Maya API 小筆記

Node　（Class）
Attribute　（Field)
Compute　（Member Function)

DG：Denpendency Graph
(Horizontal view, input and output connection between different nodes)

DAG：Directed Acyclic Graph
(Vertical view, Hierarchy, ex. transformation -> shape)

DAG is a DG

MDagPath (Hierarchy info of node, you can manipulate geometry in world coordinate space)
MObject (Handle to node, you just can manipulate geometry in object coordinate space)

Push-Pull Approach
Push: forward propogate the message which updating each child node's flag(dirty bit).
Pull: backward propogate the message which updating each parent node's status.
updating: updating, execute each node's compute function, DAG Path from root to child.
(共三趟)

dirty data：通常指資料已被改變(如：在記憶體內的data)，但尚未write back(如：在硬碟的檔案系統)。

MPxNode:

xxxCmd.cpp (network view)
	virtual MStatus	doIt ( const MArgList& );
	virtual MStatus undoIt();
 	virtual MStatus redoIt();
	virtual bool isUndoable() const { return true; }

	static void *creator() { return new MeltCmd; }

　　特別是在doIt()利用MPlug來存取場景中所有node的attribute, 並建立node與node之間的連結.
　　(MPlug xxPlug = xxxFn.findPlug("xxx");
　　(利用MDagModifier或MDgModifier 的connect(), disconnect(),createNode())

　　ex:
　　　MFnDependencyNode nodeFn(obj);
　　　MPlug xPlg = nodeFn.findPlug("translateX");
　　　double tx;
　　　xPlg.getValue(tx);          //get an attribute at current time.
　　　MTime t(1.5, MTime::kSeconds);
　　　MDGContext ctx(t);
　　　transxPlug.getValue(tx, ctx);    //get an attribute at specific time.

xxxNode.cpp (node view)
　　virtual MStatus compute(MPlug &plug, MDataBlock &data ){
　　　　利用MDataHandle來存取data, (data.inputVaule(), data.outputValue()),
　　　　並計算output attribute的值.
　　}

　　static  MStatus initialize(){
　　　　利用MFnXXAttribue 來初始attribute,
　　　　addAttribute();
　　　　attributeAffects();     //建立node中attribute的互動關係.
　　}

　　static  void *creator();
　　static const MTypeId id;

MPxLocatorNode:

    virtual void draw( M3dView &; view, const MDagPath &path,
　　　　　　　　M3dView::DisplayStyle style, M3dView::DisplayStatus status );
    virtual bool isBounded() const;
    virtual MBoundingBox boundingBox() const;
    static void *creator();
    static MStatus initialize();

MPxCommand:

	virtual MStatus	doIt ( const MArgList&);
	virtual MStatus undoIt();
 	virtual MStatus redoIt();
	virtual bool isUndoable() const { return true; }
	static void *creator() { return new MeltCmd; }