Module avian3d::dynamics

Rigid body dynamics, handling the motion and physical interactions of non-deformable objects.

A RigidBody is the core component of a physics simulation. It describes a rigid, non-deformable physics object that can be either dynamic, kinematic, or static.

Rigid body dynamics includes:

• Motion of rigid bodies based on their LinearVelocity and AngularVelocity.
• Acceleration caused by external forces and Gravity.
• Collision response, preventing objects from overlapping each other, considering properties such as Friction and Restitution.
• Joints connecting rigid bodies to each other.
• Everything else related to the physical behavior and properties of rigid bodies.

Rigid body dynamics does not include:

• Simulation of fluids (liquids and gasses)
• Elasticity (soft bodies)
• Plasticity (permanent deformation)

Plugins

Plugin	Description
IntegratorPlugin	Handles motion caused by velocity, and applies external forces and gravity.
SolverPlugin	Solves constraints (contacts and joints).
CcdPlugin	Performs sweep-based Continuous Collision Detection for bodies with the SweptCcd component to prevent tunneling.
SleepingPlugin	Manages sleeping and waking for bodies, automatically deactivating them to save computational resources.

Accuracy

The engine uses iterative algorithms to approximate the simulation. Thus, results may not be perfectly accurate:

• Constraints (contacts and joints) are not perfectly rigid.
  • Objects can overlap, especially in extreme stacking scenarios.
  • Contacts can be slightly bouncy even when the Restitution is zero.
  • Joint chains can stretch and in extreme cases have jittery behavior.
  • High mass ratios, such as when a very heavy object rests on top of a lighter one, can be difficult for the engine to deal with.
• Friction and Restitution may not be perfectly accurate.
• Objects moving at high speeds can pass through thin and small geometry due to discrete time steps, a phenomenon known as tunneling. This can be mitigated with Continuous Collision Detection.

These caveats are very common for physics engines intended for real-time applications, not something specific to this engine. Approximations are required for several reasons:

• Performance.
  • Exact results are simply not possible, especially at the frame rates expected from games and other real-time applications.
• Some differential equations do not have known exact solutions.
  • Semi-implicit Euler integration is used to approximate them.
• Some constraints cannot be solved uniquely.
  • An iterative Gauss-Seidel solver is used to solve them approximately.

In practice, the results should be accurate enough for most real-time applications. Perfect accuracy is very rarely necessary, if ever, and most of the more visible issues can typically be worked around.

Modules

• ccd
  Contains components and functionality for Continuous Collision Detection.
• integrator
  Applies forces and velocities to bodies in order to move them according to the equations of motion using numerical integration.
• prelude
  Re-exports common types related to the rigid body dynamics functionality.
• rigid_body
  Common components and bundles for rigid bodies.
• sleeping
  Manages sleeping and waking for bodies, automatically deactivating them to save computational resources.
• solver
  Manages and solves contacts, joints, and other constraints.