Newton Alignment¶

NovaPhy is being progressively reshaped to align with the Newton physics engine by Disney Research / Google DeepMind / NVIDIA — a GPU-accelerated, batched, differentiable physics engine built on NVIDIA Warp.

Motivation¶

Shared Model / State / Control / Contacts abstraction — One scene description, one state object, many pluggable solvers.
Unified SolverBase.step() contract — Out-of-place stepping makes checkpoint/restore, parallel rollout, and differentiable rollout straightforward.
Clear solver taxonomy — Users pick SolverFeatherstone, SolverSemiImplicit, SolverXPBD, SolverVBD without understanding legacy class hierarchies.
Batched multi-world data layout — Embodied-intelligence training needs thousands of worlds per GPU.

Current Status¶

Completed¶

Change	Details
`SolverSemiImplicit`	Renamed from `SolverSequentialImpulse`, absorbs legacy `FreeBodySolver`
`SolverFeatherstone`	Renamed from `MultiBodySolver`
`SolverBase` contract	Out-of-place `step(model, state_in, state_out, control, contacts, dt)`
`Contacts` aggregate	Unified `rigid` / `manifolds` / `particle` / `soft` channels
`JointSupportMatrix`	Declarative per-solver joint type support
`SolverNotifyFlags`	Bit-mask for model change notifications

New Public Types¶

Type	Header	Purpose
`Contacts`	`core/contacts.h`	Unified contact aggregate
`ParticleContact`	`core/contacts.h`	Particle-rigid contact (for PBF/MPM)
`SoftContact`	`core/contacts.h`	Soft-element contact (for VBD/IPC)
`SolverNotifyFlags`	`dynamics/solver_base.h`	Model change bit-mask
`JointSupportMatrix`	`dynamics/solver_base.h`	Per-solver joint support table

SolverBase Interface¶

class SolverBase {
public:
    // Legacy in-place step (unchanged)
    virtual void step(const Model&, SimState&, const Control&, float dt,
                      const Vec3f& gravity) = 0;

    // Newton-aligned out-of-place step
    virtual void step(const Model&, const SimState& in, SimState& out,
                      const Control*, Contacts*, float dt, const Vec3f& gravity);

    virtual void notify_model_changed(SolverNotifyFlags flags);
    virtual void update_contacts(Contacts& out, const SimState* state) const;
    virtual JointSupportMatrix joint_support() const;
};

Roadmap¶

Step	Scope	Risk	Status
Rename solvers	`SolverSequentialImpulse` -> `SolverSemiImplicit`, `MultiBodySolver` -> `SolverFeatherstone`	Breaking	Done
Delete `ArticulatedSolver`	Migrate to `featherstone::*` primitives	Breaking	Done
VBD/IPC as solvers	`VBDWorld` -> `SolverVBD`, `IPCWorld` -> `SolverIPC` headers	Medium	Done
Unify joint taxonomy	`DISTANCE` / `D6` / `CABLE`; merge `XPBDJoint` into `Joint`	Medium	Planned
Extend SolverXPBD	Articulations, torsional + rolling friction	Medium	Partial
Slim World	`std::vector<SolverBase*>` pipeline; promote `PBFSolver` to `SolverPBF`	Medium	Planned
Batched multi-world	`*_world` index arrays, per-world gravity, world-partitioned SAP	Large	Planned
DeviceArray abstraction	`DeviceArray<T>` / `DeviceContext`; SoA kernel rewrite	Large	Planned
SolverMPM, SolverLBM	MPM/LBM solvers + Akinci coupling pass	Large	Scaffolds exist
SolverMuJoCo	Soft-constraint CG/PGS + MJCF importer	Large	Planned
Differentiable rollout	Adjoint / Warp-Tape-style	Large	Planned

Using the New API¶

import novaphy

# Unified contact aggregate
contacts = novaphy.Contacts()
assert contacts.empty()

# Newton-style solver metadata
solver = novaphy.SolverSemiImplicit()
assert isinstance(solver, novaphy.SolverBase)
matrix = solver.joint_support()
solver.notify_model_changed(novaphy.SolverNotifyFlags.ModelProperties)
solver.update_contacts(contacts)