| """Writes one convex hull collider per object: collision/<id>/<id>_collision.glb, plain glTF, no compression. |
| |
| Usage: hulls.py <jobs.json> <raw_folder> <collision_folder> [--max-points 64] |
| |
| The hull is taken over every mesh of the raw GLB in world space, then cut down to at most --max-points vertices by |
| farthest-point picking and hulled again, so PhysX, Unity (255 vertex cap), Rapier and Jolt take it as one convex |
| collider. The node carries extras.collision = {"shape": "convex_mesh", "points": n}. Prints one JSON line per object. |
| Run with python -I; needs trimesh, scipy and numpy. |
| """ |
| import json |
| import sys |
| from pathlib import Path |
|
|
| import numpy as np |
| import trimesh |
|
|
| FLAT_THRESHOLD_METRES = 1e-4 |
| SLAB_METRES = 0.01 |
|
|
|
|
| def farthest_points(points, count): |
| if len(points) <= count: |
| return points |
| chosen = [int(np.argmax(np.linalg.norm(points - points.mean(axis=0), axis=1)))] |
| distances = np.linalg.norm(points - points[chosen[0]], axis=1) |
| while len(chosen) < count: |
| next_index = int(np.argmax(distances)) |
| chosen.append(next_index) |
| distances = np.minimum(distances, np.linalg.norm(points - points[next_index], axis=1)) |
| return points[chosen] |
|
|
|
|
| def hull_for(raw_path, max_points): |
| scene = trimesh.load(raw_path, force="scene") |
| meshes = scene.dump(concatenate=False) if isinstance(scene, trimesh.Scene) else [scene] |
| points = np.concatenate([mesh.vertices for mesh in meshes if len(mesh.vertices)]) |
| extents = points.max(axis=0) - points.min(axis=0) |
| thin_axis = int(np.argmin(extents)) |
| if extents[thin_axis] < FLAT_THRESHOLD_METRES: |
| |
| offset = np.zeros(3) |
| offset[thin_axis] = -SLAB_METRES |
| points = np.concatenate([points, points + offset]) |
| hull = trimesh.convex.convex_hull(points) |
| reduced = trimesh.convex.convex_hull(farthest_points(np.asarray(hull.vertices), max_points)) |
| return reduced |
|
|
|
|
| def main(): |
| sys.stdout.reconfigure(encoding="utf-8", errors="replace") |
| jobs_path, raw_folder, collision_folder = sys.argv[1], Path(sys.argv[2]), Path(sys.argv[3]) |
| max_points = int(sys.argv[sys.argv.index("--max-points") + 1]) if "--max-points" in sys.argv else 64 |
| for item in json.loads(Path(jobs_path).read_text(encoding="utf-8")): |
| output_path = collision_folder / item["id"] / f"{item['id']}_collision.glb" |
| try: |
| hull = hull_for(raw_folder / f"{item['id']}.glb", max_points) |
| output_path.parent.mkdir(parents=True, exist_ok=True) |
| scene = trimesh.Scene() |
| scene.add_geometry(hull, node_name=f"{item['id']}_collision", geom_name=f"{item['id']}_hull") |
| scene.metadata["extras"] = {"collision": {"shape": "convex_mesh", "points": int(len(hull.vertices))}} |
| scene.export(output_path) |
| record = {"id": item["id"], "ok": True, "bytes": output_path.stat().st_size, "points": int(len(hull.vertices)), "volume_m3": float(hull.volume)} |
| except Exception as error: |
| record = {"id": item["id"], "ok": False, "reason": f"{type(error).__name__}: {str(error)[:300]}"} |
| print(json.dumps(record), flush=True) |
|
|
|
|
| if __name__ == "__main__": |
| main() |
|
|
