Dagpath from a MFnData::kMesh attribute

[holixxx]

I'm writing a node where I've got a MFnData::kMesh attribute as input (called inputMesh). My trouble is I can't seem to get a DAG path to this input mesh.

In the compute method I do this:

MDagPath dagPath

MDataHandle inMeshDataHandle = data.inputValue(inputMesh);

MObject meshObj = inMeshDataHandle.asMesh();

MFnMesh meshFn(meshObj);

meshFn.getPath(dagPath);

but getPath fails, telling me the object does not exist! The function set can read it fine, i.e. tell me how many edges the mesh has got etc, so why can't I get the path!? Please, does someone know what I'm doing wrong? This is driving me crazy!!

[hohehohe2]

Basically a mesh node(DAG node) and a mesh data is different. See
5 Dependency Graph Plug-ins - A more complex example
of the API manual.

[cyril-romain]

I have the same problem of retriving a dag path or the name of an input mesh in my compute (or deform) methods.

Basically a mesh node(DAG node) and a mesh data is different.

Ok, this explain the "why" of the problem.

But I'm looking for the "how" answer :
How to retrieve a dag path (for example) from the input mesh ?
I looked at the API manual : "more complex example" but I didn"t find the answer.

[hohehohe2]

A mesh data is only a data, not a dag node. Only dag nodes have
a dag path. So there is no dag path for a mesh data.
It's just like no double3 value has a dag path.

[holixxx]

ok, I know that it is a mesh data.
but my question is quite simple: how can I retrieve the mesh node from this mesh data ?

thanks in advance

[hohehohe2]

I don't exactly know what you are doing. If you just want to
visualize the data, you can put it to an output attribute,
(maybe after doing some modification in your compute() method)
then create a mesh node and connect the output to the inmesh attribute of the mesh node.
You cannot get infomation like cv positions (in the world coordinate)
from it since the mesh data is not yet placed in the scene.
Is it what you are looking for?

[cyril-romain]

Hi,

The only way I found to do such a thing in a "compute" or "deform" method is to access the mesh node from the upstream connection of the current node :

MFnDependencyNode fnDNode( thisMObject() );

MPlug inputMeshPlug = fnDNode.findPlug( "myInputMeshAttribute" );

MPlugArray inputPlugArray;

inputMeshPlug.connectedTo(inputPlugArray, true, false );

MObject inputNode = inputPlugArray[0].node();

if ( inputNode.hasFn( MFn::kMesh ) )
{
	MFnDagNode fnDAGN( inputNode );
	MDagPath meshDagPath;
	fnDAGN.getPath( meshDagPath );
	cout << "The full DAG Path of the input mesh: " << meshDagPath.fullPathName() << endl;
}

But I think there must be a better way to do it ...
Does anyone have a better solution ?

[hohehohe2]

Okey. If the mesh data is the output of an upstream mesh node, it will work.
I think in many cases it will do. Thanks.
I think it is a neat way.

[swimwdolphin]

Hi Cyril_Romain, and others who are interested,

I have similar problem and tried the method you mentioned but when I try
to create a function set FnDependency on the kMeshData MObject, the constructor of the function
set fails saying that the object is incompatiable...

I'm crazy now, like the original poster of this problem...
There must be some "magic" behind the function set
APIs...

Thank you for your advice in advance,
Swimwdolphin.
p.s. Please see the code below for details.

initialize()
{
aInMesh = fnTyped.create( "inMesh", "inm", MFnMeshData::kMesh );
addAttribute( aInMesh );
}

compute()
{
//...

// inMesh
MDataHandle hMesh = block.inputValue( aInMesh );

//
MObject moMesh = hMesh.asMesh();
m\_pFnMesh = new MyMayaFnMesh( moMesh, &status );

if ( !moMesh.hasFn(MFn::kMesh) )		//ok
	::MayaPrint(">>> hasFn(MFn::kMesh) fails at .n");
if ( !moMesh.hasFn(MFn::kMeshData) )		//ok
	::MayaPrint(">>> hasFn(MFn::kMeshData) fails at .n");

MFnMesh* fnMesh = new MFnMesh(moMesh, &status);
if ( status != MS::kSuccess ) //ok
{
	::MayaPrint(">>> FnMesh::FnMesh(aInMesh) fails: %s n", status.errorString().asChar() ) ; 
}
delete fnMesh;


MFnDependencyNode * fnMesh2 = new 	MFnDependencyNode (moMesh, &status);
if ( status != MS::kSuccess ) //**ERROR**
{ 
	::MayaPrint(">>> FnD::FnDaInMesh) fails: %s n", status.errorString().asChar() ) ; 
}

//
MPlug plug = fnNode.findPlug( "inMesh", &status );

// ...

delete fnMesh2;

}