MPxNode Class Reference
[OpenMaya - API module for common classes, Proxy classes]

#include
<MPxNode.h>

Inheritance diagram for MPxNode:

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Collaboration diagram for MPxNode:

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List of all members.

Detailed Description

Base class for user defined dependency nodes.

MPxNode is the the parent class for user defined dependency nodes. A dependency node is an object that resides in the dependency graph. It computes output attributes based on a set of input attributes. When an input changes, the compute method is called for each dependent output.

The dependency graph is made up of nodes that have connections between their attributes. When an attribute changes, recomputation propagates through the graph until all affected values have been updated.

When writing a dependency node, there is a very basic rule that should be observed. The outputs should be calculated only using the values of the inputs. All information about the world outside the node should come from input attributes. If this rule is not observed, then the results may be unpredictable.

All dependency nodes have four basic attributes. Documentation for them may be found with the documentation for the dependency nodes in Maya. Only one attribute requires special attention by node developers. Developers must decide whether to support the HasNoEffect setting of the state attribute. {HasNoEffect} means that a node should pass through all data without performing computations on it. For example, a deformer node will pass geometry through unmodified when state is set to HasNoEffect. It is up the the plug-in writer to observe the HasNoEffect mode if it is relevant to the type of node.

Examples:

affectsNode.cpp, animCubeNode.cpp, anisotropicShader.cpp, apiMeshCreator.h, arcLenNode.cpp, backfillShader.cpp, blindDataMesh.h, brickShader.cpp, buildRotationNode.cpp, cellShader.cpp, cgfxShaderNode.cpp, cgfxShaderNode.h, cgfxVector.h, checkerShader.cpp, circleNode.cpp, clearcoat.cpp, closestPointOnCurveNode.h, compositingShader.cpp, contrastShader.cpp, cvColorShader.cpp, depthShader.cpp, displacementShader.cpp, exampleMRampAttribute.cpp, flameShader.cpp, fullLoftNode.cpp, gammaShader.cpp, genericAttributeNode.cpp, geomShader.cpp, GLSLShaderNode.cpp, GLSLShaderNode.h, hlslShader.cpp, hlslShader.h, interpShader.cpp, jitterNode.cpp, lambertShader.cpp, latticeNoise.h, lavaShader.cpp, lightShader.cpp, mixtureShader.cpp, multiCurveNode.cpp, noiseShader.cpp, phongShader.cpp, pointOnMeshInfoNode.h, pointOnSubdNode.h, polyModifierNode.h, renderAccessNode.cpp, shadowMatteShader.cpp, shellNode.cpp, shiftNode.cpp, simpleLoftNode.cpp, sineNode.cpp, slopeShaderNode.h, solidCheckerShader.cpp, stringFormatNode.cpp, testNobjectNode.h, testNucleusNode.h, transCircleNode.cpp, volumeShader.cpp, and weightListNode.cpp.


