This patch allows the compositor context to specify exactly which
outputs it needs, selecting from: Composite, Viewer, File Output, and
Previews. Previously, the compositor fully executed if any of those were
needed, without granular control on which outputs are needed exactly.
For the viewport compositor engine, it requests Composite and Viewer,
with no Previews or File Outputs.
For the render pipeline, it requests Composite and File Output, with
node Viewer or Previews.
For the interactive compositor, it requests Viewer if the backdrop is
visible or an image editor with the viewer image is visible, it requests
Compositor if an image editor with the render result is visible, it
requests Previews if a node editor has previews overlay enabled. File
outputs are never requested.
Pull Request: https://projects.blender.org/blender/blender/pulls/133960
e53ac805af