Jolt and Rapier

comparison.md

Comparing Rapier and Jolt

General Properties

Both Jolt and Rapier:

• Support single and double precision simulation

Only Jolt:

• Supports soft-body physics
• Supports multiple object layers
• Supports multiple broad phase layers
  • This is big for us as Rapier's broad phase has been the root of some of our performance issues

Only Rapier:

• Has the user hold storage for bodies, colliders, and joints, which makes preventing aliasing easy but creates some interesting APIs

Body

Jolt Body Rapier RigidBody

Both Jolt and Rapier have Bodies with:

• A transform
• Linear and angular velocity
• An API to apply forces and torques, either at CoM or a point
• Per-body User data (8 bytes in Jolt, 16 bytes in Rapier)
• Per-body CCD configuration

Only Jolt has Bodies with:

• One Shape
• Restitution (stored on Collider in Rapier)
• Friction (stored on Collider in Rapier)

Only Rapier has Bodies with:

• One or more Colliders

Collider

Rapier Collider/ColliderBuilder

In between Bodies and Shapes, Rapier has the concept of a Collider, which contains a shape and defines some rigid body and simulation properties.

Rapier Colliders have:

• One Shape
• Collision group and mask (stored on Body in Jolt, conceptually)
  • Rapier has no broad phase or object layer filters, so this is the primary filtering mechanism
• Density (stored on Shape in Jolt)
• Friction (stored on Body in Jolt)
• Restitution (stored on Body in Jolt)
• User data (16 bytes)

Shape

Rapier Shape/SharedShape Jolt Shape

Both Jolt and Rapier have Shapes with:

• Several primitive types (boxes, spheres, convex hulls)
• Static compound shapes (Rapier SharedShape::compound and Jolt StaticCompoundShape)
  • Note that Rapier has limitations as to what shapes can be part of compound shapes
• Refcounted shape handles (Ref<Shape> in Jolt, SharedShape in Rapier)

Only Jolt Shapes have:

• User data (8 bytes)
• Density (stored on Collider in Rapier)
• Built-in convex decomposition (SharedShape::convex_decomposition)
• Mutable compound shapes (MutableCompoundShape)
  • In Rapier, you'd use multiple colliders and move the colliders instead. Colliders can additionally have separate collision groups and materials.

Joint

Both Jolt and Rapier have Joint objects with:

• References to bodies they affect
• Several built-in and configurable joint types
• Multi-body joints for ragdolls