The issue was that the code did not handle input sockets that are fields
implicitly correctly. It just retrieved a single from them, instead of
treating them as having an unknown value.
This builds on top of 80441190c6 to gray output
unused inputs of the Mix and Mix Shader node. These nodes have unused inputs if
their mix factor is 0 or 1 (+ some special cases for non-uniform vector mixing
and blend modes).
Pull Request: https://projects.blender.org/blender/blender/pulls/133369
This patch automatically grays out input values which can't affect the output
currently. It works with inputs of group nodes, geometry nodes modifiers and
node tools.
To achieve this, it analyses the node tree and partially evaluates it to figure
out which group inputs are currently not linked to an output or are disabled by e.g.
some switch node.
Original proposal: https://devtalk.blender.org/t/dynamic-socket-visibility/31874
Related info in blog post:
https://code.blender.org/2023/11/geometry-nodes-workshop-november-2023/#dynamic-socket-visibility
Follow up task for designing a UI that allows hiding sockets: #132706
Limitations:
* The inferencing does not update correctly when a socket starts being
animated/driven. I haven't found a good way to invalidate the cache in a good
way reliably yet. It's only a very short term problem though. It fixes itself
after the next modification of the node tree and is only noticeable when
animating some specific sockets such as the switch node condition.
* Whether a socket is grayed out is not exposed in the Python API yet. That will
be done separately.
* Only a partial evaluation is done to determine if an input affects an output.
There should be no cases where a socket is found to be unused when it can actually
affect the output. However, there can be cases where a socket is inferenced to be used
even if it is not due to some complex condition. Depending on the exact circumstances,
this can either be improved or the condition in the node tree should be simplified.
Pull Request: https://projects.blender.org/blender/blender/pulls/132219
