A deadlock could happen under certain circumstances when
geometry nodes is used on multiple objects.
Once T88598 is resolved, multi-threading can be enabled again.
Differential Revision: https://developer.blender.org/D11405
The old geometry nodes evaluator was quite basic and missed many features.
It was useful to get the geometry nodes project started. However, nowadays
we run into its limitations from time to time.
The new evaluator is more complex, but comes with new capabilities.
The two most important capabilities are that it can now execute nodes in
parallel and it supports lazy evaluation.
The performance improvement by multi-threading depends a lot on the specific
node tree. In our demo files, the speedup is measurable but not huge. This
is mainly because they are bottlenecked by one or two nodes that have to be
executed one after the other (often the Boolean or Attribute Proximity nodes)
or because the bottleneck is multi-threaded already (often openvdb nodes).
Lazy evaluation of inputs is only supported by the Switch node for now.
Previously, geometry nodes would always compute both inputs and then just
discard the one that is not used. Now, only the input that is required
is computed.
For some more details read D11191, T87620 and the in-code documentation.
Differential Revision: https://developer.blender.org/D11191
Those were mostly just left over from previous work on particle nodes.
They solved the problem of keeping a reference to an object over
multiple frames and in a cache. Currently, we do not have this problem
in geometry nodes, so we can also remove this layer of complexity
for now.
This is a first step towards T87620.
It should not have any functional changes.
Goals of this refactor:
* Move the evaluator out of `MOD_nodes.cc`. That makes it easier to
improve it in isolation.
* Extract core input/out parameter management out of `GeoNodeExecParams`.
Managing this is the responsibility of the evaluator. This separation of
concerns will be useful once we have lazy evaluation of certain inputs/outputs.
Differential Revision: https://developer.blender.org/D11085
