PBDShapeConstraintsBase.h

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// Copyright Epic Games, Inc. All Rights Reserved.
#pragma once
 
#include "Chaos/Core.h"
#include "Chaos/PBDSoftsEvolutionFwd.h"
#include "Chaos/Array.h"
#include "Chaos/PBDParticles.h"
#include "Chaos/PBDSoftsSolverParticles.h"
 
#include <functional>
 
namespace Chaos::Softs
{
 
class FPBDShapeConstraintsBase
{
public:
    FPBDShapeConstraintsBase(
        int32 InParticleOffset,
        int32 InParticleCount,
        const TArray<FSolverVec3>& StartPositions,
        const TArray<FSolverVec3>& InTargetPositions,
        const FSolverReal InStiffness
    )
        : TargetPositions(InTargetPositions)
        , ParticleOffset(InParticleOffset)
        , Stiffness(InStiffness)
    {
        const int32 NumConstraints = InParticleCount;
        Dists.SetNumUninitialized(InParticleCount);
        for (int32 Index = 0; Index < InParticleCount; ++Index)
        {
            const int32 ParticleIndex = ParticleOffset + Index;
            const FSolverVec3& P1 = StartPositions[ParticleIndex];
            const FSolverVec3& P2 = TargetPositions[ParticleIndex];
            Dists[Index] = (P1 - P2).Size();
        }
    }
    virtual ~FPBDShapeConstraintsBase() {}
 
    FSolverVec3 GetDelta(const FSolverParticles& InParticles, const int32 Index) const
    {
        checkSlow(Index >= ParticleOffset && Index < ParticleOffset + Dists.Num())
        if (InParticles.InvM(Index) == (FSolverReal)0.)
        {
            return FSolverVec3(0.);
        }
        const FSolverVec3& P1 = InParticles.P(Index);
        const FSolverVec3& P2 = TargetPositions[Index];
        const FSolverVec3 Difference = P1 - P2;
        const FSolverReal Distance = Difference.Size();
        const FSolverVec3 Direction = Difference / Distance;
        const FSolverVec3 Delta = (Distance - Dists[Index - ParticleOffset]) * Direction;
        return Stiffness * Delta / InParticles.InvM(Index);
    }
 
protected:
    const TArray<FSolverVec3>& TargetPositions;
    const int32 ParticleOffset;
 
private:
    TArray<FSolverReal> Dists;
    FSolverReal Stiffness;
};
 
}  // End namespace Chaos::Softs