collision_processing.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"

#include <algorithm>

// This test shows collision processing and tests
// deferred body destruction.
class CollisionProcessing : public Test
{
public:
        CollisionProcessing()
        {
                // Ground body
                {
                        b2EdgeShape shape;
                        shape.SetTwoSided(b2Vec2(-50.0f, 0.0f), b2Vec2(50.0f, 0.0f));

                        b2FixtureDef sd;
                        sd.shape = &shape;;

                        b2BodyDef bd;
                        b2Body* ground = m_world->CreateBody(&bd);
                        ground->CreateFixture(&sd);
                }

                float xLo = -5.0f, xHi = 5.0f;
                float yLo = 2.0f, yHi = 35.0f;

                // Small triangle
                b2Vec2 vertices[3];
                vertices[0].Set(-1.0f, 0.0f);
                vertices[1].Set(1.0f, 0.0f);
                vertices[2].Set(0.0f, 2.0f);

                b2PolygonShape polygon;
                polygon.Set(vertices, 3);

                b2FixtureDef triangleShapeDef;
                triangleShapeDef.shape = &polygon;
                triangleShapeDef.density = 1.0f;

                b2BodyDef triangleBodyDef;
                triangleBodyDef.type = b2_dynamicBody;
                triangleBodyDef.position.Set(RandomFloat(xLo, xHi), RandomFloat(yLo, yHi));

                b2Body* body1 = m_world->CreateBody(&triangleBodyDef);
                body1->CreateFixture(&triangleShapeDef);

                // Large triangle (recycle definitions)
                vertices[0] *= 2.0f;
                vertices[1] *= 2.0f;
                vertices[2] *= 2.0f;
                polygon.Set(vertices, 3);

                triangleBodyDef.position.Set(RandomFloat(xLo, xHi), RandomFloat(yLo, yHi));

                b2Body* body2 = m_world->CreateBody(&triangleBodyDef);
                body2->CreateFixture(&triangleShapeDef);
                
                // Small box
                polygon.SetAsBox(1.0f, 0.5f);

                b2FixtureDef boxShapeDef;
                boxShapeDef.shape = &polygon;
                boxShapeDef.density = 1.0f;

                b2BodyDef boxBodyDef;
                boxBodyDef.type = b2_dynamicBody;
                boxBodyDef.position.Set(RandomFloat(xLo, xHi), RandomFloat(yLo, yHi));

                b2Body* body3 = m_world->CreateBody(&boxBodyDef);
                body3->CreateFixture(&boxShapeDef);

                // Large box (recycle definitions)
                polygon.SetAsBox(2.0f, 1.0f);
                boxBodyDef.position.Set(RandomFloat(xLo, xHi), RandomFloat(yLo, yHi));
                
                b2Body* body4 = m_world->CreateBody(&boxBodyDef);
                body4->CreateFixture(&boxShapeDef);

                // Small circle
                b2CircleShape circle;
                circle.m_radius = 1.0f;

                b2FixtureDef circleShapeDef;
                circleShapeDef.shape = &circle;
                circleShapeDef.density = 1.0f;

                b2BodyDef circleBodyDef;
                circleBodyDef.type = b2_dynamicBody;
                circleBodyDef.position.Set(RandomFloat(xLo, xHi), RandomFloat(yLo, yHi));

                b2Body* body5 = m_world->CreateBody(&circleBodyDef);
                body5->CreateFixture(&circleShapeDef);

                // Large circle
                circle.m_radius *= 2.0f;
                circleBodyDef.position.Set(RandomFloat(xLo, xHi), RandomFloat(yLo, yHi));

                b2Body* body6 = m_world->CreateBody(&circleBodyDef);
                body6->CreateFixture(&circleShapeDef);
        }

        void Step(Settings& settings) override
        {
                Test::Step(settings);

                // We are going to destroy some bodies according to contact
                // points. We must buffer the bodies that should be destroyed
                // because they may belong to multiple contact points.
                const int32 k_maxNuke = 6;
                b2Body* nuke[k_maxNuke];
                int32 nukeCount = 0;

                // Traverse the contact results. Destroy bodies that
                // are touching heavier bodies.
                for (int32 i = 0; i < m_pointCount; ++i)
                {
                        ContactPoint* point = m_points + i;

                        b2Body* body1 = point->fixtureA->GetBody();
                        b2Body* body2 = point->fixtureB->GetBody();
                        float mass1 = body1->GetMass();
                        float mass2 = body2->GetMass();

                        if (mass1 > 0.0f && mass2 > 0.0f)
                        {
                                if (mass2 > mass1)
                                {
                                        nuke[nukeCount++] = body1;
                                }
                                else
                                {
                                        nuke[nukeCount++] = body2;
                                }

                                if (nukeCount == k_maxNuke)
                                {
                                        break;
                                }
                        }
                }

                // Sort the nuke array to group duplicates.
                std::sort(nuke, nuke + nukeCount);

                // Destroy the bodies, skipping duplicates.
                int32 i = 0;
                while (i < nukeCount)
                {
                        b2Body* b = nuke[i++];
                        while (i < nukeCount && nuke[i] == b)
                        {
                                ++i;
                        }

                        if (b != m_bomb)
                        {
                                m_world->DestroyBody(b);
                        }
                }
        }

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

static int testIndex = RegisterTest("Examples", "Collision Processing", CollisionProcessing::Create);