sensor.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 "imgui/imgui.h"

// This shows how to use sensor shapes. Sensors don't have collision, but report overlap events.
class Sensors : public Test
{
public:

        enum
        {
                e_count = 7
        };

        Sensors()
        {
                {
                        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);
                        }

#if 0
                        {
                                b2FixtureDef sd;
                                sd.SetAsBox(10.0f, 2.0f, b2Vec2(0.0f, 20.0f), 0.0f);
                                sd.isSensor = true;
                                m_sensor = ground->CreateFixture(&sd);
                        }
#else
                        {
                                b2CircleShape shape;
                                shape.m_radius = 5.0f;
                                shape.m_p.Set(0.0f, 10.0f);

                                b2FixtureDef fd;
                                fd.shape = &shape;
                                fd.isSensor = true;
                                m_sensor = ground->CreateFixture(&fd);
                        }
#endif
                }

                {
                        b2CircleShape shape;
                        shape.m_radius = 1.0f;

                        for (int32 i = 0; i < e_count; ++i)
                        {
                                b2BodyDef bd;
                                bd.type = b2_dynamicBody;
                                bd.position.Set(-10.0f + 3.0f * i, 20.0f);
                                bd.userData.pointer = i;

                                m_touching[i] = false;
                                m_bodies[i] = m_world->CreateBody(&bd);

                                m_bodies[i]->CreateFixture(&shape, 1.0f);
                        }
                }

                m_force = 100.0f;
        }

        // Implement contact listener.
        void BeginContact(b2Contact* contact) override
        {
                b2Fixture* fixtureA = contact->GetFixtureA();
                b2Fixture* fixtureB = contact->GetFixtureB();

                if (fixtureA == m_sensor)
                {
                        uintptr_t index = fixtureB->GetBody()->GetUserData().pointer;
                        if (index < e_count)
                        {
                                m_touching[index] = true;
                        }
                }

                if (fixtureB == m_sensor)
                {
                        uintptr_t index = fixtureA->GetBody()->GetUserData().pointer;
                        if (index < e_count)
                        {
                                m_touching[index] = true;
                        }
                }
        }

        // Implement contact listener.
        void EndContact(b2Contact* contact) override
        {
                b2Fixture* fixtureA = contact->GetFixtureA();
                b2Fixture* fixtureB = contact->GetFixtureB();

                if (fixtureA == m_sensor)
                {
                        uintptr_t index = fixtureB->GetBody()->GetUserData().pointer;
                        if (index < e_count)
                        {
                                m_touching[index] = false;
                        }
                }

                if (fixtureB == m_sensor)
                {
                        uintptr_t index = fixtureA->GetBody()->GetUserData().pointer;
                        if (index < e_count)
                        {
                                m_touching[index] = false;
                        }
                }
        }

        void UpdateUI() override
        {
                ImGui::SetNextWindowPos(ImVec2(10.0f, 100.0f));
                ImGui::SetNextWindowSize(ImVec2(200.0f, 60.0f));
                ImGui::Begin("Sensor Controls", nullptr, ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize);

                ImGui::SliderFloat("Force", &m_force, 0.0f, 2000.0f, "%.0f");

                ImGui::End();
        }

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

                // Traverse the contact results. Apply a force on shapes
                // that overlap the sensor.
                for (int32 i = 0; i < e_count; ++i)
                {
                        if (m_touching[i] == false)
                        {
                                continue;
                        }

                        b2Body* body = m_bodies[i];
                        b2Body* ground = m_sensor->GetBody();

                        b2CircleShape* circle = (b2CircleShape*)m_sensor->GetShape();
                        b2Vec2 center = ground->GetWorldPoint(circle->m_p);

                        b2Vec2 position = body->GetPosition();

                        b2Vec2 d = center - position;
                        if (d.LengthSquared() < FLT_EPSILON * FLT_EPSILON)
                        {
                                continue;
                        }

                        d.Normalize();
                        b2Vec2 F = m_force * d;
                        body->ApplyForce(F, position, false);
                }
        }

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

        b2Fixture* m_sensor;
        b2Body* m_bodies[e_count];
        float m_force;
        bool m_touching[e_count];
};

static int testIndex = RegisterTest("Collision", "Sensors", Sensors::Create);