Applying per-vertex colors to new Bmesh

Question

I'm having trouble applying vertex colors through Python to a mesh. The mesh is imported from a file which has vertex info, face info (vertex indices), and a list of colors that corresponds to each vertex.

Creating the Bmesh mesh is fine:

bm = bmesh.new()
[bm.verts.new(v) for v in verts]
bm.verts.ensure_lookup_table()
[bm.faces.new([bm.verts[f[0]], bm.verts[f[1]], bm.verts[f[2]]]) for f in faces]
bm.faces.ensure_lookup_table()

However, I can't seem to find a way to apply colors to each vertex. Doing

color_layer = bm.loops.layers.color.new("color")
...    
bm.faces[i].loops['color'].vert

just yields a Bmesh vertex with an index of -1...

Is there anyway to get back the correct vertex indices in this way?

Answer 1

Loop over face loops.

import bpy
import bmesh
from random import uniform
context = bpy.context
mesh = context.object.data
bm = bmesh.new()
bm.from_mesh(mesh)

color_layer = bm.loops.layers.color.new("color")
# make a random color dict for each vert
# vert_color = random_color_table[vert]

def random_color(alpha=1):
    return [uniform(0, 1) for c in "rgb"] + [alpha]
random_color_table = {v : random_color()
                      for v in bm.verts}
for face in bm.faces:
    for loop in face.loops:
        loop[color_layer] = random_color_table[loop.vert]
bm.to_mesh(mesh)  

Should your table be indexed by vert index use something like

color_table[loop.vert.index]

If you notice that you are getting -1 for index value run

bm.verts.ensure_lookup_table()

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