Public Types
enum	Type { kDependNode, kLocatorNode, kDeformerNode, kManipContainer, kSurfaceShape, kFieldNode, kEmitterNode, kSpringNode, kIkSolverNode, kHardwareShader, kHwShaderNode, kTransformNode, kObjectSet, kFluidEmitterNode, kImagePlaneNode, kParticleAttributeMapperNode, kCameraSetNode, kConstraintNode, kManipulatorNode, kLast }
	Defines the type of node. More...
Public Member Functions
	MPxNode ()
virtual	~MPxNode ()
virtual void	postConstructor ()
virtual MStatus	compute (const MPlug &plug, MDataBlock &dataBlock)
virtual bool	getInternalValueInContext (const MPlug &plug, MDataHandle &dataHandle, MDGContext &ctx)
virtual bool	setInternalValueInContext (const MPlug &plug, const MDataHandle &dataHandle, MDGContext &ctx)
virtual bool	getInternalValue (const MPlug &plug, MDataHandle &dataHandle)
	This method is obsolete.
virtual bool	setInternalValue (const MPlug &plug, const MDataHandle &dataHandle)
	This method is obsolete.
virtual int	internalArrayCount (const MPlug &plug, const MDGContext &ctx) const
virtual void	copyInternalData (MPxNode *)
virtual MStatus	legalConnection (const MPlug &plug, const MPlug &otherPlug, bool asSrc, bool &isLegal) const
virtual MStatus	legalDisconnection (const MPlug &plug, const MPlug &otherPlug, bool asSrc, bool &isLegal) const
virtual MStatus	setDependentsDirty (const MPlug &plug, MPlugArray &plugArray)
virtual MStatus	connectionMade (const MPlug &plug, const MPlug &otherPlug, bool asSrc)
virtual MStatus	connectionBroken (const MPlug &plug, const MPlug &otherPlug, bool asSrc)
virtual bool	isPassiveOutput (const MPlug &plug) const
virtual MStatus	shouldSave (const MPlug &plug, bool &isSaving)
virtual MPlug	passThroughToOne (const MPlug &plug) const
virtual bool	passThroughToMany (const MPlug &plug, MPlugArray &plugArray) const
MTypeId	typeId () const
MString	typeName () const
MString	name () const
virtual Type	type () const
virtual bool	isAbstractClass () const
MObject	thisMObject () const
MStatus	setExistWithoutInConnections (bool flag)
bool	existWithoutInConnections (MStatus *ReturnStatus=NULL) const
MStatus	setExistWithoutOutConnections (bool flag)
bool	existWithoutOutConnections (MStatus *ReturnStatus=NULL) const
Static Public Member Functions
static MStatus	addAttribute (const MObject &attr)
static MStatus	inheritAttributesFrom (const MString &parentClassName)
static MStatus	attributeAffects (const MObject &whenChanges, const MObject &isAffected)
Static Public Attributes
static MObject	message
	message attribute
static MObject	isHistoricallyInteresting
	is historically interesting attribute
static MObject	caching
	caching attribute
static MObject	state
	state attribute
Protected Member Functions
MDataBlock	forceCache (MDGContext &ctx=MDGContext::fsNormal)
	USE _forceCache() IN SCRIPT.
void	setMPSafe (bool flag)
	USE _setMPSafe() IN SCRIPT.
MStatus	setDoNotWrite (bool flag)
bool	doNotWrite (MStatus *ReturnStatus=NULL) const

Member Enumeration Documentation

enum MPxNode::Type

Defines the type of node.

Enumerator:

kDependNode	Custom node derived from MPxNode.
kLocatorNode	Custom locator derived from MPxLocatorNode.
kDeformerNode	Custom deformer derived from MPxDeformerNode.
kManipContainer	Custom container derived from MPxManipContainer.
kSurfaceShape	Custom shape derived from MPxSurfaceShape.
kFieldNode	Custom field derived from MPxFieldNode.
kEmitterNode	Custom emitter derived from MPxEmitterNode.
kSpringNode	Custom spring derived from MPxSpringNode.
kIkSolverNode	Custom IK solver derived from MPxIkSolverNode.
kHardwareShader	Custom shader derived from MPxHardwareShader.
kHwShaderNode	Custom shader derived from MPxHwShaderNode.
kTransformNode	Custom transform derived from MPxTransform.
kObjectSet	Custom set derived from MPxObjectSet.
kFluidEmitterNode	Custom fluid emitter derived from MpxFluidEmitterNode.
kImagePlaneNode	Custom image plane derived from MPxImagePlane.
kParticleAttributeMapperNode	Custom particle attribute mapper derived from MPxParticleAttributeMapperNode.
kCameraSetNode	Custom director derived from MPxCameraSet.
kConstraintNode	Custom constraint derived from MPxConstraint.
kManipulatorNode	Custom manipulator derived from MPxManipulatorNode.
kLast	Last value, used for counting.

Constructor & Destructor Documentation

MPxNode::MPxNode ( )

Constructor.

The constructor should never call any methods from MPxNode or make any calls that require the existence of the MObject associated with the user defined node. The postConstructor method should be used to do any initialization of this kind.

