JUCE/examples/Assets/Box2DTests/Breakable.h

/*
* Copyright (c) 2008-2009 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 BREAKABLE_TEST_H
#define BREAKABLE_TEST_H

// This is used to test sensor shapes.
class Breakable : public Test
{
public:

    enum
    {
        e_count = 7
    };

    Breakable()
    {
        // Ground body
        {
            b2BodyDef bd;
            b2Body* ground = m_world->CreateBody(&bd);

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

        // Breakable dynamic body
        {
            b2BodyDef bd;
            bd.type = b2_dynamicBody;
            bd.position.Set(0.0f, 40.0f);
            bd.angle = 0.25f * b2_pi;
            m_body1 = m_world->CreateBody(&bd);

            m_shape1.SetAsBox(0.5f, 0.5f, b2Vec2(-0.5f, 0.0f), 0.0f);
            m_piece1 = m_body1->CreateFixture(&m_shape1, 1.0f);

            m_shape2.SetAsBox(0.5f, 0.5f, b2Vec2(0.5f, 0.0f), 0.0f);
            m_piece2 = m_body1->CreateFixture(&m_shape2, 1.0f);
        }

        m_break = false;
        m_broke = false;
    }

    void PostSolve(b2Contact* contact, const b2ContactImpulse* impulse)
    {
        if (m_broke)
        {
            // The body already broke.
            return;
        }

        // Should the body break?
        int32 count = contact->GetManifold()->pointCount;

        float32 maxImpulse = 0.0f;
        for (int32 i = 0; i < count; ++i)
        {
            maxImpulse = b2Max(maxImpulse, impulse->normalImpulses[i]);
        }

        if (maxImpulse > 40.0f)
        {
            // Flag the body for breaking.
            m_break = true;
        }
    }

    void Break()
    {
        // Create two bodies from one.
        b2Body* body1 = m_piece1->GetBody();
        b2Vec2 center = body1->GetWorldCenter();

        body1->DestroyFixture(m_piece2);
        m_piece2 = NULL;

        b2BodyDef bd;
        bd.type = b2_dynamicBody;
        bd.position = body1->GetPosition();
        bd.angle = body1->GetAngle();

        b2Body* body2 = m_world->CreateBody(&bd);
        m_piece2 = body2->CreateFixture(&m_shape2, 1.0f);

        // Compute consistent velocities for new bodies based on
        // cached velocity.
        b2Vec2 center1 = body1->GetWorldCenter();
        b2Vec2 center2 = body2->GetWorldCenter();

        b2Vec2 velocity1 = m_velocity + b2Cross(m_angularVelocity, center1 - center);
        b2Vec2 velocity2 = m_velocity + b2Cross(m_angularVelocity, center2 - center);

        body1->SetAngularVelocity(m_angularVelocity);
        body1->SetLinearVelocity(velocity1);

        body2->SetAngularVelocity(m_angularVelocity);
        body2->SetLinearVelocity(velocity2);
    }

    void Step(Settings* settings)
    {
        if (m_break)
        {
            Break();
            m_broke = true;
            m_break = false;
        }

        // Cache velocities to improve movement on breakage.
        if (m_broke == false)
        {
            m_velocity = m_body1->GetLinearVelocity();
            m_angularVelocity = m_body1->GetAngularVelocity();
        }

        Test::Step(settings);
    }

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

    b2Body* m_body1;
    b2Vec2 m_velocity;
    float32 m_angularVelocity;
    b2PolygonShape m_shape1;
    b2PolygonShape m_shape2;
    b2Fixture* m_piece1;
    b2Fixture* m_piece2;

    bool m_broke;
    bool m_break;
};

#endif