Compound Array Problems

[tymon-pitts]

Concept:
To start I would like to explain what I'm trying to accomplish here.  I am creating a series of custom nodes that I will connect together.  
The first node in the chain is an "inluence" node.  This influence node connects into an "influenceNetwork" node that creates a
doubleArray of normalized weights for each influence node based on each one's proximity to a connected input mesh.  These weights
arrays are then plugged into my main node to drive different attributes across the surface.

Attribute Creation Code

// main node attributes
//
MFnCompoundAttribute cAttr;
flow_curves_attr = cAttr.create("flowCurves", "fwc");
 
flow_curve_weights_attr = tAttr.create("flowCurveWeights", "fwcw", MFnDoubleArrayData::kDoubleArray);
CHECK_MSTATUS(cAttr.addChild(flow_curve_weights_attr));
 
flow_curve_matrix_attr = mAttr.create("flowCurveMatrix", "fwcm");
CHECK_MSTATUS(cAttr.addChild(flow_curve_matrix_attr));
 
CHECK_MSTATUS(cAttr.setArray(true));
CHECK_MSTATUS(addAttribute(flow_curves_attr));
 
 
 
// influenceNetwork node attributes
//
normalized_weights_double_array_attr = tAttr.create("normalizedWeightsDoubleArray", "nwda", MFnDoubleArrayData::kDoubleArray);
CHECK_MSTATUS(tAttr.setKeyable(false));
CHECK_MSTATUS(tAttr.setStorable(false));
CHECK_MSTATUS(tAttr.setReadable(true));
CHECK_MSTATUS(tAttr.setWritable(false));
CHECK_MSTATUS(tAttr.setArray(true));
CHECK_MSTATUS(tAttr.setUsesArrayDataBuilder(true));
CHECK_MSTATUS(addAttribute(normalized_weights_double_array_attr));
 
 
MFnCompoundAttribute cAttr;
elements_attr = cAttr.create("elements", "e");
 
element_strength_attr = nAttr.create("elementStrength", "es", MFnNumericData::kDouble, 1.0);
CHECK_MSTATUS(cAttr.addChild(element_strength_attr));
 
element_matrix_attr = mAttr.create("elementMatrix", "em");
CHECK_MSTATUS(cAttr.addChild(element_matrix_attr));
 
CHECK_MSTATUS(cAttr.setArray(true));
CHECK_MSTATUS(addAttribute(elements_attr));
 
CHECK_MSTATUS(attributeAffects(elements_attr, normalized_weights_double_array_attr));
CHECK_MSTATUS(attributeAffects(element_strength_attr, normalized_weights_double_array_attr));
CHECK_MSTATUS(attributeAffects(element_matrix_attr, normalized_weights_double_array_attr));

Connections:
influence.strength  ->  influenceNetwork.elements[n].elementStrength
influence.worldMatrix[0]  ->  influenceNetwork.elements[n].elementMatrix

influence.worldMatrix[0]  ->  mainNode.flowCurves[n].flowCurveMatrix
influenceNetwork.normalizedWeightsDoubleArray[n]  ->  mainNode.flowCurves[n].flowCurveWeights

Problem:
I would like to have it where when an influence node is deleted, both the influenceNetwork node and my main node detect that there
is no longer a connection to the matrix child attributes and remove that multi instance of the compound array.  I searched for a way to
do this from within the api but all I found was the disconnectBehavior for a regular array attribute which won't work for my needs
because I am not connecting the array element itself. 

The solution I came up with was when my nodes compute, I test the matrix children for connections and if it is not connected I call MGlobal::executeCommand("removeMuliInstance -break true ") on that element in the array.  This worked until I connected
the output weights from the influenceNetwork into the weights child attribute of my main node.  Now it gives me this when I try to
delete one of the influence nodes:

(I am printing the command that gets run from within the nodes as well as the status that gets returned from running those commands)
removeMultiInstance -break true mainNode1Shape.flowCurves[2]
removeMultiInstance -break true influenceNetwork.elements[2]
NetworkNode::command_status = No error
MainNode::command_status = (kFailure): Unexpected Internal Failure

It also prints the following to the scriptEditor:
// Error: line 1: Unable to remove mainNode1Shape.flowCurves[2]. //

Is there any way to have a node detect that a child of a compound array element is no longer connected and remove that element of the compound array?

[joojaa]

Is there any way to have a node detect that a child of a compound array element is no longer
connected and remove that element of the compound array?

Probably not anything elegeant atleast because that would be exactly how you should not use the nodes. So nay approach you try is hack and is fighting the way maya does things. See nodes should not knowof other nodes.

Can it be done? Probably, the way i would approach this is to register an event on the deletion of the node (MDGMessage::addNodeRemovedCallback) that cleans up after the nodes gone outside of DG evaluation time. Since this event calls some command that does the cleanup its technically not the ndoes that does this and your much better isolated. Much better than trying to alter the node network in a compute cycle.

[tymon-pitts]

Thanks for the reply!

 What I'm trying to do shouldn't be too far outside the realm of what Maya already does with the disconnectBehavior of an attribute.  I'm merely trying to apply that same logic to a more complex attribute.  You are right that I probably shouldn't be doing this type of DG modification from within a compute cycle.  I didn't know about those callbacks so I will give that a try.

[tymon-pitts]

I tried Joojaa's suggestion for using MDGMessage callbacks to accomplish this and it works beautifully.  I used MDGMessage::addConnectionCallback to add the following function to the callback list:

Connection Callback

void connection_callback(MPlug& source_plug, MPlug& destination_plug, bool made, void* client_data)
{
	if (made == 0 && destination_plug == NetworkNode::element_matrix_attr)
	{
		MString command = MString("removeMultiInstance -break true ") + destination_plug.parent().name();
		MStatus command_status = MGlobal::executeCommand(command, true);
	}
}

This checks that the elementMatrix child attribute is being disconnected and removes the multi instance from the "elements" array.  I also have one of these for my main node that does the same thing (these nodes are in separate plugins so I needed different callbacks for each).  I'm using MGlobal::executeCommand here because I'm not sure that there is a better way for removing a specific element from an array.  If there is, please let me know.

 Thanks for the help!

[joojaa]

Well yes you can do it on disconnect, but that's unlike Maya normal behavior. If you only cleanup with deletion then it operates more like Maya users expect. The common way of Maya cleanup ignores cleanup if you just disconnect. As a result a common idiom is to disconnect and delete if you want to leverage on a disconnected state for some scripting task. Personally i would only act on deletion just to be nicer to power users in this regard.

  I'm using MGlobal::executeCommand here because I'm not sure that there is a better
way for removing a specific element from an array

Its the sane way of doing this yes.

[tymon-pitts]

I had moved on from this issue but now I'm coming back to it.  I'm trying to do as you suggested by doing the cleanup on delete instead of on disconnect.  The problem I'm having now is that MDGMessage::addNodeRemovedCallback seems to get called after the removal has already occured.  What I mean is that when I try to get the connections of the node being removed(via MFnDependencyNode::getConnections), there are no connections by the time it gets to the callback.