[Maya] get adjacent vertices to a vertex

Simple scripts to get the first ring of neighborhood of a vertex of a mesh in Maya.

MEL procedures

string $selectedVertices[] = `ls -selection -flatten`;

// Convert the selected vertices to vertex faces
string $vertexFaces[] = `polyListComponentConversion -fromVertex -toVertexFace $selectedVertices`;

// Convert the vertex faces to vertices (this will give adjacent vertices)
string $adjacentEdges[] = `polyListComponentConversion -fromVertexFace -toEdge $vertexFaces`;

// Convert the edges to vertices (this will give adjacent vertices)
string $adjacentVertices[] = `polyListComponentConversion -fromEdge -toVertex $adjacentEdges`;

$adjacentVertices = `ls -flatten $adjacentVertices`;

//select $adjacentVertices;
// Filter out the original selected vertices from the adjacent vertices list
string $adjacentVerticesFiltered[] = `stringArrayRemove $selectedVertices $adjacentVertices`;
select $adjacentVerticesFiltered;

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Less conservative version:

string $selectedVertices[] = `ls -selection -flatten`;

// Convert the selected vertices to vertex faces
string $faces[] = `polyListComponentConversion -fromVertex -toFace $selectedVertices`;

// Convert the edges to vertices (this will give adjacent vertices)
string $adjacentVertices[] = `polyListComponentConversion -fromFace -toVertex $faces`;

$adjacentVertices = `ls -flatten $adjacentVertices`;

//select $adjacentVertices;
// Filter out the original selected vertices from the adjacent vertices list
string $adjacentVerticesFiltered[] = `stringArrayRemove $selectedVertices $adjacentVertices`;
select $adjacentVerticesFiltered;

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Python

import maya.api.OpenMaya as om
from maya import cmds

obj_name = "pCube1"
    
def get_connected_verts(obj_name, vert_index):
    vit = om.MItMeshVertex(get_shape(obj_name))
    vit.setIndex(vert_index)
    res = vit.getConnectedVertices()
    return res
    
vertices = get_connected_verts(obj_name, 431)


vertex_names = ["{}.vtx[{}]".format("pCube1", index) for index in vertices]
cmds.select(vertex_names, replace=True)

# Or:
select_vertices(obj_name, vertices)

def select_vertices(obj_name:str, vert_list:om.MIntArray) :
    mfn_components = om.MFnSingleIndexedComponent(get_MObject(obj_name))
    mfn_object = mfn_components.create(om.MFn.kMeshVertComponent)    
    mfn_components.addElements(vert_list)

    selection_list = om.MSelectionList()
    tuple = (get_MDagPath(obj_name), mfn_object)
    selection_list.add(tuple)
    om.MGlobal.setActiveSelectionList(selection_list)


def get_MDagPath(obj):
    if isinstance(obj, om.MDagPath):
        return obj

    if not isinstance(obj, om.MObject):
        obj = get_MObject(obj)

    assert obj.hasFn(om.MFn.kDagNode), ("This MObject is not a valid dag node, current type: "+obj.apiTypeStr())

    return om.MFnDagNode(obj).getPath()
        
        
def get_MObject(node_name):
    if isinstance(node_name, om.MObject):
        return node_name

    if isinstance(node_name, om.MDagPath):
        return node_name.node()

    slist = om.MSelectionList()
    try:
        slist.add(node_name)
    except RuntimeError:
        assert False, 'The node: "'+node_name+'" could not be found.'

    matches = slist.length()
    assert (matches == 1), 'Multiple nodes found for the same name: '+node_name

    obj = slist.getDependNode(0)
    return obj
    
        
def get_shape(node_name):
    if isinstance(node_name, om.MDagPath):
        dag_path = node_name
        dag_path.extendToShape()
        return dag_path.node()

    if isinstance(node_name, om.MObject):
        node = node_name
    elif isinstance(node_name, str):
        node = get_MObject(node_name)
    else:
        assert False, "unexpected type"

    # Find a shape node directly underneath the node.
    dag_path = om.MDagPath()
    dag_path = get_MDagPath(node)
    dag_path.extendToShape()
    return dag_path.node()

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