Previously, the data-block dependencies were always detected in
`update_depsgraph` in `MOD_nodes.cc`. This would only be called when something
called `DEG_relations_tag_update` before. We don't want to trigger a depsgraph
rebuild after each operation in the node editor, as that would be expensive.
However, that also meant that we often had to add data-block dependencies that
are not actually used, but might be used if the user changed e.g. a link. A
typical example for that is a object socket that has a default value, but the
socket is also linked.
Now, the dependencies referenced by the node tree are collected by the node tree
update code which runs after all changes. This way we can detect whether the
dependencies have changed. Only if they have changed, a depsgraph rebuild is
triggered. This now allows also taking into account the mute status of nodes and
whether an input is linked.
There are still more things that could be taken into account. Most obviously
whether a node is connected to an output. This can be done later. The most
tricky aspect here is probably that we also have to consider all viewer nodes as
output, because at the time the node runs, it's not known which viewer will
actually be used (which depends on other editors).
This also cleans up some special cases we had for e.g. the scene time node where
we always had to trigger a depsgraph rebuild when it was added/removed because
of its time dependence. This is now part of a more general system.
This fixes#109219.
Pull Request: https://projects.blender.org/blender/blender/pulls/131446
b36bf15e28