Mdagmodifier Vs Mdgmodifier

[yunjun]

Hey, when I want to create a node (createNode), which class should I use, MDagModifer or MDGModifier?

Thanks.

[daniel-faust]

if you just want to add a dependency node then use the MDGModifier, if you want to add a DAG node, then use the MDagModifier.

MDagModifier is a more complex version of the MDGModifier (it's derived from it, as you can see in the docs), which has the added ability to position the new node in the DAG structure (parenting and reparenting is added)

MDagModifier:: createNode:
"This method adds an operation to this DAG modifier that will add a new node of the given type to the DAG. This method may not be used to construct new dependency graph nodes that are not in the DAG. Use MDGModifier for that purpose."

[yunjun]

thanks, Daniel_Faust,

if I want to create a curveVarGroup, should I use the MDGModifier?

I did the following, but the returned stat is false.

MObject curveVarGObj =dgMod.createNode("curveVarGroup",&stat);

However, when I did:
MObject intersectSurfaceNodeObj = dgMod.createNode( "intersectSurface", &stat);
the returned stat is true.

i don't see much difference between the two, while only one is working.

[daniel-faust]

go into the documentation of the nodes:

If you take a look at the curveVarGroup you are provided with the following info:
Node name Parents MFn type Compatible function sets
curveVarGroup baseGeometryVarGroup kCurveVarGroup kBase
kNamedObject
kDependencyNode // <-------------------- this indicates that it is a dependency node
kDagNode // <-------------------- this indicates that it is a DAG node, so you must use the MDagModifier
kTransform
kGeometryVarGroup
kCurveVarGroup

The docs on the intersectSurface tell you
Node name Parents MFn type Compatible function sets
intersectSurface abstractBaseCreate kIntersectSurface kBase
kNamedObject
kDependencyNode // <-------------------- this indicates that it is a dependency node
kCreate
kIntersectSurface
but you can't find any info on kDagNode. So this is a plain dependecy node and you must use the MDGModifier

A DAG node is a dependency node which is not only located inside the dependency graph, but also in the DAG.

[yunjun]

You are right, I changed the code to:

MDGModifier dgMod;
MObject intersectSurfaceNodeObj = dgMod.createNode( "intersectSurface", &stat);

MDagModifier dagMod;
MObject curveVarGNode =dagMod.createNode("curveVarGroup", MObject::kNullObj, &stat);

dgMod.connect(.....)

both createNode functions returned stat as true and seem to be successful. however, the newly created nodes are not shown in the HyperGraph Scene Hierarchy, neither are the connections shown.

Am I missing something here? Much appreciated.

[daniel-faust]

yes you need to call the do() or doIt() (cant remember) method of the modifiers. But you are not done with that. you need to take care of calling the undo and redo mehtod at the correct times (go figure...). Those modifiers are a real blessing since they help you a lot wiht the undo redo functionality, but you still need to do the necessary work to call those two methods. it is not trivial.

I cannot remember where I found a great tutorial which implemented the undo / redo functionality with the help of std::vector containers. You need to do undo/redo since you are modifying the dg and/or dag. this is important, else you will cause maya to crash (if lucky) oder get into an unstable state which is something you must avoid.

I believe it was a tutorial from ewert.com or s.th. like that (site is down), or davidgould. but you might get lucky with robthebloke.org theres a lot of good stuff there.

Else you might want to call MGlobal::executeCommand("createNode ......", true, true); (that is undo true), so that the mel command engine will take care of undoing the node's creation when needed.

[yunjun]

Daniel_Faust,

Thank you so much for your advice on the undo/redo routine. I will spend more time on that. Currently, I just added a MDGModigier dgMod.doIt(); at the end of my doIt() and it seems Maya is trying to create the node for me. (I think I am too beginner to write the undo/redo code so I set my command to be undoable at the moment).

When it comes to connections, I am still having the problem.

MGlobal::getActiveSelectionList( selection );
MItSelectionList iter( selection );
iter.setFilter(MFn::kGeometric);
for ( iter.reset(); !iter.isDone(); iter.next() )
{
MObject objShapeNode;
stat = iter.getDependNode (objShapeNode);
if( stat )
{
MFnDependencyNode objDepNodeFn(objShapeNode);
MObject intersectSurfaceNode = dgMod.createNode( "intersectSurface", &stat);
MFnDependencyNode interSecDepNodeFn (intersectSurfaceNode);
MStatus stat2;
stat = dgMod.connect(objDepNodeFn.findPlug("worldSpace[0]", &stat2 ), interSecDepNodeFn.findPlug("inputSurface1"));
}
}
[/code]

there is an error at the dgMod.connect line: (both stat and stat2 returned false).
Error: Connection not made: '' -> 'intersectSurface1.inputSurface1'. Data types of source and destination are not compatible.

I looked into the documentation and think maybe I need to create a nurbsSurface node from the selected object rather than just using MFnDependencyNode. But I don't have an idea of how. Are you by any chance familiar with this?
Thanks a lot!

[daniel-faust]

QUOTE
(I think I am too beginner to write the undo/redo code so I set my command to be undoable at the moment).

