Bug Report: Attached objects ignore collisions with Normal Objects (FCL primitives)

[confucianism72]

Description

In mplib's PlanningWorld, objects attached to the robot (via update_attached_box or attach_object) correctly trigger collisions with Point Clouds, but are completely ignored when checking against Normal Objects (FCL primitives added via set_normal_object).

Steps to Reproduce

1. Create a PlanningWorld and add an articulated robot.
2. Add a primitive Box as an environment obstacle using set_normal_object.
3. Attach another Box to the robot's end-effector using update_attached_box.
4. Position the robot so that the attached box intersects with the environment obstacle.
5. Call check_for_env_collision(use_attach=True) or planning_world.collide_with_others().

Observed Behavior

The collision check returns False (no collision), even if the attached object is significantly larger than the obstacle.

However, if the same obstacle is added as a Point Cloud instead of a Normal Object, the collision is detected correctly with the trace: attached_tool collides with point_cloud.

Expected Behavior

Attached objects should be included in the collision check against Normal Objects when use_attach is enabled.

Minimal Code Example

import numpy as np
from mplib import Planner
from mplib.pymp.collision_detection import fcl

# ... Setup planner and world ...

# 1. Add environment obstacle
obs_geom = fcl.Box([0.1, 0.1, 0.1])
obs_obj = fcl.CollisionObject(obs_geom, [0.4, 0.0, 0.05], [1, 0, 0, 0])
planner.set_normal_object("obstacle", obs_obj)

# 2. Attach a monster box to the end-effector (2m large)
planner.update_attached_box([2.0, 2.0, 2.0], [0, 0, 0, 1, 0, 0, 0])

# 3. Check collision
# Actual: returns [], Expected: should detect collision with "obstacle"
results = planner.check_for_env_collision(use_attach=True)
print(f"Collision detected: {len(results) > 0}")

Environment

• OS: Linux
• Python version: 3.10
• mplib version: latest

Additional Context

It seems the collision matrix in PlanningWorld might be missing the Attached Body vs Normal Object interaction layer, while the Attached Body vs Point Cloud layer works as intended.

[confucianism72]

mplib version is 0.1.1

[confucianism72]

In PlanningWorldTpl<S>::collideWithOthers, the logic for use_attach_ is nested under use_point_cloud_. Moreover, it only checks collision against point_cloud_ and lacks a loop to check against normal_object_map_.

[confucianism72]

Oh I found this is solved in v0.2.1。 I am still using 0.1.1 because Maniskill strictly requires it.

[confucianism72]

well, upgrade MPlib to 0.2.1 fails the IK in Maniskill due to some unknown reason