MPxNode::~MPxNode ( ) [virtual]

Destructor.

Member Function Documentation

void MPxNode::postConstructor ( ) [virtual]

Post constructor.

Internally maya creates two objects when a user defined node is created, the internal MObject and the user derived object. The association between the these two objects is not made until after the MPxNode constructor is called. This implies that no MPxNode member function can be called from the MPxNode constructor. The postConstructor will get called immediately after the constructor when it is safe to call any MPxNode member function.

Reimplemented in MPxPolyTrg, and MPxTransform.

Examples:

anisotropicShader.cpp, apiMeshShape.h, backfillShader.cpp, brickShader.cpp, cellShader.cpp, cgfxShaderNode.h, checkerShader.cpp, clearcoat.cpp, compositingShader.cpp, contrastShader.cpp, curvedArrowsNode.cpp, cvColorShader.cpp, depthShader.cpp, displacementShader.cpp, flameShader.cpp, gammaShader.cpp, geometrySurfaceConstraint.h, geomShader.cpp, GLSLShaderNode.h, hlslShader.h, hwAnisotropicShader_NV20.h, hwColorPerVertexShader.cpp, hwDecalBumpShader_NV20.h, hwManagedTextureShader.cpp, hwPhongShader.h, hwReflectBumpShader_NV20.h, hwRefractReflectShader_NV20.h, hwToonShader_NV20.h, hwUnlitShader.h, interpShader.cpp, lambertShader.cpp, lavaShader.cpp, lightShader.cpp, mixtureShader.cpp, noiseShader.cpp, phongShader.cpp, quadricShape.cpp, renderAccessNode.cpp, shadowMatteShader.cpp, slopeShaderNode.h, solidCheckerShader.cpp, squareScaleManipContext.h, and volumeShader.cpp.

MStatus MPxNode::compute	(	const MPlug &	plug,
		MDataBlock &	block
	)			`[virtual]`

This method should be overridden in user defined nodes.

Recompute the given output based on the nodes inputs. The plug represents the data value that needs to be recomputed, and the data block holds the storage for all of the node's attributes.

The MDataBlock will provide smart handles for reading and writing this node's attribute values. Only these values should be used when performing computations.

When evaluating the dependency graph, Maya will first call the compute method for this node. If the plug that is provided to the compute indicates that that the attribute was defined by the Maya parent node, the compute method should return MS::kUnknownParameter. When this occurs, Maya will call the internal Maya node from which the user-defined node is derived to compute the plug's value.

This means that a user defined node does not need to be concerned with computing inherited output attributes. However, if desired, these can be safely recomputed by this method to change the behaviour of the node.

Parameters:

`[in]`	plug	plug representing the attribute that needs to be recomputed
`[in]`	block	data block containing storage for the node's attributes

Returns:: Status code

Status Codes:

MS::kSuccess Compute was successful
MS::kFailure Compute failed

Reimplemented in MPxEmitterNode, MPxFieldNode, MPxFluidEmitterNode, MPxParticleAttributeMapperNode, MPxPolyTrg, and MPxTransform.

Examples:

