python/api1/py1ArrayAttrBlenderNode.py

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#
# Autodesk Script File
# MODIFY THIS AT YOUR OWN RISK
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# Creation Date:   27 May 2021
#

"""
  DESCRIPTION:

  Implements the dependency graph node "spArrayAttrBlend".  

  This plug-in is an example of a user-defined dependency graph node.
  It takes 2 array inputs and it computes an array output
  where each output value is the average of the 2 corresponding inputs values. 
  A weight parameter controls how much of input A vs input B is taken into 
  account in the output computation
 
    // Create a spArrayAttrBlend connected to a cube translation
    createNode spArrayAttrBlend;
    polyCube;
 
    connectAttr spArrayAttrBlend1.output[0] pCube1.tx;
    connectAttr spArrayAttrBlend1.output[1] pCube1.ty;
    connectAttr spArrayAttrBlend1.output[2] pCube1.tz;
 
    // Modify input parameters to affect the cube position
    setAttr spArrayAttrBlend1.weight 1; // Output is driven 100% by inputB
    setAttr spArrayAttrBlend1.inputB[1] 10; // will feed 10 to pCube1.ty
 
"""

import maya.OpenMaya as OpenMaya
import maya.OpenMayaMPx as OpenMayaMPx

kPluginNodeTypeName = "spArrayAttrBlend"
kPluginNodeId = OpenMaya.MTypeId(0x0008005A)


# Node definition
class spArrayAttrBlend(OpenMayaMPx.MPxNode):
    
    # Node Type Attributes
    aInputA = OpenMaya.MObject()
    aInputB = OpenMaya.MObject()
    aWeight = OpenMaya.MObject()
    aOutput = OpenMaya.MObject()


    def __init__(self):
        OpenMayaMPx.MPxNode.__init__(self)


    def getInputValue( data, attribute, logicalIndex ):
        """
        Helper method that extract an element value from the datablock for a specified
        array attribute
        """
        # This code was extracted from the compute method because it needs to be executed twice 
        # at each evaluation (once for each input)

        arrayDataHandle = data.inputArrayValue( attribute )
        try:
            arrayDataHandle.jumpToElement( logicalIndex )
            value = arrayDataHandle.inputValue().asFloat()
        except:         
            # Extracting Attribute default value
            # Code is compled because MFnNumericAttribute returns its result through a reference 
            # parameter which ends up being very complicated to handle in Python API1
            default_util = OpenMaya.MScriptUtil()
            default_util.createFromDouble(0.0)
            default_ptr = default_util.asFloatPtr()
            OpenMaya.MFnNumericAttribute( attribute ).getDefault( default_ptr )
            value = default_util.getFloat( default_ptr )

        return value
        
    
    def compute(self, plug, data):
        """
        This callback gets invoked when Maya needs to retrieve the value of 
        a marked dirty plug
        """

        # Check that the requested recompute is one of the output values
        if (plug == spArrayAttrBlend.aOutput ):
            if plug.isArray():
                # full attribute is rarely queried but by returning kUnknownParameter
                # we ensure Maya default implementation will trigger the evaluation of 
                # each element of the array plug
                return OpenMaya.kUnknownParameter
            else:
                # Computing the value of one array plug element
                logicalIndex = plug.logicalIndex()

                # Read the input values
                A = spArrayAttrBlend.getInputValue( data, spArrayAttrBlend.aInputA, logicalIndex )
                B = spArrayAttrBlend.getInputValue( data, spArrayAttrBlend.aInputB, logicalIndex )

                weight =  data.inputValue( spArrayAttrBlend.aWeight ).asFloat()

                blendedValue = A*(1.0-weight )+B*weight

                data.outputValue(plug).setFloat( blendedValue )
                data.setClean( plug )
                return None
        else:
            return OpenMaya.kUnknownParameter


