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  3. FPBDCollisionSolverJacobi

FPBDCollisionSolverJacobi

A Jocobi solver for the contact manifold between two shapes.

API > API/Runtime > API/Runtime/Chaos

A Jocobi solver for the contact manifold between two shapes. This solves each manifold point independently and sums and dampens the net impulses before applying to the bodies.

Pros (vs Gauss Seidel):

  • If the contacts are symmetric, the impusles will be too. This fixed spurious rotations when a box with high restitution bounces exactly flat on the ground.
  • We can run the points in the manifold in parallel
  • Stacking is much more stable (but see below) Cons
  • We overestimate the impulse and must apply a damping factor to prevent energy gain. It is not clear how we select the value of this damping - it is empirically tuned.
  • The damping factor leads to spongey stacks/piles
   
Name FPBDCollisionSolverJacobi
Type class
Header File /Engine/Source/Runtime/Experimental/Chaos/Public/Chaos/Collision/PBDCollisionSolverJacobi.h
Include Path #include "Chaos/Collision/PBDCollisionSolverJacobi.h"

Syntax

class FPBDCollisionSolverJacobi

Constructors

Name Remarks Include Path Unreal Specifiers

FPBDCollisionSolverJacobi()

 NOTE: Does not initialize any properties. See MakeInitialized. Chaos/Collision/PBDCollisionSolverJacobi.h  

Structs

Name Remarks
FState  

Constants

Name Type Remarks Include Path
MaxConstrainedBodies const int32   Chaos/Collision/PBDCollisionSolverJacobi.h
MaxPointsPerConstraint const int32   Chaos/Collision/PBDCollisionSolverJacobi.h

Variables

Protected

Name Type Remarks Include Path Unreal Specifiers
State FState   Chaos/Collision/PBDCollisionSolverJacobi.h  

Functions

Public

Name Remarks Include Path Unreal Specifiers

int32 AddManifoldPoint()

   Chaos/Collision/PBDCollisionSolverJacobi.h  

void DisableShockPropagation()

 Disable mass scaling. Chaos/Collision/PBDCollisionSolverJacobi.h  

FSolverReal DynamicFriction()

   Chaos/Collision/PBDCollisionSolverJacobi.h  

void EnablePositionShockPropagation()

 Set up the mass scaling for shock propagation, using the position-phase mass scale. Chaos/Collision/PBDCollisionSolverJacobi.h  

void EnableVelocityShockPropagation()

 Set up the mass scaling for shock propagation, using the velocity-phase mass scale. Chaos/Collision/PBDCollisionSolverJacobi.h  

void FinalizeManifoldPoint ( const int32 ManifoldPointIndex
)

 Finish manifold point setup. NOTE: Can only be called after the InitManifoldPoint has been called Chaos/Collision/PBDCollisionSolverJacobi.h  

FSolverVec3 GetNetImpulse ( const int32 ManifoldPointIndex
) const

   Chaos/Collision/PBDCollisionSolverJacobi.h  

FSolverVec3 GetNetPushOut ( const int32 ManifoldPointIndex
) const

   Chaos/Collision/PBDCollisionSolverJacobi.h  

FSolverReal GetStaticFrictionRatio ( const int32 ManifoldPointIndex
) const

   Chaos/Collision/PBDCollisionSolverJacobi.h  

void InitManifoldPoint ( const int32 ManifoldPointIndex,
const FSolverVec3& InRelativeContactPosition0,
const FSolverVec3& InRelativeContactPosition1,
const FSolverVec3& InWorldContactNormal,
const FSolverVec3& InWorldContactTangentU,
const FSolverVec3& InWorldContactTangentV,
const FSolverReal InWorldContactDeltaNormal,
const FSolverReal InWorldContactDeltaTangentU,
const FSolverReal InWorldContactDeltaTangentV,
const FSolverReal InWorldContactVelocityTargetNormal
)

   Chaos/Collision/PBDCollisionSolverJacobi.h  

int32 NumManifoldPoints()

   Chaos/Collision/PBDCollisionSolverJacobi.h  

void Reset()

 Reset the state of the collision solver Chaos/Collision/PBDCollisionSolverJacobi.h  

void ResetManifold()

   Chaos/Collision/PBDCollisionSolverJacobi.h  

void SetFriction ( const FSolverReal InStaticFriction,
const FSolverReal InDynamicFriction,
const FSolverReal InVelocityFriction
)

   Chaos/Collision/PBDCollisionSolverJacobi.h  

void SetManifoldPoint ( const int32 ManifoldPointIndex,
const FSolverVec3& InRelativeContactPosition0,
const FSolverVec3& InRelativeContactPosition1,
const FSolverVec3& InWorldContactNormal,
const FSolverVec3& InWorldContactTangentU,
const FSolverVec3& InWorldContactTangentV,
const FSolverReal InWorldContactDeltaNormal,
const FSolverReal InWorldContactDeltaTangentU,
const FSolverReal InWorldContactDeltaTangentV,
const FSolverReal InWorldContactVelocityTargetNormal
)

 Set up a manifold point (also calls FinalizeManifoldPoint) Chaos/Collision/PBDCollisionSolverJacobi.h  

void SetSolverBodies ( FSolverBody& SolverBody0,
FSolverBody& SolverBody1
)

   Chaos/Collision/PBDCollisionSolverJacobi.h  

void SetStiffness ( const FSolverReal InStiffness
)

   Chaos/Collision/PBDCollisionSolverJacobi.h  

bool SolvePositionNoFriction ( const FSolverReal Dt,
const FSolverReal MaxPushOut
)

 Calculate and apply the position correction for this iteration. Chaos/Collision/PBDCollisionSolverJacobi.h  

bool SolvePositionWithFriction ( const FSolverReal Dt,
const FSolverReal MaxPushOut
)

   Chaos/Collision/PBDCollisionSolverJacobi.h  
Get the first (decorated) solver body The decorator add a possible mass scale. Chaos/Collision/PBDCollisionSolverJacobi.h  
  Chaos/Collision/PBDCollisionSolverJacobi.h  
Get the second (decorated) solver body The decorator add a possible mass scale. Chaos/Collision/PBDCollisionSolverJacobi.h  
  Chaos/Collision/PBDCollisionSolverJacobi.h  

bool SolveVelocity ( const FSolverReal Dt,
const bool bApplyDynamicFriction
)

 Calculate and apply the velocity correction for this iteration. Chaos/Collision/PBDCollisionSolverJacobi.h  

FSolverReal StaticFriction()

   Chaos/Collision/PBDCollisionSolverJacobi.h  

FSolverReal VelocityFriction()

   Chaos/Collision/PBDCollisionSolverJacobi.h  

Static

Name Remarks Include Path Unreal Specifiers

static FPBDCollisionSolverJacobi MakeInitialized()

 Create a solver that is initialized to safe defaults. Chaos/Collision/PBDCollisionSolverJacobi.h  

static FPBDCollisionSolverJacobi MakeUninitialized()

 Create a solver with no initialization. Chaos/Collision/PBDCollisionSolverJacobi.h  

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