affectsNode.cpp, animCubeNode.cpp, anisotropicShader.cpp, apiMeshCreator.h, apiMeshShape.h, arcLenNode.cpp, backfillShader.cpp, blindDataMesh.h, blindDataShader.h, brickShader.cpp, buildRotationNode.cpp, cellShader.cpp, cgfxShaderNode.h, cgfxVector.h, checkerShader.cpp, circleNode.cpp, clearcoat.cpp, closestPointOnCurveNode.h, compositingShader.cpp, contrastShader.cpp, curvedArrowsNode.cpp, cvColorNode.cpp, cvColorShader.cpp, depthShader.cpp, displacementShader.cpp, exampleMRampAttribute.cpp, flameShader.cpp, footPrintManip.cpp, footPrintNode.cpp, fullLoftNode.cpp, gammaShader.cpp, genericAttributeNode.cpp, geometrySurfaceConstraint.h, geomShader.cpp, GLSLShaderNode.h, hwColorPerVertexShader.cpp, hwDecalBumpShader_NV20.h, hwPhongShader.h, hwReflectBumpShader_NV20.h, hwRefractReflectShader_NV20.h, hwToonShader_NV20.h, hwUnlitShader.h, interpShader.cpp, jitterNode.cpp, lambertShader.cpp, latticeNoise.h, lavaShader.cpp, lightShader.cpp, mixtureShader.cpp, multiCurveNode.cpp, noiseShader.cpp, phongShader.cpp, pointOnMeshInfoNode.h, pointOnSubdNode.h, quadricShape.cpp, renderAccessNode.cpp, shadowMatteShader.cpp, shellNode.cpp, shiftNode.cpp, simpleLoftNode.cpp, simpleSpring.h, sineNode.cpp, slopeShaderNode.h, solidCheckerShader.cpp, stringFormatNode.cpp, swissArmyManip.cpp, testNobjectNode.h, testNucleusNode.h, transCircleNode.cpp, volumeShader.cpp, and weightListNode.cpp.

bool MPxNode::getInternalValueInContext	(	const MPlug &	plug,
		MDataHandle &	dataHandle,
		MDGContext &	ctx
	)			`[virtual]`

This method is overriden by nodes that store attribute data in some internal format.

The internal state of attributes can be set or queried using the setInternal and internal methods of MFnAttribute.

When internal attribute values are queried via getAttr or MPlug::getValue this method is called.

NOTE: the default behaviour of this method is to call MPxNode::getInternalValue( const MPlug&, const MDataHandle& ) if the context is normal.

Parameters:

`[in]`	plug	the attribute that is being queried
`[out]`	dataHandle	the dataHandle to store the attribute value
`[in]`	ctx	the context the method is being evaluated in

Returns:

true the attribute was place on the datablock
false could not handle the specified attribute, pass this request to the default handler

Examples:

cgfxShaderNode.h, customImagePlane.cpp, GLSLShaderNode.h, hlslShader.h, hwColorPerVertexShader.cpp, and hwPhongShader.h.

bool MPxNode::setInternalValueInContext	(	const MPlug &	plug,
		const MDataHandle &	dataHandle,
		MDGContext &	ctx
	)			`[virtual]`

This method is overriden by nodes that store attribute data in some internal format.

The internal state of attributes can be set or queried using the setInternal and internal methods of MFnAttribute.

When internal attribute values are set via setAttr or MPlug::setValue this method is called.

Another use for this method is to impose attribute limits.

NOTE: the default behaviour of this method is to call MPxNode::setInternalValue( const MPlug&, const MDataHandle& ) if the context is normal.

Parameters:

`[in]`	plug	the attribute that is being set
`[in]`	dataHandle	the dataHandle containing the value to set
`[in]`	ctx	the context the method is being evaluated in

Returns:

true the attribute was set
false could not handle the specified attribute, pass this request to the default handler

Examples:

cgfxShaderNode.h, customImagePlane.cpp, GLSLShaderNode.h, hlslShader.h, hwColorPerVertexShader.cpp, and hwPhongShader.h.

bool MPxNode::getInternalValue	(	const MPlug &	plug,
		MDataHandle &	dataHandle
	)			`[virtual]`

This method is obsolete.

Deprecated:: Use the method MPxNode::getInternalValueInContext instead.

This method is overriden by nodes that store attribute data in some internal format.

Examples:

apiMeshShape.cpp, apiMeshShape.h, cgfxShaderNode.cpp, hlslShader.cpp, pnTrianglesNode.h, and quadricShape.cpp.

bool MPxNode::setInternalValue	(	const MPlug &	plug,
		const MDataHandle &	dataHandle
	)			`[virtual]`

This method is obsolete.

Deprecated:: Use the method MPxNode::setInternalValueInContext instead.

This method is overriden by nodes that store attribute data in some internal format.

