Get "real" Vertex Order In A Mesh

[seith]

I'm looking for a way to find the "real" vertex order in a mesh. I know it's easy to just get the number of vertices (from 0 to whatever), but I'm interested in the order that Maya stores them internally. Those are two different things. For example, if you do...

CODE
ls -fl polyListComponentConversion -tv pCube1f[0]

... you'll get the list of vertices belonging to the face 0 of pCube1. But if you do a...

CODE
polyInfo -fv pCube1.f[0]

... Then you'll get the list of vertices in creation order (the order they have to be to form the face), which is very different.

Basically I'm looking for the same thing, but for the vertices in a mesh. I found out that the API command MFnMesh::getVertices will do exactly that, but I don't know anything about c++, so I need help to access this information from MEL or Python...

[visualfx]

This will give you access to the MFnMesh::getVertices() method. You need to supply the 'mesh' argument as the string name of the actual mesh shape node! You could easily add in the ability to get the shape from a transform input if you needed to...

CODE
import maya.cmds as mc
import maya.OpenMaya as OpenMaya

def getVertices(mesh):

    mc.select(mesh)
    selList = OpenMaya.MSelectionList()
    OpenMaya.MGlobal.getActiveSelectionList(selList)
    meshObj = OpenMaya.MObject()
    selList.getDependNode(0,meshObj)

    meshFn = OpenMaya.MFnMesh( meshObj )

    meshVtxCount = OpenMaya.MIntArray()
    meshVtxArray = OpenMaya.MIntArray()

    meshFn.getVertices(meshVtxCount,meshVtxArray)

    vtxList = []
    for i in range(meshVtxArray.length()):
        vtxList.append(meshVtxArray[i])

    return vtxList

[seith]

That's fantastic! Thanks Visualfx. I didn't know you could access API commands from Python by importing the appropriate module.

Now actually I'm puzzled by the result, as in the case for a simple poly cube (pCubeShape1) the procedure tells me that there are 6 vertices (?!) in "meshVtxCount" and gives me a list of 24 vertices index (??!!) in "meshVtxArray", instead of a count of 8 and a list of 8 elements...

What am I doing wrong?

[rob-bateman]

use getPoints() which will give you 8 elements. the data you have right now is the poly counts, and vert indices. for a cube, these could be:

CODE
// six faces, each with 4 verts
meshVtxCount = { 4,4,4,4,4,4 }  

// 24 elements, which is the same as the sum of all 6 meshVtxCount
// elements. the first 4 relate to the indices of the first face.
// meshVtxCount[0] says face 0 has 4 vertex indices.
meshVtxArray = { 0,1,2,3, .... }

After triangulation, this would look more like:

CODE
// 12 faces, each with 3 verts
meshVtxCount = { 3,3,3,3,3,3,3,3,3,3,3,3 }  

// 36 elements, i.e. 12 * 3
meshVtxArray = { 0,1,2, .... }

you could also import the MItMeshPolygon class and use that to iterate over the faces instead. It will also give you the correct ordering of the vertices. See http://www.robthebloke.org/research/maya/mfnmesh.htm

[seith]

Thanks Rob! So I tried using getPoint instead, and indeed I get a list of 8 elements (the 8 the vertices of the cube, I assume), but it spits them in a "weird" format that I don't know how to use:

CODE
[<maya.OpenMaya.MPoint; proxy of >, <maya.OpenMaya.MPoint; proxy of >, <maya.OpenMaya.MPoint; proxy of >, <maya.OpenMaya.MPoint; proxy of >, <maya.OpenMaya.MPoint; proxy of >, <maya.OpenMaya.MPoint; proxy of >, <maya.OpenMaya.MPoint; proxy of >, <maya.OpenMaya.MPoint; proxy of >]

So my (probably silly) question is: how do I get the actual index number of those vertices...?

[visualfx]

If you are after vertex indices, getPoints() is not going to tell you what you want to know. The getPoints() method returns an array of MPoints describing the position of each individual vertex, which is the source of the weird formatting you mentioned.
What the getVertices() method is returning is an array of faceVertex counts ("meshVtxCount", ie. number of verts per face) and a list of faceVertex indices ("meshVtxArray")...where the faceVertex indices are given as object-relative index values (as opposed to face-relative indices).

You mentioned that for a simple cube "meshVtxCount" was returning 6. I would assume that is the number of elements in the array (cube = 6 faces), accessed by meshVtxCount.length(). Each of those 6 elements should have been 4.