.
Scene 2 is externally referenced into scene 1, without pulling scene 1 in as a nested external reference.
The previous example is not particularly practical. But suppose you want to mask off part of your scene so other artists who XRef the scene will not see it. For example, you are working on a building and have XRefed a CAD file that lays out the plumbing of the building, as well as a scene of ground terrain that contains some XRefs to some trees. The XRef scene graph might look like this:
The building scene XRefs the terrain and the plumbing data. The terrain scene XRefs the trees. You decide you are the only one who needs to see the CAD plumbing data. The CAD plumbing data is needed only to line up where the sinks need to be in the building, so you set up the CAD plumbing data XRef to be an overlay. Other scenes that include the building scene won’t see the plumbing. For example, another artist who is responsible for the lighting and cameras sets up an XRef to the building scene. Now the XRef graph looks like this:
In this case, an overlay is used to simply hide data information from other master scenes. Another use of overlays is to avoid circular XRefs. For example, picture four artists working on a scene of a city block. Two of them are working on individual buildings, one is working on a sky bridge that connects the two buildings, and the fourth artist is setting up the cameras and the lights. The graph of externally referenced scenes might look like this:
But the artists working on Building A and the artist working on the sky bridge need to see each other’s work to make sure everything lines up. The obvious solution would be to externally reference each other’s scene file:
However, 3ds Max detects a circular external reference and won’t allow this, unless both the Building A scene and the Sky Bridge scene flag their external reference as an Overlay.