Examples:

apiMeshShape.cpp, apiMeshShape.h, cgfxShaderNode.cpp, hlslShader.cpp, pnTrianglesNode.h, and quadricShape.cpp.

int MPxNode::internalArrayCount	(	const MPlug &	plug,
		const MDGContext &	ctx
	)			const `[virtual]`

This method is overriden by nodes that have internal array attributes which are not stored in Maya's datablock. This method is used by Maya to determine the non-sparse count of array elements during file io. If the internal array is stored sparsely, you should return the maximum index of the array plus one. If the internal array is non-sparse then return the length of the array.

This method does not need to be implemented for attributes that are stored in the datablock since Maya will use the datablock size.

If this method is overriden, it should return -1 for attributes which it does not handle. Maya will use the datablock size to determine the array length when -1 is returned.

Parameters:

`[in]`	plug	the array plug
`[in]`	ctx	the context

void MPxNode::copyInternalData ( MPxNode * node ) [virtual]

This method is overriden by nodes that store attribute data in some internal format.

On duplication this method is called on the duplicated node with the node being duplicated passed as the parameter. Overriding this method gives your node a chance to duplicate any internal data you've been storing and manipulating outside of normal attribute data.

Parameters:

[in] node the node that is being duplicated

Reimplemented in MPxTransform.

Examples:

cgfxShaderNode.h, GLSLShaderNode.h, and hlslShader.h.

MStatus MPxNode::legalConnection	(	const MPlug &	plug,
		const MPlug &	otherPlug,
		bool	asSrc,
		bool &	isLegal
	)			const `[virtual]`

This method allows you to check for legal connections being made to attributes of this node.

You should return kUnknownParameter to specify that maya should handle this connection if you are unable to determine if it is legal.

Parameters:

`[in]`	plug	attribute on this node
`[in]`	otherPlug	attribute on other node
`[in]`	asSrc	is this plug a source of the connection
`[in]`	isLegal	set this to true if the connection is legal, false otherwise

Returns:: Status code

Status Codes:

MS::kSuccess Operation successful
MS::kUnknownParameter Unknown attribute

MStatus MPxNode::legalDisconnection	(	const MPlug &	plug,
		const MPlug &	otherPlug,
		bool	asSrc,
		bool &	isLegal
	)			const `[virtual]`

This method allows you to check for legal disconnections being made to attributes of this node.

You should return kUnknownParameter to specify that maya should handle this disconnection if you are unable to determine if it is legal.

Parameters:

`[in]`	plug	attribute on this node
`[in]`	otherPlug	attribute on other node
`[in]`	asSrc	is this plug a source of the connection
`[out]`	isLegal	set this to true if the disconnection is legal, false otherwise

Returns:: Status code

Status Codes:

MS::kSuccess Operation successful
MS::kUnknownParameter Unknown attribute

MStatus MPxNode::setDependentsDirty	(	const MPlug &	plugBeingDirtied,
		MPlugArray &	affectedPlugs
	)			`[virtual]`

This method can be overridden in user defined nodes to specify which plugs should be set dirty based upon an input plug {plugBeingDirtied} which Maya is marking dirty. The list of plugs for Maya to mark dirty is returned by the plug array {affectedPlugs}. This method handles both dynamic as well as non-dynamic plugs and is useful in the following ways:

Allows attributeAffects-style relationships to be handled for dynamically-added attributes. Since MPxNode::attributeAffects can only be used with non-dynamic attributes, use of this method allows a way for all attributes of a node to affect one another, both dynamic and non-dynamic.

Provides more flexible relationships than what is available with MPxNode::attributeAffects. For example, you may wish to not dirty plugs when the current frame is one. However, as the routine is called during dirty propagation, there are restrictions on what can be done within the routine, most importantly you must not cause any dependency graph computation. For details, see the IMPORTANT NOTE below.

This method is designed to work harmoniously with MPxNode::attributeAffects on the same node. Alternately, you can do all affects relationships within a yourNode::setDependentsDirty() implementation.

