RigidElasticSim/comparisons/Bullet

Bullet Comparison

Bullet provides two ways of modeling contacts between complex geometries. Similar to our method, the first way uses the triangle mesh geometry directly (btGImpactMeshShape). The second way uses convex shapes (or compound convex shapes). Bullet additionally, provides a direct way of generating approximate convex decompositions of concave shapes through Volumetric Hierarchical Approximate Decomposition (V-HACD).

Triangle Mesh Collisions (btGImpactMeshShape)

We modified the ImportMJCFDemo example to automatically take an MJCF scene file as input, run the scene for 10 simulated seconds, and then terminate. We use GImpact for any input triangle meshes, and enforce only one substep for each time step (time step size fixed at 1e-2, 1e-3, or 1e-4 s for our experiments). To do this we implemented mesh volume computation and enabled automatic mass computation from density input (m=ρV), and we also enabled mesh scaling, dt, and mu setting from MJCF file which are not supported in the original demo.

See our repository on Github for more details: https://github.com/liminchen/bullet3

Scene MJCF files can be found in the MJCF directory (files with extension .xml).

Convex Shapes and V-HACD

We additionally compare against the convex decompositions of our meshes. We do this directly using PyBullet Python bindings. We directly load our JSON fixtures and use V-HACD to decompose concave meshes.

Prerequisites

PyBullet Python bindings can be installed using:

pip install pybullet

For videos, make sure ffmpeg is installed and in the path.

Running Simulation

To run the comparison run python benchmark.py.