Blender: Visualize vertex weight distribution

visualize_vertex_weight_distribution.py

# by Razgriz
# Use sum of weights (raised to a defined power) to visualize how many weights affect vertices
#   Darker -> less groups affecting vert
#   Lighter -> many groups affecting vert 
# 
# May be useful for determining where to reduce topological density with minimal deformation impact
#
# If any verts are unweighted, they'll be set to magenta ((1,0,1) / #FFOOFF) and selected in edit mode
#
# To Use:
# Open Scripting Workspace (tab at top)
# Create a new script
# Paste script content in text editor
# Select Object in object mode
# Run script
#
# Note: Will create or overwrite the vertex color layer named 'WeightDistribution'
#       Will switch mode to Vertex Paint to visualize 

weight_power = 6

import bpy

object = bpy.context.active_object.data
verts = object.vertices
color_map_collection = object.vertex_colors

unweighted_verts = []

# Create layer if it doesn't exist already
layer_name = 'WeightDistribution'
has_layer  = False
for collection in color_map_collection:
    if collection.name == layer_name:
        has_layer = True

if not has_layer:
    color_map_collection.new(name=layer_name)

color_map = color_map_collection[layer_name]

# Loop across polygons and verts
i = 0
for poly in object.polygons:
    for idx in poly.loop_indices:
        loop = object.loops[idx]
        v = loop.vertex_index
        val = 0
        groups = verts[v].groups
        
        if len(groups) > 0:
            for g in groups:
                val += pow(g.weight, weight_power)
            val = max(min(1 - val, 1), 0)
            final_color = (val, val, val, 1.0)
        else:
            final_color = (1, 0, 1, 1) # if no groups, set to magenta
            unweighted_verts.append(verts[v].index)
            
        t = 0
        color_map.data[i].color = final_color
        i += 1

if len(unweighted_verts) > 0:
    bpy.ops.object.mode_set(mode = 'EDIT') 
    bpy.ops.mesh.select_mode(type="VERT")
    bpy.ops.mesh.select_all(action = 'DESELECT')
    bpy.ops.object.mode_set(mode = 'OBJECT')
    for vid in unweighted_verts:
        object.vertices[vid].select = True
    bpy.ops.object.mode_set(mode = 'EDIT')
    for area in bpy.context.screen.areas: # zoom to selected
        if area.type == 'VIEW_3D':
            ctx = bpy.context.copy()
            ctx['area'] = area
            ctx['region'] = area.regions[-1]
            bpy.ops.view3d.view_selected(ctx)            # points view

    
else:
    object.vertex_colors.active = object.vertex_colors[layer_name]
    bpy.ops.object.mode_set(mode='VERTEX_PAINT')