The body of a user-implemented setDependentsDirty() implementation might look like the following example, which causes the plug called "B" to be set dirty whever plug "A" is changed, i.e. A affects B.

    const   MString exampleNode::A( "A" );  // Dynamic attribute "A"
    MObject exampleNode::attrB;     // Non-dynamic attribute "B"

    MStatus exampleNode::setDependentsDirty(
            const MPlug &plugBeingDirtied,
            MPlugArray &affectedPlugs )
    {
        // This example shows a dynamic attribute (A) affecting a
        // non-dynamic attribute (B). For an example of a dynamic
        // affecting a dynamic, please the the developer's toolkit
        // example plug-in, affectsNode.cpp.
        //
        if ( plugBeingDirtied.partialName() == A ) {
            // "A" is being dirtied. We want "A" to affect "B", so we
            // add "B" to the list of plugs for Maya to dirty. Once again,
            // please see the IMPORTANT NOTE about what you can and
            // cannot do within a setDependentsDirty() routine.
            //
            MObject thisNode = thisMObject();
            MPlug pB( thisNode, exampleNode::attrB );
            affectedPlugs.append( pB );
        }
        return( MS::kSuccess );
    }

In the above example, whenever plugBeingDirtied is A, we add B to affectedPlugs so that Maya will dirty B and also any plugs which depend upon B.

For cases where multi compound attributes are dirtied, it is the programmer's responsibility to define ALL affects relationships. Dirtying the parent plug of a multi does not imply that all of its children will be marked dirty. Likewise, dirtying a child attribute does not imply the parent of the multi is dirty. This must be explicitly defined using the affected plug array. The following example demonstrates how one would dirty both the element affected and the parent plug.

    MObject exampleNode::inputAttr;     // Non-dynamic multi-input attribute.
    MObject exampleNode::outputAttr;    // Non-dynamic multi-output attribute.
    MStatus exampleNode::setDependentsDirty(MPlug const & inPlug,
                                            MPlugArray  & affectedPlugs)
    {
        if ( inPlug.attribute() != inputAttr ) {
            return MS::kSuccess;
        }

        MPlug outArrayPlug(thisMObject(),outputAttr);

        if (inPlug.isElement()) {
            // First dirty the output output element first.
            // Of course, dirty output element itself
            MPlug elemPlug = outArrayPlug.elementByLogicalIndex(
                                                inPlug.logicalIndex());
            affectedPlugs.append(elemPlug);

            // We also need to dirty the parent.
            //
            affectedPlugs.append(outArrayPlug);
        } else {
            // Mark the parent output plug as dirty.
            //
            affectedPlugs.append(outArrayPlug);

            // Also visit each element.
            //
            unsigned int i,n = outArrayPlug.numElements();
            for (i = 0; i < n; i++) {
                MPlug elemPlug = outArrayPlug.elementByPhysicalIndex(i);
                affectedPlugs.append(elemPlug);
            }
        }
        return MS::kSuccess;
    }

IMPORTANT NOTE: since the setDependentsDirty() method is called during dirty propagation, you must be careful not to perform any dependency graph computations from within the routine. Instead, if you want to know the value of a plug, use MDataBlock::outputValue() because it will not result in computation (and thus recursion). In general, the majority of {setDependentsDirty()} methods which users will implement should involve only fixed relationships. In the rare occurence where you need to look at plug values, please heed the warning with {MDataBlock::outputValue()} and use plugs which contain values which you know to be up to date prior to the start of dirty propagation.

Parameters:

`[in]`	plugBeingDirtied	plug which is being set dirty by Maya
`[in]`	affectedPlugs	the programmer should add any plugs which they want to set dirty to this list.

Returns:: Status code

Status Codes:

MS::kSuccess Dirtying was successful
MS::kFailure Dirtying failed

Examples:

affectsNode.cpp.

MStatus MPxNode::connectionMade	(	const MPlug &	plug,
		const MPlug &	otherPlug,
		bool	asSrc
	)			`[virtual]`

This method gets called when connections are made to attributes of this node.

