Before the scene composition is created, render layer compositions in the scene composition are created or updated.
With a Template If a template is specified for the scene, its content is copied into the scene composition and the rest of the operations applied to it are quite similar to what happens during an update of the scene.
The dependency graph is reviewed to find all the render layer anchor link nodes which are updated to link to their associated render layer composition, which was previously created or updated.
If some render layer anchor link nodes are missing in the scene template, new unconnected render layer link nodes are automatically added to the scene composition (in the same way as when no template is specified).
Without a Template If no scene template is specified, render layer anchor link nodes are created with their proper anchor name set and point to their respective render layer composition. Render layers are then stacked in a chain of Blend and Comp nodes, respecting the compositing order and blend modes used in the 3D scene.
What Happens Next? The render layer link nodes have their anchors automatically set to their corresponding render layer anchor name and the nodes are initially named after their linked render layer compositions (their names are not changed by further updates).
The image format, pixel format, and the rate of the scene composition are then set according to the default render settings of the 3D scene. The time range (start, end) of the scene composition is then set to the union of its render layer compositions time ranges.
A scene composition is updated when a new layer is added to the scene. Deleting a layer will not trigger an update because it's non-destructive. Renaming a layer is equivalent to adding a new layer.
The working version of the scene 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).
Existing render layer anchor link nodes are left unchanged because they point to the latest version of the render layer composition by default. The ones that are missing are created and linked to their respective render layer compositions.
If an existing render layer is no longer in the scene (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 scene composition update is non-destructive—see Non-Destructive Updates.
If the layer ordering or the blend modes between layers have changed, a new stack of Blend & Comp nodes is created within a visual group next to the old stack. In the following example, the tire and tire label layers were added during update.
The format and rate of a scene composition is not modified on update. However, the start/end of the scene composition is updated to be the union of its current time range and the time ranges of all its linked render layer compositions.
