breakable.cpp

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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.

#include "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.SetTwoSided(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) override
        {
                if (m_broke)
                {
                        // The body already broke.
                        return;
                }

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

                float 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) override
        {
                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;
        float m_angularVelocity;
        b2PolygonShape m_shape1;
        b2PolygonShape m_shape2;
        b2Fixture* m_piece1;
        b2Fixture* m_piece2;

        bool m_broke;
        bool m_break;
};

static int testIndex = RegisterTest("Examples", "Breakable", Breakable::Create);