You should return kUnknownParameter to specify that maya should handle this connection or if you want maya to process the connection as well.

Parameters:

`[in]`	plug	attribute on this node
`[in]`	otherPlug	attribute on other node
`[in]`	asSrc	is this plug a source of the connection

Returns:: Status code

Status Codes:

MS::kSuccess Operation successful
MS::kUnknownParameter Unknown attribute

Examples:

apiMeshShape.cpp, apiMeshShape.h, and GLSLShaderNode.h.

MStatus MPxNode::connectionBroken	(	const MPlug &	plug,
		const MPlug &	otherPlug,
		bool	asSrc
	)			`[virtual]`

This method gets called when connections are broken with attributes of this node.

You should return kUnknownParameter to specify that maya should handle this connection or if you want maya to process the connection as well.

Parameters:

`[in]`	plug	attribute on this node
`[in]`	otherPlug	attribute on other node
`[in]`	asSrc	is this plug a source of the connection

Returns:: Status code

Status Codes:

MS::kSuccess Operation successful
MS::kUnknownParameter Unknown attribute

Examples:

apiMeshShape.cpp, apiMeshShape.h, and GLSLShaderNode.h.

bool MPxNode::isPassiveOutput ( const MPlug & plug ) const [virtual]

This method may be overridden by the user defined node if it wants to provide output attributes which do not prevent value modifications to the destination attribute. For example, output plugs on animation curve nodes are passive. This allows the attributes driven by the animation curves to be set to new values by the user.

Parameters:

[in] plug plug representing output in question

Returns:: true indicates passive

MStatus MPxNode::shouldSave	(	const MPlug &	plug,
		bool &	isSaving
	)			`[virtual]`

This method may be overridden by the user defined node. It should only be required to override this on rare occasions.

This method determines whether a specific attribute of this node should be written out during a file save. The default behavior is to only write the value if it differs from the default and is not being supplied by a connection. This behavior should be sufficient in most cases. This method is not called for ramp attributes since they should always be written.

Parameters:

`[in]`	plug	plug representing the attribute to be saved
`[in]`	isSaving	boolean telling whether to save or not

Returns:: Status code

Status Codes:

MS::kSuccess Operation successful
MS::kUnknownParameter Unknown attribute

Examples:

apiMeshShape.cpp, apiMeshShape.h, cgfxShaderNode.cpp, and cgfxShaderNode.h.

MPlug MPxNode::passThroughToOne ( const MPlug & plug ) const [virtual]

This method may be overriden by nodes that have a one-to-one relationship between an input attribute and a corresponding output attribute. This method is used by Maya to perform the following capabilities:

When this node is deleted, the delete command will rewire the source of the input attribute to the destination of the output attribute if the source and destination are connected to nodes that are not deleted.
History traversal algorithms such as the bakePartialHistory command use this method to direct its traversal through a shape's construction history.
The base class Maya implementation of passThroughToAll will call this method if passThroughToAll returns false.

Parameters:

[in] plug the plug

Returns:: The corresponding plug, or an empty plug if no corresponding plug exists

bool MPxNode::passThroughToMany	(	const MPlug &	plug,
		MPlugArray &	plugArray
	)			const `[virtual]`

This method is overriden by nodes that want to control the traversal behavior of some Maya search algorithms which traverse the history/future of shape nodes looking for directly related nodes. In particular, the Artisan paint code uses this method when searching for paintable nodes, and the disk cache code uses this method when searching for upstream cacheFile nodes.

If this method is not implemented or returns false, the base class Maya implementation of this method calls passThroughToOne and returns the results of that call.

Parameters:

`[in]`	plug	the plug
`[in]`	plugArray	the corresponding plugs

Returns:: true if plug was handled, false to invoke base class implementation

MTypeId MPxNode::typeId ( ) const

Returns the TYPEID of this node. The TYPEID is a four byte identifier that uniquely identifies this type of node to the binary file format.