CollideSoftBodyVerticesVsTriangles.h

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// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2024 Jorrit Rouwe
// SPDX-License-Identifier: MIT
 
#pragma once
 
#include <Jolt/Physics/Collision/CollideSoftBodyVertexIterator.h>
#include <Jolt/Geometry/ClosestPoint.h>
 
JPH_NAMESPACE_BEGIN

class JPH_EXPORT CollideSoftBodyVerticesVsTriangles
{
public:
                        CollideSoftBodyVerticesVsTriangles(Mat44Arg inCenterOfMassTransform, Vec3Arg inScale) :
        mTransform(inCenterOfMassTransform),
        mInvTransform(mTransform.InversedRotationTranslation()),
        mScale(inScale),
        mNormalSign(ScaleHelpers::IsInsideOut(inScale)? -1.0f : 1.0f)
    {
    }
 
    JPH_INLINE void     StartVertex(const CollideSoftBodyVertexIterator &inVertex)
    {
        mLocalPosition = mInvTransform * inVertex.GetPosition();
        mClosestDistanceSq = FLT_MAX;
    }
 
    JPH_INLINE void     ProcessTriangle(Vec3Arg inV0, Vec3Arg inV1, Vec3Arg inV2)
    {
        // Apply the scale to the triangle
        Vec3 v0 = mScale * inV0;
        Vec3 v1 = mScale * inV1;
        Vec3 v2 = mScale * inV2;
 
        // Get the closest point from the vertex to the triangle
        uint32 set;
        Vec3 closest_point = ClosestPoint::GetClosestPointOnTriangle(v0 - mLocalPosition, v1 - mLocalPosition, v2 - mLocalPosition, set);
        float dist_sq = closest_point.LengthSq();
        if (dist_sq < mClosestDistanceSq)
        {
            mV0 = v0;
            mV1 = v1;
            mV2 = v2;
            mClosestPoint = closest_point;
            mClosestDistanceSq = dist_sq;
            mSet = set;
        }
    }
 
    JPH_INLINE void     FinishVertex(const CollideSoftBodyVertexIterator &ioVertex, int inCollidingShapeIndex) const
    {
        if (mClosestDistanceSq < FLT_MAX)
        {
            // Convert triangle to world space
            Vec3 v0 = mTransform * mV0;
            Vec3 v1 = mTransform * mV1;
            Vec3 v2 = mTransform * mV2;
            Vec3 triangle_normal = mNormalSign * (v1 - v0).Cross(v2 - v0).NormalizedOr(Vec3::sAxisY());
 
            if (mSet == 0b111)
            {
                // Closest is interior to the triangle, use plane as collision plane but don't allow more than sTriangleThickness penetration
                // because otherwise a triangle half a level a way will have a huge penetration if it is back facing
                float penetration = triangle_normal.Dot(v0 - ioVertex.GetPosition());
                if (penetration < sTriangleThickness && ioVertex.UpdatePenetration(penetration))
                    ioVertex.SetCollision(Plane::sFromPointAndNormal(v0, triangle_normal), inCollidingShapeIndex);
            }
            else
            {
                // Closest point is on an edge or vertex, use closest point as collision plane
                Vec3 closest_point = mTransform * (mLocalPosition + mClosestPoint);
                Vec3 normal = ioVertex.GetPosition() - closest_point;
                if (normal.Dot(triangle_normal) > 0.0f) // Ignore back facing edges
                {
                    float normal_length = normal.Length();
                    float penetration = -normal_length;
                    if (ioVertex.UpdatePenetration(penetration))
                        ioVertex.SetCollision(Plane::sFromPointAndNormal(closest_point, normal_length > 0.0f? normal / normal_length : triangle_normal), inCollidingShapeIndex);
                }
            }
        }
    }

    static inline float sTriangleThickness = 0.1f;
 
    Mat44               mTransform;
    Mat44               mInvTransform;
    Vec3                mScale;
    Vec3                mLocalPosition;
    Vec3                mV0, mV1, mV2;
    Vec3                mClosestPoint;
    float               mNormalSign;
    float               mClosestDistanceSq;
    uint32              mSet;
};
 
JPH_NAMESPACE_END