Python: assign custom tag to vertices

Question

Is it possible to associate a custom tag with each vertex?

I would like to be able to number them...

I have an export script that dumps 6000 vertices to file, I then run a simulation that generates an array for each vertex.

But I would like to be able to give each vertex a unique ID as it is written to file, so that I can select a dozen vertices in blender, and export a list of IDs (and then process the array for each)

How can I do this?

LINK: http://blenderartists.org/forum/showthread.php?318031-Property-for-each-individual-face

Answer 1

It is possible to tag vertices with the bmesh module:

bm = bmesh.from_edit_mesh(obj.data)
#or
bm = bmesh.new()
bm.from_mesh(obj.data)

#create custom data layers
my_id = bm.verts.layers.int.new('id')

#get the custom data layer by its name
my_id = bm.verts.layers.int['id']

#access
bm.verts[0][my_id] = 42

#apply the changes
bmesh.update_edit_mesh(obj.data)
#or
bm.to_mesh(obj.data)

Answer 2

You can count vertices on export and use that instead of the vertex indices:

import bpy

c = 0

for ob in bpy.context.scene.objects:
    if ob.type == 'MESH':
        me = ob.data
        print("Mesh %s (%s):" % (me.name, ob.name))

        for i, v in enumerate(me.vertices, c):
            print("  Vert %i - %i" % (i, v.index))
        c += len(me.vertices)
        print()

And here all selected verts of all mesh objects in scene:

# Simple

def count_selected_verts(file):
    c = 0

    for ob in bpy.context.scene.objects:
        if ob.type == 'MESH':
            if ob.mode == 'EDIT':
                ob.update_from_editmode()
            me = ob.data
            file.write("Mesh %s (%s):" % (me.name, ob.name))

            for v in me.vertices:
                if v.select:
                    file.write("%5i - Vert %i\n" % (c, v.index))
                    c += 1
    file.close()

# Pythonic - generator and list comprehension with a hacky filter

# This is infinite, don't cast to sequence!
def countup():
    i = 0
    while True:
        yield i
        i += 1

def ob_update(ob):
    # Prints all mesh objects at the top of the file :/
    #file.write("Mesh %s (%s):" % (ob.data.name, ob.name))
    if ob.mode == 'EDIT':
        ob.update_from_editmode()
    return True


def count_selected_verts_gen(file):
    c = countup()
    for ob in bpy.context.scene.objects:
        if ob.type == 'MESH' and ob_update(ob):
            file.write("Mesh %s (%s):" % (me.name, ob.name))
            file.write("\n".join("%5i - Vert %i" % (c.__next__(), v.index)
                for v in ob.data.vertices if v.select)
            )
    file.close()

I compared the performance: 22.0 vs. 9.4 secs (pythonic is win!).