Just wanted to know, maybe a very dumb question, but would in a theory
Feedback Layers / Scene node be possible ?
I found myself having to convert scenes / layers to images just for that. Plus, image has limited borders that make negative feedbacks look ugly (squares, image edges visible).
Yes, and you're welcome to create a feature request for it.
There would be different ways to go about it, depending on how you wanted to handle the limited borders.
One way would be to add a Wrap Mode input port to the existing
Blend Image with Feedback node. It would let you specify what happens outside the feedback image: None (current behavior), or Clamp, Repeat, Mirrored Repeat. This wouldn't show the actual layers/objects that were outside the borders, but would avoid the abrupt edges.
Another way would be to add new nodes
Add Feedback to Layers and
Add Feedback to Scene. These would input a list of layers / 3D objects instead of an image. As you fed in a series of layer/object lists into the node over time, it would store them up in the node and use them to compute the feedback. The node would output a grouped layer/object to be passed to
Render Layer/Scene to Window. This would contain the most recent layers/objects plus progressively faded-out versions of the previous layers/objects. It would be more computation-heavy than the first option, but would provide correct results for layers/objects beyond the borders.
There's a third way to reduce edge artifacts for limited borders, which you could do right now without a feature request — apply
Blend Image with Feedback to a larger rendered area than you ultimately want, then crop it.