wrecking_ball.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"

class WreckingBall : public Test
{
public:
        WreckingBall()
        {
                b2Body* ground = NULL;
                {
                        b2BodyDef bd;
                        ground = m_world->CreateBody(&bd);

                        b2EdgeShape shape;
                        shape.SetTwoSided(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 float y = 15.0f;
                        m_distanceJointDef.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)
                                {
                                        bd.position.Set(1.0f * i, y);
                                        bd.angularDamping = 0.4f;
                                }

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

                                if (i == N - 1)
                                {
                                        b2CircleShape circleShape;
                                        circleShape.m_radius = 1.5f;
                                        b2FixtureDef sfd;
                                        sfd.shape = &circleShape;
                                        sfd.density = 100.0f;
                                        sfd.filter.categoryBits = 0x0002;
                                        body->CreateFixture(&sfd);
                                }
                                else
                                {
                                        body->CreateFixture(&fd);
                                }

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

                                prevBody = body;
                        }

                        m_distanceJointDef.localAnchorB.SetZero();

                        float extraLength = 0.01f;
                        m_distanceJointDef.minLength = 0.0f;
                        m_distanceJointDef.maxLength = N - 1.0f + extraLength;
                        m_distanceJointDef.bodyB = prevBody;
                }

                {
                        m_distanceJointDef.bodyA = ground;
                        m_distanceJoint = m_world->CreateJoint(&m_distanceJointDef);
                        m_stabilize = true;
                }
        }

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

                if (ImGui::Checkbox("Stabilize", &m_stabilize))
                {
                        if (m_stabilize == true && m_distanceJoint == nullptr)
                        {
                                m_distanceJoint = m_world->CreateJoint(&m_distanceJointDef);
                        }
                        else if (m_stabilize == false && m_distanceJoint != nullptr)
                        {
                                m_world->DestroyJoint(m_distanceJoint);
                                m_distanceJoint = nullptr;
                        }
                }

                ImGui::End();
        }

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

                if (m_distanceJoint)
                {
                        g_debugDraw.DrawString(5, m_textLine, "Distance Joint ON");
                }
                else
                {
                        g_debugDraw.DrawString(5, m_textLine, "Distance Joint OFF");
                }
                m_textLine += m_textIncrement;
        }

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

        b2DistanceJointDef m_distanceJointDef;
        b2Joint* m_distanceJoint;
        bool m_stabilize;
};

static int testIndex = RegisterTest("Examples", "Wrecking Ball", WreckingBall::Create);