CCDModification.h

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// Copyright Epic Games, Inc. All Rights Reserved.
#pragma once
 
#include "Chaos/Core.h"
#include "ParticleHandleFwd.h"
 
namespace Chaos
{
    class FCCDModifier;
    class FCCDModifierAccessor;
    class FCCDModifierParticleIterator;
    class FCCDModifierParticleRange;
    class FPBDCollisionConstraint;
 
    /*
     * Allows the user to modify the results of CCD collision detection prior to the CCD rewind being
     * applied. This is in addition to the midphase modification phase which happens before collision
     * detection has been run, and the contact modifier phase which happens after we have rewound
     * 
     * The CCD "contact" details reported here do not necessarily represent the contact details
     * that will be used in the contact solving phase. The CCD data provides raw first-touch data from
     * a swept collision detection test, but we will be rebuilding a full contact manifold at the 
     * post-CCD position. The CCD normal and position here are not used again. For example, it is not
     * a good idea to use the CCD data to categorize collisions as wall or floor contacts. If you need
     * to know the actual contact positions and normals that will be used in the contact reoslution
     * phase, then see FCollisionContactModifier.
     * 
     * @see FMidPhaseModifier, FContactPairModifier
     */
    class FCCDModifier
    {
    public:
        FCCDModifier()
            : Constraint(nullptr)
        {}
 
        bool IsValid() const
        {
            return Constraint != nullptr;
        }
 
        //
        // Accessor functions
        //
 
        // Whether the two particle actually hit each other in the sweep
        CHAOS_API bool IsSweepHit() const;
 
        // Get the time of impact. This is as a fraction of total movement and will be in the range [0,1] if a hit was found
        CHAOS_API FReal GetSweepHitTOI() const;
 
        // Get the sweep impact position for the specified body
        // NOTE: See class comments.
        CHAOS_API FVec3 GetWorldSweepHitLocation(const int32 ParticleIndex) const;
 
        // Get the sweep impact normal
        // NOTE: See class comments.
        CHAOS_API FVec3 GetWorldSweepHitNormal() const;
 
        CHAOS_API const FGeometryParticleHandle* GetParticle(const int32 ParticleIndex) const;
        CHAOS_API const FGeometryParticleHandle* GetOtherParticle(const FGeometryParticleHandle* InParticle) const;
 
        //
        // Modifying functions
        //
 
        // Re-enable this contact (if it was previously disabled)
        CHAOS_API void Enable();
 
        // Disable this contact
        CHAOS_API void Disable();
 
        // Convert this contact to a probe
        CHAOS_API void ConvertToProbe();
 
    private:
        FCCDModifier(
            FCCDModifierAccessor* InAccessor,
            FPBDCollisionConstraint* InConstraint)
            : Accessor(InAccessor)
            , Constraint(InConstraint)
        {}
 
        void Reset()
        {
            Accessor = nullptr;
            Constraint = nullptr;
        }
 
        FCCDModifierAccessor* Accessor;
        FPBDCollisionConstraint* Constraint;
 
        friend class FCCDModifierParticleIterator;
    };
 
    /*
     * Class for iterating over ccd results involving a specific particle
     */
    class FCCDModifierParticleIterator
    {
    public:
        FCCDModifier& operator*()
        {
            return PairModifier;
        }
 
        FCCDModifier* operator->()
        {
            return &PairModifier;
        }
 
        FCCDModifierParticleIterator& operator++()
        {
            return MoveToNext();
        }
 
        explicit operator bool() const
        {
            return PairModifier.IsValid();
        }
 
        friend bool operator==(const FCCDModifierParticleIterator& L, const FCCDModifierParticleIterator& R)
        {
            return (L.Range == R.Range) && (L.ConstraintIndex == R.ConstraintIndex);
        }
 
        friend bool operator!=(const FCCDModifierParticleIterator& L, const FCCDModifierParticleIterator& R)
        {
            return !(L == R);
        }
 
    private:
        FCCDModifierParticleIterator(FCCDModifierParticleRange* InRange)
            : Range(InRange)
            , ConstraintIndex(INDEX_NONE)
        { 
        }
 
        CHAOS_API FCCDModifierParticleIterator& MoveToBegin();
        CHAOS_API FCCDModifierParticleIterator& MoveToEnd();
        CHAOS_API FCCDModifierParticleIterator& MoveToNext();
 
        FCCDModifierParticleRange* Range;
        int32 ConstraintIndex;
        FCCDModifier PairModifier;
 
        friend class FCCDModifierParticleRange;
    };
 
    /*
     * Represents all the swept constraints on a particle to allow for iteration.
     */
    class FCCDModifierParticleRange
    {
    public:
        CHAOS_API FCCDModifierParticleRange(
            FCCDModifierAccessor* InAccessor, 
            FGeometryParticleHandle* InParticle);
 
        CHAOS_API FCCDModifierParticleIterator begin();
        CHAOS_API FCCDModifierParticleIterator end();
 
    private:
        FCCDModifierAccessor* GetAccessor() const { return Accessor; }
        FGeometryParticleHandle* GetParticle() const { return Particle; }
        int32 GetNumConstraints() const { return Constraints.Num(); }
        FPBDCollisionConstraint* GetConstraint(const int32 Index) const { return Constraints[Index]; }
        CHAOS_API void CollectConstraints();
 
        FCCDModifierAccessor* Accessor;
        FGeometryParticleHandle* Particle;
        TArray<FPBDCollisionConstraint*> Constraints;
 
        friend class FCCDModifierParticleIterator;
    };
 
    /*
     * Provides access to CCD modifiers
     */
    class FCCDModifierAccessor
    {
    public:
        CHAOS_API FCCDModifierAccessor(const FReal InDt);
 
        // Get an object which allows for range iteration over the CCD modifiers for a particle
        CHAOS_API FCCDModifierParticleRange GetModifiers(FGeometryParticleHandle* Particle);
 
        FReal GetDt() const
        {
            return Dt;
        }
 
    private:
        FReal Dt;
    };
}