Release v0.5.0

[sebcrozet]

v0.5.0 (16 August 2026)

Breaking changes

• ⚠ NexusState::insert_rigid_body/insert_rigid_body_in take an extra RbdCoupling argument.
  Pass RbdCoupling::None for a rigid-body-only scene.
• ⚠ Default solver parameters changed: contact_damping_ratio 5.0 → 10.0,
  normalized_allowed_linear_error 0.001 → 0.005, normalized_max_corrective_velocity
10.0 → 3.0, normalized_prediction_distance 0.002 → 0.02.
• ⚠ The viewer's BackendType::Rapier (CPU rapier reference backend) was removed. The remaining
  backends all run the nexus pipeline: Gpu, Cpu, Cuda, Metal.
• ⚠ Examples are prefixed by the subsystem they exercise (boxes3 → rbd_boxes3). The
  bench_joints3, bench_multibody_pendulum3 and bench_urdf3 benchmarks were removed.
• ⚠ Python: the PyPI distribution is now dimforge-nexus3d (the import name stays nexus3d).
• Built against rapier 0.35 and parry 0.30 (was rapier 0.34/parry 0.29).

Added

• nexus_mpm: a GPU Material Point Method solver, in 2D and 3D, behind the mpm feature.
  Particles are added and removed by chunk (NexusState::add_particles, extend_chunk,
  remove_chunk), on a sparse sorted grid with substepping and a CFL timestep bound.
• MPM constitutive models: linear and Neo-Hookean elasticity, Drucker-Prager sand (with cohesion),
  a weakly-compressible fluid, and the Stomakhin snow model, all built through ParticleModel.
• RbdCoupling::MpmOneWay: colliders act as moving boundaries for the particles, with per-body
  stick/slip/separate/non-reflecting conditions and optional CPIC for thin obstacles.
• RbdCoupling::MpmTwoWay hands a body over to MPM entirely: the rigid-body pipeline treats it as
  static while MPM integrates it from the particle impulses. At most 16 coupled bodies (CPIC limit).
• Multibody self-contacts: two links of the same multibody now collide, unless the multibody
  disables self-contacts.
• Restitution on multibody contacts, applied as an end-of-step pass seeded from the approach
  velocity measured at the start of the step.
• Per-link external forces/torques and gravity scale on multibody links
  (GpuMultibodySet::set_link_external_wrench), and DOF couplings between two joint axes.
• Multibody motors can be read back and retargeted at runtime (GpuMultibodySet::set_motor,
  set_motors, motor), plus set_num_internal_pgs_iterations and set_implicit_coriolis.
• RbdSimParams::static_contact_natural_frequency/static_contact_damping_ratio: contacts
  touching a fixed body get their own, stiffer by default, softness coefficients.
• RbdSimParams::normalized_max_linear_velocity (default 400.0 m/s) caps the linear velocity
  after each substep so speculative contacts stay reliable. Set to f32::MAX to disable.
• A brute-force O(n²) broad-phase, used instead of the LBVH for environments with at most
  64 colliders.
• NexusState::rbd_world_mut_untracked: mutate a rapier world after finalize without marking
  the GPU state dirty.
• Viewer: snap_rgb frame capture, configurable resolution, a headless mode, a vsync toggle,
  pipelined capture (render_async/render_flush) and kiss3d's GPU path tracer
  (raytrace_frame), all exposed to Python (PRs Add NexusViewer.render() to export frames off-screen #7, Add ability to generate python raytracing renderering #8 and Python: headless viewer, vsync control, pipelined frame capture #11 by @haixuanTao).
• Python bindings for MPM (set_mpm_params, add_particles, ParticleModel, …).
• A web-compat feature on the shader crates, enabled automatically when targeting wasm32.

Modified

• The contact solver follows rapier's TGS-soft relax pass: the unbiased normal rhs is refreshed
  from the post-integration poses, instead of stripping CFM and bias from the constraints in place.
• NexusState::set_rbd_gravity applies to free rigid-bodies and multibody links alike, and works
  in 2D (where the third component is ignored). It used to be 3D- and multibody-only.
• Extensive, mostly result-identical pipeline optimizations: frame-to-frame coloring, contacts
  bucket-sorted by color, fused colored sweeps, a shared-memory multibody PGS sweep, an SoA link
  workspace, LBVH subtree pruning, and skipping the pipelines that are provably inert.

Fixed

• RbdState::from_rapier zero-filled the velocity buffer, dropping every body's initial linear
  and angular velocity (PR fix: upload initial body velocities in the from_rapier bulk path #10 by @haixuanTao).
• Multibody joint limits no longer emit a constraint row while the joint sits strictly inside its
  bounds, where it can never apply an impulse (PR perf(rbd): skip inactive joint-limit constraint rows #14 by @haixuanTao).
• Contact manifold reduction now matches rapier's, including its degenerate-selection guards.
• The fused multibody solver kernels no longer place barriers under non-uniform control flow,
  which WebGPU rejects; the loop bound is now a uniform holding the max over all multibodies.
• Out-of-bounds writes to the polygonal-feature pair buffer, and constraint counting over the
  padded capacity instead of the real contact count.
• The LBVH pair traversal used a while loop, which naga might miscompile on macos.