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Maya dependency nodes have 6 possible states.
The Normal (0), HasNoEffect (1), and Blocking (2) states can be
used to alter how the graph is evaluated.
The Waiting-Normal (3), Waiting-HasNoEffect (4), Waiting-Blocking (5)
are for internal use only. They temporarily shut off parts of the graph during interaction
(e.g., manipulation). The understanding is that once the operation is done,
the state will be reset appropriately, e.g. Waiting-Blocking will reset
back to Blocking.
The Normal and Blocking cases apply to all nodes, while
HasNoEffect is node specific; many nodes do not support this option.
Plug-ins store state in the MPxNode::state attribute. Anyone can set
it or check this attribute. Additional details about each of these 3 states follow.
| State |
Description |
| Normal |
The normal node state. This is the default. |
| HasNoEffect |
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.
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| Blocking |
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.
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Default: kdnNormal
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