Blender Onion Skinning (WIP)

onion_skin.py

import bpy
import gpu
from gpu_extras.batch import batch_for_shader
from collections import defaultdict

from time import time
from math import sin

shader = gpu.shader.from_builtin('3D_UNIFORM_COLOR')

mesh_cache = defaultdict(lambda: defaultdict(lambda: ([],[])))

def update_mesh_cache(scene):
    current_frame = scene.frame_current
    deps_graph = bpy.context.evaluated_depsgraph_get()
    
    for obj in bpy.context.selected_objects:
        evaluated_obj = obj.evaluated_get(deps_graph)
        
        obj_data = evaluated_obj.to_mesh()
        
        vertices = [
            (v.co.x, v.co.y, v.co.z)
            for v in obj_data.vertices
        ]
        indices=[
            (e.vertices[0], e.vertices[1])
            for e in obj_data.edges
        ]
        
        mesh_cache[current_frame][obj.name_full] = (vertices, indices)
        

def draw():
    shader.bind()
    shader.uniform_float("color", (1, 0, 0, 1))
    
    for per_frame_info in mesh_cache.values():
        for vertices, indices in per_frame_info.values():
        
            batch = batch_for_shader(
                shader, 
                'LINES', 
                {
                    "pos": vertices
                },
                indices=indices
            )
            batch.draw(shader)


bpy.types.SpaceView3D.draw_handler_add(draw, (), 'WINDOW', 'POST_VIEW')
bpy.app.handlers.frame_change_post.append(update_mesh_cache)