JUCE/examples/Demo/Source/Demos/Box2DTests/RopeJoint.h

/*
* Copyright (c) 2006-2010 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#ifndef ROPE_JOINT_H
#define ROPE_JOINT_H

/// This test shows how a rope joint can be used to stabilize a chain of
/// bodies with a heavy payload. Notice that the rope joint just prevents
/// excessive stretching and has no other effect.
/// By disabling the rope joint you can see that the Box2D solver has trouble
/// supporting heavy bodies with light bodies. Try playing around with the
/// densities, time step, and iterations to see how they affect stability.
/// This test also shows how to use contact filtering. Filtering is configured
/// so that the payload does not collide with the chain.
class RopeJoint : public Test
{
public:
    RopeJoint()
    {
        b2Body* ground = NULL;
        {
            b2BodyDef bd;
            ground = m_world->CreateBody(&bd);

            b2EdgeShape shape;
            shape.Set(b2Vec2(-40.0f, 0.0f), b2Vec2(40.0f, 0.0f));
            ground->CreateFixture(&shape, 0.0f);
        }

        {
            b2PolygonShape shape;
            shape.SetAsBox(0.5f, 0.125f);

            b2FixtureDef fd;
            fd.shape = &shape;
            fd.density = 20.0f;
            fd.friction = 0.2f;
            fd.filter.categoryBits = 0x0001;
            fd.filter.maskBits = 0xFFFF & ~0x0002;

            b2RevoluteJointDef jd;
            jd.collideConnected = false;

            const int32 N = 10;
            const float32 y = 15.0f;
            m_ropeDef.localAnchorA.Set(0.0f, y);

            b2Body* prevBody = ground;
            for (int32 i = 0; i < N; ++i)
            {
                b2BodyDef bd;
                bd.type = b2_dynamicBody;
                bd.position.Set(0.5f + 1.0f * i, y);
                if (i == N - 1)
                {
                    shape.SetAsBox(1.5f, 1.5f);
                    fd.density = 100.0f;
                    fd.filter.categoryBits = 0x0002;
                    bd.position.Set(1.0f * i, y);
                    bd.angularDamping = 0.4f;
                }

                b2Body* body = m_world->CreateBody(&bd);

                body->CreateFixture(&fd);

                b2Vec2 anchor(float32(i), y);
                jd.Initialize(prevBody, body, anchor);
                m_world->CreateJoint(&jd);

                prevBody = body;
            }

            m_ropeDef.localAnchorB.SetZero();

            float32 extraLength = 0.01f;
            m_ropeDef.maxLength = N - 1.0f + extraLength;
            m_ropeDef.bodyB = prevBody;
        }

        {
            m_ropeDef.bodyA = ground;
            m_rope = m_world->CreateJoint(&m_ropeDef);
        }
    }

    void Keyboard(unsigned char key)
    {
        switch (key)
        {
        case 'j':
            if (m_rope)
            {
                m_world->DestroyJoint(m_rope);
                m_rope = NULL;
            }
            else
            {
                m_rope = m_world->CreateJoint(&m_ropeDef);
            }
            break;
        }
    }

    void Step(Settings* settings)
    {
        Test::Step(settings);
        m_debugDraw.DrawString(5, m_textLine, "Press (j) to toggle the rope joint.");
        m_textLine += 15;
        if (m_rope)
        {
            m_debugDraw.DrawString(5, m_textLine, "Rope ON");
        }
        else
        {
            m_debugDraw.DrawString(5, m_textLine, "Rope OFF");
        }
        m_textLine += 15;
    }

    static Test* Create()
    {
        return new RopeJoint;
    }

    b2RopeJointDef m_ropeDef;
    b2Joint* m_rope;
};

#endif