b2_rope.h

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// MIT License

// Copyright (c) 2019 Erin Catto

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#ifndef B2_ROPE_H
#define B2_ROPE_H

#include "b2_api.h"
#include "b2_math.h"

class b2Draw;
struct b2RopeStretch;
struct b2RopeBend;

enum b2StretchingModel
{
        b2_pbdStretchingModel,
        b2_xpbdStretchingModel
};

enum b2BendingModel
{
        b2_springAngleBendingModel = 0,
        b2_pbdAngleBendingModel,
        b2_xpbdAngleBendingModel,
        b2_pbdDistanceBendingModel,
        b2_pbdHeightBendingModel,
        b2_pbdTriangleBendingModel
};

struct B2_API b2RopeTuning
{
        b2RopeTuning()
        {
                stretchingModel = b2_pbdStretchingModel;
                bendingModel = b2_pbdAngleBendingModel;
                damping = 0.0f;
                stretchStiffness = 1.0f;
                bendStiffness = 0.5f;
                bendHertz = 1.0f;
                bendDamping = 0.0f;
                isometric = false;
                fixedEffectiveMass = false;
                warmStart = false;
        }

        b2StretchingModel stretchingModel;
        b2BendingModel bendingModel;
        float damping;
        float stretchStiffness;
        float stretchHertz;
        float stretchDamping;
        float bendStiffness;
        float bendHertz;
        float bendDamping;
        bool isometric;
        bool fixedEffectiveMass;
        bool warmStart;
};

struct B2_API b2RopeDef
{
        b2RopeDef()
        {
                position.SetZero();
                vertices = nullptr;
                count = 0;
                masses = nullptr;
                gravity.SetZero();
        }

        b2Vec2 position;
        b2Vec2* vertices;
        int32 count;
        float* masses;
        b2Vec2 gravity;
        b2RopeTuning tuning;
};

class B2_API b2Rope
{
public:
        b2Rope();
        ~b2Rope();

        void Create(const b2RopeDef& def);

        void SetTuning(const b2RopeTuning& tuning);

        void Step(float timeStep, int32 iterations, const b2Vec2& position);

        void Reset(const b2Vec2& position);

        void Draw(b2Draw* draw) const;

private:

        void SolveStretch_PBD();
        void SolveStretch_XPBD(float dt);
        void SolveBend_PBD_Angle();
        void SolveBend_XPBD_Angle(float dt);
        void SolveBend_PBD_Distance();
        void SolveBend_PBD_Height();
        void SolveBend_PBD_Triangle();
        void ApplyBendForces(float dt);

        b2Vec2 m_position;

        int32 m_count;
        int32 m_stretchCount;
        int32 m_bendCount;

        b2RopeStretch* m_stretchConstraints;
        b2RopeBend* m_bendConstraints;

        b2Vec2* m_bindPositions;
        b2Vec2* m_ps;
        b2Vec2* m_p0s;
        b2Vec2* m_vs;

        float* m_invMasses;
        b2Vec2 m_gravity;

        b2RopeTuning m_tuning;
};

#endif