Render Layer Composition Creation
Before the render layer composition is created, render pass compositions for the given render layer are created or updated.
With a Template If a template is specified for the render layer, its content is copied into the render layer composition and the rest of the operations applied to it are quite similar to what happens during an update.
The dependency graph is reviewed to find all the render pass anchor link nodes which are updated to link to their associated render pass composition, which was previously created or updated.
If some render pass anchor link nodes are missing in the template, new unconnected render pass anchor link nodes are automatically added to the render layer composition (in the same way as when no template is specified).
Without a Template If no template is specified, the render layer composition is created with a single unconnected output node. For each render pass composition, there is an unconnected link node that points to it.
The render pass link nodes have their anchors automatically set to their corresponding render pass anchor name and the nodes are initially named after their linked render pass compositions (their names are not changed by further updates).
What Happens Next? By default, a render pass anchor link node points to the Latest version. This is because a new render pass composition version was added during a pre-comp file update is not automatically tagged as the primary version. Choosing the primary render pass version is up to you. If you want the render layer composition to be updated automatically when new Maya render passes are imported in Composite, the render pass anchor link nodes must point to their latest version by default—see Working with CompositionsWorking with Compositions.
The image format, pixel format and rate of the render layer composition are set according to the information contained in the pre-comp file.
The time range (start, end) of the render layer composition is then set to the union of its render pass compositions time ranges.
Render Layer Composition Update
A render layer composition is updated when a new pass is added to the scene. Deleting a pass will not trigger an update because it's non-destructive. Renaming a pass is equivalent to adding a new pass.
The working version of the render layer composition is backed up if you set the Backup Version option. Then, in Update mode, the working version is updated. otherwise it is recreated from scratch (Recreate mode).
Updating the render layer composition is then quite straightforward. Existing render pass anchor link nodes are left unchanged because they point to the latest version of the render pass composition by default. The ones that are missing are created (but are unconnected) and linked to their respective render pass compositions.
If an existing render pass is no longer in the render layer (which could be because it was removed from the 3D scene or because the pre-comp file update is partial), its anchor link node is not deleted; the render layer composition update is non-destructive—see Non-Destructive Updates.
The format and rate of a render layer composition is not modified on update. However, the start/end of the render layer composition is updated to be the union of its current time range and the time ranges of all its linked render pass compositions.
