polyPoke

The HasNoEffect option (a.k.a. pass-through), is used in cases where there is an operation on an input producing an output of the same data type. Nearly all deformers support this state, as do a few other nodes. As stated earlier, it is not supported by all nodes.

It’s typical to implement support for the HasNoEffect state in the node’s compute method and to perform appropriate operations. Plug-ins can also support HasNoEffect.

The usual implementation of this state is to copy the input directly to the matching output without applying the algorithm in the node. For deformers, applying this state leaves the input geometry undeformed on the output.

This is implemented in the depend node base class and applies to all nodes. Blocking is applied during the evaluation phase to connections. An evaluation request to a blocked connection will return as failures, causing the destination plug to retain its current value. Dirty propagation is indirectly affected by this state since blocked connections are never cleaned.

When a node is set to Blocking the behavior is supposed to be the same as if all outgoing connections were broken. As long as nobody requests evaluation of the blocked node directly it won’t evaluate after that. Note that a blocked node will still respond to getAttr requests but a getAttr on a downstream node will not reevaluate the blocked node.

Setting the root transform of a hierarchy to Blocking won’t automatically influence child transforms in the hierarchy. To do this, you’d need to explicitly set all child nodes to the Blocking state.

For example, to set all child transforms to Blocking, you could use the following script.

import maya.cmds as cmds
def blockTree(root):
nodesToBlock = []
for node in {child:1 for child in cmds.listRelatives( root, path=True, allDescendents=True )}.keys():
nodesToBlock += cmds.listConnections(node, source=True, destination=True )
for node in {source:1 for source in nodesToBlock}.keys():
cmds.setAttr( '%s.nodeState' % node, 2 )

Applying this script would continue to draw objects but things would not be animated.