Introduction to Maya презентация

Biography Naiqi Weng -- Autodesk Developer Network Education Bachelor of Computer Science Master of Computer Science Working experience Supporting software: Maya API, MotionBuilder SDK and 3dsMax SDK

Dependency Graph

Agenda What is Dependency Graph (DG)? Concepts/Elements of DG Nodes Custom plug-in DG node with Maya API DG’s push-pull mechanism Correct coding with DG

Maya Hypergraph Menu: “Window”– “Hypergraph:Connections”

What is the Dependency Graph? Control system of Maya Patented technology: US Patent #5,808,625 US Patent #5,929,864 A collection of nodes that transmit data through connected attributes

Dependency Graph Everything in Maya 3D space maps to DG Nodes Anything you do in the UI will affect DG

Dependency Graph

What does a node do? Know its own attributes Store data efficiently in “datablocks” Accept input data, compute, generate output data Connect with other nodes through connections

Different elements of a Node

Attributes Describe data that belongs to nodes of a given type Attributes are shared among nodes of the same type and all derived node types

Attributes Define the interface of the node type including Names Data Type Basic: numeric (float, int32 etc…), string, matrix, etc.. Complex: mesh, nurbsSurface, generic, etc… Custom data Structure Properties readable, writable, storable, keyable, etc…

API Classes for Attributes Base Class: MFnAttribute Takes care of all the common aspect of an attribute on node readable/writable, connectable, storable, keyable Most Common Used Classes MFnNumericAttribute MFnCompoundAttribute MFnTypedAttribute MFnMatrixAttribute MFnGenericAttribute

Different elements of a Node

Plugs Pointer to an attribute on a specific node (ie. a specific instance of an attribute)

Plugs Plugs can be used to: query / set a value create / remove /query a connection Does not store attribute data API class: MPlug MPlug::MPlug (const MObject &node, const MObject &attribute) MObject MPlug::attribute ( MStatus *  ReturnStatus)  MObject MPlug::node ( MStatus *  ReturnStatus)  MStatus MPlug::getValue ( double &  val, MDGContext &  ctx ) MStatus MPlug::setValue ( double  val  ) 

Different elements of a Node

Datablock Node stores data for every attribute

Datablocks Datablock is the actual storage for the input and output data of a node For every non-array attribute, datablock stores: Data Dirty/clean status Data handles are lightweight pointers into the data in the datablock

API Classes for datablock MDatablock Only valid during compute() Pointers to data block should not be retained after compute() MStatus MPxNode::compute(const MPlug& plug, MDataBlock& dataBlock) MDataHandle MDataBlock::inputValue(const MObject& attribute, MStatus *  ReturnStatus) MDataHandle MDataBlock::outputValue ( const MObject & attribute, MStatus *  ReturnStatus) MDataHandle a smart pointer for information contained in data block double & MDataHandle::asDouble (  )  void MDataHandle::set( double  val  ) 

Custom Node Plug-in Implementation

Custom DG Node in Maya Entirely new operations MPxNode: base class for custom node implementation Extend existing Maya nodes MPxDeformerNode MPxFieldNode MPxEmitterNode MPxSpringNode MPxIkSolverNode MPxHwShaderNode

Custom Node Code Skeleton class myNode : public MPxNode { public: myNode(); virtual ~myNode(); static void* creator(); static MStatus initialize(); virtual MStatus compute( const MPlug& plug, MDataBlock& data ); private: static MTypeId id; static MObject myInputAttr; //input attribute static MObject myOutputAttr; //output attribute static MObject myOutputAttrTwo; //second output attribute };

Custom Node Registration Every node type requires a unique identifier MTypeId myNode::id( 0x80000 ); For plug-ins that you intend to share between sites Will require a globally unique ID issued to you by Autodesk. IDs are allocated in blocks of 64/128/256/512. Contact ADN M&E for unique global IDs.

Custom Node Registration initializePlugin() and uninitializePlugin() are entry point and exit point of custom plug-in node

Custom Node Registration To register your node with Maya: To deregister your node

Custom Node Code Skeleton MPxNode::creator() The creator method is called to return a new instance of the node In the Maya UI MEL: createNode myNode;

Custom Node Code Skeleton MPxNode::initialize() Override this method to define the attribute interface for your node. create attributes set the attribute’s properties add the attribute to the node Inherit attributes if necessary define attribute relationships

Attribute Dependency Attributes can affect other attributes MEL command: affects sphere -n sphere; affects tx sphere; MPxNode::attributeAffects() Once created on a node, an “attributeAffects” relationship can be setup to denote a dependency

Custom Node Code Skeleton

Custom Node Code Skeleton MPxNode::compute() called when the node is asked to evaluate an output

Examples Devkit Plug-in Examples: C:\Program Files\Autodesk\Maya2011\devkit\plug-ins The Maya API Documentation contains a wealth of information on all aspects of the API.

How does Dependency Graph work? Control system for Maya Glue that holds together disparate operations and lets them work together seamlessly DG is not a usual dataflow system….

How does Dependency Graph Work? Two step Push-Pull mechanism: Dirty Propagation Evaluation

Dirty Propagation Maya DG caches values Uses dirty system to denote elements that require updating: Attributes Connections MEL Commands: dgdirty isDirty

Data Flow Example Key

The Dirty Process Initiated by value changes

The Dirty Process Dirty message propagates forward

The Dirty Process No evaluation has been requested. Data remains dirty.

The Dirty Process Now an input on A changes

The Dirty Process Dirty propagates out all outgoing connections

The Dirty Process B and D propagate dirty to affected attributes C will not receive dirty message Connection to C is already dirty Helps performance

The Evaluation Process Lazy Evaluation: On demand Evaluation is trigged when values are requested: Viewport refresh Attribute editor Channel box Rendering getAttr command Etc… Evaluation is minimal Only requested values are computed Non-requested values are left dirty

The Evaluation Process Example: getAttr C.output

The Evaluation Process C computes: requests input value from connection

The Evaluation Process D computes. D requests input value from connection

The Evaluation Process A computes requested output

The Evaluation Process Value copied forward to D’s input

The Evaluation Process D computes requested result. D sets value in output.

The Evaluation Process Value is copied forward to C

The Evaluation Process C computes requested output. B remains dirty.

The Evaluation Process Only requested outputs are computed, unless node’s compute method does more than requested

Correct Coding with DG

Correct Coding with DG Common misuse: put command-type tasks into a custom node implementation execute commands to change the status of current DG get or set values on other nodes Black Box Rule

Black Box Rule Black-box operation of node is what makes it all work.

A Closer Look at MPxNode::compute() You can not control when compute() is getting called, Maya control when it gets called Compute() is called in Evaluation phase Inside compute(): avoid sending dirty messages Don’t execute commands Don’t get or set values on other nodes

A Closer Look at MPxNode::compute() Inside compute(): avoid sending dirty messages Get/set data only through datablock using data handles, don’t set data via plugs (i.e. MPlug::setValue) setting data via plug propagates dirty, datahandle does not datahandle set/get methods are more efficient

Learning Resources Maya Developer Center: http://www.autodesk.com/developmaya Questions and Problems: ADN http://www.autodesk.com/adn Maya API White Paper, DevTV, Webcast training Discussion Forum: The AREA http://area.autodesk.com/forum/autodesk-maya/sdk/

Q & A

Thank you!