PBDTetConstraintsBase.h

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// Copyright Epic Games, Inc. All Rights Reserved.
#pragma once
 
#include "Chaos/Array.h"
#include "Chaos/PBDSoftsEvolutionFwd.h"
#include "Chaos/PBDParticles.h"
#include "Chaos/DynamicParticles.h"
#include "Chaos/PBDParticles.h"
#include "Chaos/PBDSoftsSolverParticles.h"
 
namespace Chaos::Softs
{
 
class FPBDTetConstraintsBase
{
public:
    FPBDTetConstraintsBase(const FSolverParticles& InParticles, TArray<TVec4<int32>>&& InConstraints, const FSolverReal InStiffness = (FSolverReal)1.)
        : Constraints(InConstraints), Stiffness(InStiffness)
    {
        for (const TVec4<int32>& Constraint : Constraints)
        {
            const FSolverVec3& P1 = InParticles.GetX(Constraint[0]);
            const FSolverVec3& P2 = InParticles.GetX(Constraint[1]);
            const FSolverVec3& P3 = InParticles.GetX(Constraint[2]);
            const FSolverVec3& P4 = InParticles.GetX(Constraint[3]);
            Volumes.Add(FSolverVec3::DotProduct(FSolverVec3::CrossProduct(P2 - P1, P3 - P1), P4 - P1) / (FSolverReal)6.);
        }
    }
    virtual ~FPBDTetConstraintsBase() {}
 
    TVec4<FSolverVec3> GetGradients(const FSolverParticles& InParticles, const int32 i) const
    {
        TVec4<FSolverVec3> Grads;
        const TVec4<int32>& Constraint = Constraints[i];
        const FSolverVec3& P1 = InParticles.P(Constraint[0]);
        const FSolverVec3& P2 = InParticles.P(Constraint[1]);
        const FSolverVec3& P3 = InParticles.P(Constraint[2]);
        const FSolverVec3& P4 = InParticles.P(Constraint[3]);
        const FSolverVec3 P2P1 = P2 - P1;
        const FSolverVec3 P4P1 = P4 - P1;
        const FSolverVec3 P3P1 = P3 - P1;
        Grads[1] = FSolverVec3::CrossProduct(P3P1, P4P1) / (FSolverReal)6.;
        Grads[2] = FSolverVec3::CrossProduct(P4P1, P2P1) / (FSolverReal)6.;
        Grads[3] = FSolverVec3::CrossProduct(P2P1, P3P1) / (FSolverReal)6.;
        Grads[0] = -(Grads[1] + Grads[2] + Grads[3]);
        return Grads;
    }
 
    FSolverReal GetScalingFactor(const FSolverParticles& InParticles, const int32 i, const TVec4<FSolverVec3>& Grads) const
    {
        const TVec4<int32>& Constraint = Constraints[i];
        const int32 i1 = Constraint[0];
        const int32 i2 = Constraint[1];
        const int32 i3 = Constraint[2];
        const int32 i4 = Constraint[3];
        const FSolverVec3& P1 = InParticles.P(i1);
        const FSolverVec3& P2 = InParticles.P(i2);
        const FSolverVec3& P3 = InParticles.P(i3);
        const FSolverVec3& P4 = InParticles.P(i4);
        const FSolverReal Volume = FSolverVec3::DotProduct(FSolverVec3::CrossProduct(P2 - P1, P3 - P1), P4 - P1) / (FSolverReal)6.;
        const FSolverReal S = (Volume - Volumes[i]) / (
            InParticles.InvM(i1) * Grads[0].SizeSquared() +
            InParticles.InvM(i2) * Grads[1].SizeSquared() + 
            InParticles.InvM(i3) * Grads[2].SizeSquared() + 
            InParticles.InvM(i4) * Grads[3].SizeSquared());
        return Stiffness * S;
    }
 
protected:
    TArray<TVec4<int32>> Constraints;
 
private:
    TArray<FSolverReal> Volumes;
    FSolverReal Stiffness;
};
 
}  // End namespace Chaos::Softs