    def setDependentsDirty( self, plug, plugArray ):
        # this method is optional. It currently handles the dependence of output on inputA and inputB
        # This approach differs from letting Maya doing the dirtying based on the MPxNode.attributeAffects
        # because it defines a plug element to plug element relationship. MPxNode.attributeAffects usage 
        # would cause a dirtying of all the output elements even for a single input element change
        if (plug == spArrayAttrBlend.aInputA ) or (plug == spArrayAttrBlend.aInputB ):
            if plug.isElement():
                logicalIndex = plug.logicalIndex()
                thisNode = self.thisMObject()
                outPlug = OpenMaya.MPlug( thisNode, spArrayAttrBlend.aOutput )
                outPlug.selectAncestorLogicalIndex( logicalIndex, spArrayAttrBlend.aOutput )
                plugArray.append(outPlug)


# creator
def createNodeInstance():
    """ Maya invokes this method everytime it needs to instanciate a spArrayAttrBlend node """
    return OpenMayaMPx.asMPxPtr( spArrayAttrBlend() )


# initializer
def initNodeTypeAttributes():
    """
    This method is invoked when spArrayAttrBlend node type gets registered
    allowing the current plugin to register and setup attributes to the 
    new spArrayAttrBlend type
    """

    # The MFnNumericAttribute will help in the creation of all the numerical 
    # input and output attributes
    nAttr = OpenMaya.MFnNumericAttribute()

    # Setup the input attributes
    spArrayAttrBlend.aInputA = nAttr.create("inputA", "ia", OpenMaya.MFnNumericData.kFloat, 0.2)
    nAttr.setStorable(True)
    nAttr.setArray( True )

    spArrayAttrBlend.aInputB = nAttr.create("inputB", "ib", OpenMaya.MFnNumericData.kFloat, 0.3)
    nAttr.setStorable(True)
    nAttr.setArray( True )

    spArrayAttrBlend.aWeight = nAttr.create("weight", "wt", OpenMaya.MFnNumericData.kFloat, 0.5)
    nAttr.setStorable(True)
    nAttr.setArray( False )

    # Setup the output attributes
    spArrayAttrBlend.aOutput = nAttr.create("output", "out", OpenMaya.MFnNumericData.kFloat, 0.0)
    nAttr.setStorable(False)
    nAttr.setWritable(False)
    nAttr.setArray( True )

    # Add the attributes to the node
    spArrayAttrBlend.addAttribute(spArrayAttrBlend.aInputA)
    spArrayAttrBlend.addAttribute(spArrayAttrBlend.aInputB)
    spArrayAttrBlend.addAttribute(spArrayAttrBlend.aWeight)
    spArrayAttrBlend.addAttribute(spArrayAttrBlend.aOutput)

    # Set the attribute dependencies
    spArrayAttrBlend.attributeAffects(spArrayAttrBlend.aWeight, spArrayAttrBlend.aOutput)

    # The following dependencies should not be declared because they are already handled 
    # by the optional setDependentsDirty method
    # spArrayAttrBlend.attributeAffects(spArrayAttrBlend.aInputA, spArrayAttrBlend.aOutput)
    # spArrayAttrBlend.attributeAffects(spArrayAttrBlend.aInputB, spArrayAttrBlend.aOutput)


def initializePlugin(mobject):
    """ This method is automatically invoked when the plugin is loaded """
    mplugin = OpenMayaMPx.MFnPlugin(mobject, "Autodesk", "1.0", "Any")
    try:
        mplugin.registerNode( kPluginNodeTypeName, kPluginNodeId, createNodeInstance, initNodeTypeAttributes )
    except:
        sys.stderr.write( "Failed to register node: %s" % kPluginNodeTypeName )
        raise


def uninitializePlugin(mobject):
    """ This method is automatically invoked when the plugin is unloaded """
    mplugin = OpenMayaMPx.MFnPlugin(mobject)
    try:
        mplugin.deregisterNode( kPluginNodeId )
    except:
        sys.stderr.write( "Failed to deregister node: %s" % kPluginNodeTypeName )
        raise