Introduction to Maya

Biography

Naiqi Weng -- Autodesk Developer Network
Education
Bachelor of Computer Science
Master

Dependency Graph

Agenda

What is Dependency Graph (DG)?
Concepts/Elements of DG Nodes
Custom plug-in DG

Maya Hypergraph

Menu: “Window”– “Hypergraph:Connections”

Nodes

Node

Connections

Attributes

Connections

What is the Dependency Graph?

Control system of Maya
Patented technology: US Patent

Dependency Graph

Everything in Maya 3D space maps to DG Nodes
Anything you

Dependency Graph

© 2009 WET, Artificial Mind and Movement (now Behaviour

Dependency Graph

New Type Custom Node

What does a node do?

Know its own attributes
Store data efficiently in

Different elements of a Node

Maya Node

Attributes

Plugs

DataBlock
DataHandle

Attributes

Describe data that belongs to nodes of a given type
Attributes are

Attributes

Define the interface of the node type including
Names
Data Type
Basic: numeric (float,

API Classes for Attributes

Base Class: MFnAttribute
Takes care of all the

Different elements of a Node

Maya Node

Attributes

Plugs

DataBlock
DataHandle

Plugs

Pointer to an attribute on a specific node (ie. a specific

Plugs

Plugs can be used to:
query / set a value
create / remove

Different elements of a Node

Maya Node

Attributes

Plugs

DataBlock
DataHandle

Datablock

Node stores data for every attribute

Datablock

Node

Attribute

Datablocks

Datablock is the actual storage for the input and output data

API Classes for datablock

MDatablock
Only valid during compute()
Pointers to data block should

Maya Node

Attributes

Plugs

DataBlock
DataHandle

MPxNode

MFnAttribute

MPlug

MDataBlock
MDataHandle

Custom Node Plug-in Implementation

Custom DG Node in Maya

Entirely new operations
MPxNode: base class for custom

Custom Node Code Skeleton

class myNode : public MPxNode
{
public:
myNode();
virtual

Custom Node Registration

Every node type requires a unique identifier
MTypeId

Custom Node Registration

initializePlugin() and uninitializePlugin() are entry point and exit point

Custom Node Registration

To register your node with Maya:
To deregister your node

MStatus

Custom Node Code Skeleton

MPxNode::creator()
The creator method is called to return a

Custom Node Code Skeleton

MPxNode::initialize()
Override this method to define the attribute interface

Attribute Dependency

Attributes can affect other attributes
MEL command: affects
sphere -n sphere;
affects

Custom Node Code Skeleton

MStatus myNode::initialize()
{
MFnNumericAttribute nAttr;
myInputAttr = nAttr.create(“myInput”, “mi”,

Custom Node Code Skeleton

MPxNode::compute()
called when the node is asked to evaluate

Examples

Devkit Plug-in Examples:
C:\Program Files\Autodesk\Maya2011\devkit\plug-ins
The Maya API Documentation contains a wealth of

How does Dependency Graph work?

Control system for Maya
Glue that holds together

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

Data Flow Example

Key

= clean connection,

= dirty connection

A

B

D

C

E

The Dirty Process

Initiated by value changes

setAttr D.r 5;

A

B

D

C

E

The Dirty Process

Dirty message propagates forward

A

B

D

C

E

The Dirty Process

No evaluation has been requested. Data remains dirty.

A

B

D

C

E

The Dirty Process

Now an input on A changes

setAttr A.aIn 6

A

B

D

C

E

The Dirty Process

Dirty propagates out all outgoing connections

A

B

D

C

E

The Dirty Process

B and D propagate dirty to affected attributes
C will

The Evaluation Process

Lazy Evaluation: On demand
Evaluation is trigged when values are

The Evaluation Process

Example: getAttr C.output

A

B

D

C

getAttr c.output

E

The Evaluation Process

C computes: requests input value from connection

?

A

B

D

C

E

The Evaluation Process

D computes.
D requests input value from connection

?

A

B

D

C

E

The Evaluation Process

A computes requested output

A

B

D

C

E

The Evaluation Process

Value copied forward to D’s input

A

B

D

C

E

The Evaluation Process

D computes requested result.
D sets value in output.

A

B

D

C

E

The Evaluation Process

Value is copied forward to C

A

B

D

C

E

The Evaluation Process

C computes requested output.
B remains dirty.

A

B

D

C

E

The Evaluation Process

Only requested outputs are computed, unless node’s compute method

Correct Coding with DG

Correct Coding with DG

Common misuse:
put command-type tasks into a custom

Black Box Rule

Black-box operation of node is what makes it all

A Closer Look at MPxNode::compute()

You can not control when compute() is

A Closer Look at MPxNode::compute()

Inside compute(): avoid sending dirty messages
Get/set data

Learning Resources

Maya Developer Center:
http://www.autodesk.com/developmaya
Questions and Problems: ADN
http://www.autodesk.com/adn
Maya API White Paper,

Q & A