No, this is not a solution. If your command modifies the DG (and it does!), then you MUST implement undo/redo.

Regarding the other problem, I believe the kGeometric implies that the node is also compatible with kDagNode and therefore a dag node.

You are using iter.getDependNode(objShapeNode); to retrieve a dag node from the selection list iterator. This will not do. You must use iter.getDagPath(objShapeNode); if you want to retrieve a dag node.

See iter.itemType to check of your're dealing with a kDagSelectionItem and therefore should use getDagPath or if your'Re dealing with a kDNselectionItem and therefore should use getDependNode (since plain dependency nodes don't have a dag path). But anyway, you're filtering your selection to kDagNodes (which I _believe_ contains kGeometry as a subset) so you should not be encountering plain dependency nodes and therefore you should not need to use getDependNode at all.

Do not check for (stat != 0) to see if retrieveing the node succeeded, but use (stat == MStatus::kSuccess) instead. This is because
CODE
class OPENMAYA_EXPORT MStatus
{

public:

    /// Available Status Codes
    enum MStatusCode
    {
        /// The operation was successful
        kSuccess = 0,
        /// The operation failed
        kFailure,
        /// The operation failed due to insufficient memory
        kInsufficientMemory,
        /// An invalid parameter was provided
        kInvalidParameter,
        /// Application is not licensed for the attempted operation
        kLicenseFailure,
        /// Returned by MPxNode::compute for unrecognised plugs
        kUnknownParameter,
        /// Not currently used
        kNotImplemented,
        /// Not currently used
        kNotFound,
        /// Not currently used
        kEndOfFile
    };

defines that kSuccess = 0, and therefore (stat == 0) or (!stat) is succeeding. So you are checking for failure if your're checking for (stat).

So you see that actually getDependNode has been failing all the time and therefore objShapeNode and objDepNodeFn are invalid. this means that objDepNodeFn.findPlug("worldSpace[0]") will fail and thus the connection can't be made.

The only lesson you can take from this is that you should always check return values (MStatus), and check them against the enum (MStatus::kSucceeded or MStatus::kFailed).

Also, you really must implement undo/redo.

[yunjun]

Thank you! I will try to implement the undo/redo function. Now I am making a bit of progress by using the MFnDagNode (I am still confused with dag/dependency node and will do more reading):

CODE
stat=iter.getDagPath( dagPath, component );
MFnDagNode shapeFn( dagPath );

MPlug plug1 = shapeFn.findPlug( "worldSpace", &stat);
stat = dgMod.connect(plug1, interSecDepNodeFn.findPlug("inputSurface1"));

MPlug plug2 = shapeFn.findPlug( "worldSpace[0]", &stat);
stat = dgMod.connect(plug2, interSecDepNodeFn.findPlug("inputSurface1"));

in the code, the feedback to the scriptor editor when I run the code:

the first dgMod.connect produces the error:
// Error: Connection not made: 'nurbsSphereShape1.worldSpace' -> 'intersectSurface1.inputSurface1'. Incompatible multi-attribute parent levels. //

the second dgMod.connect:
// Error: Connection not made: '' -> 'intersectSurface2.inputSurface1'. Data types of source and destination are not compatible. //

I think this is because the nurbsSurface node ->attribute "worldSpace" is an array, do you know how I can extract the first element of the array and use it to connect? Thanks!

[yunjun]

To get the elements of the plugArray, I tried the PlugArray.elementByLogicalIndex and it works. However, I don't know what's happening behind the scene of this Logical Index, since I tried to do

MIntArray logIndices;
PlugArray.getExistingArrayAttributeIndices(logIndices);

the returned logIndices always has 0 elements. while at the same time, the elementByLogicalIndex(0) returns the right thing.
But still, I need to retrieve all the elements in the array by the logical index so that I can get all the curves from the curveVarGroup (see my code below), which are resulted from the intersection.

CODE

stat=iter.getDagPath( dagPath, component );
MFnDagNode shapeFn( dagPath );
MPlug plug1Array = shapeFn.findPlug( "worldSpace", &stat);
MPlug plug1;
if (plug1Array.isArray())
    plug1 = plug1Array.elementByLogicalIndex(0, &stat);

MObject intersectSurfaceNode = dgMod.createNode( "intersectSurface", &stat);
MFnDependencyNode interSecDepNodeFn (intersectSurfaceNode);

stat = dgMod.connect(plug1, interSecDepNodeFn.findPlug("inputSurface1"));
. . . . .  //until here it all works

stat = dgMod.connect(interSecDepNodeFn.findPlug("output3dCurve"),curveVarGNodeFn.findPlug("create"));
MPlug localPlugArray = curveVarGNodeFn.findPlug("local",&stat);    
if (localPlugArray.isArray())
{
    MIntArray logIndices;
    localPlugArray.getExistingArrayAttributeIndices(logIndices);
    int log = logIndices.length();//here, the length is always 0
    for (unsigned int i = 0;i<logIndices.length();i++)
    {
        . . . . .
    }
}