Setting Material Overrides using Look Files

Following the core principle in Katana that all scene data should be inspectable and modifiable, mechanisms are needed to allow material settings defined in Look Files to be overridable downstream.

In Katana this is done by bringing the materials into the scene so that the user can use the normal Katana nodes, such as the Material node in 'override' mode, so make changes.

For efficiency, and to avoid lighters scenes becoming littered with every single material that may be used on any asset in the scene, the materials used in by a Look File aren't loaded into scenes by default. If you want to set overrides on the materials you first need to use a LookFileOverrideEnable node. This brings in the materials from the Look File into the Katana scene and sets them up (by bringing them in a specific locations in the scene graph hierarchy based on the name of the Look File) so that these instances are used instead of the ones contained in the original Look File.

LookFileOverrideEnable also brings in any renderer procedurals for overriding in a similar manner to materials.