cantilever.cpp

Go to the documentation of this file.

// 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"

// It is difficult to make a cantilever made of links completely rigid with weld joints.
// You will have to use a high number of iterations to make them stiff.
// So why not go ahead and use soft weld joints? They behave like a revolute
// joint with a rotational spring.
class Cantilever : public Test
{
public:

        enum
        {
                e_count = 8
        };

        Cantilever()
        {
                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;

                        b2WeldJointDef jd;

                        b2Body* prevBody = ground;
                        for (int32 i = 0; i < e_count; ++i)
                        {
                                b2BodyDef bd;
                                bd.type = b2_dynamicBody;
                                bd.position.Set(-14.5f + 1.0f * i, 5.0f);
                                b2Body* body = m_world->CreateBody(&bd);
                                body->CreateFixture(&fd);

                                b2Vec2 anchor(-15.0f + 1.0f * i, 5.0f);
                                jd.Initialize(prevBody, body, anchor);
                                m_world->CreateJoint(&jd);

                                prevBody = body;
                        }
                }

                {
                        b2PolygonShape shape;
                        shape.SetAsBox(1.0f, 0.125f);

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 20.0f;

                        b2WeldJointDef jd;
                        float frequencyHz = 5.0f;
                        float dampingRatio = 0.7f;

                        b2Body* prevBody = ground;
                        for (int32 i = 0; i < 3; ++i)
                        {
                                b2BodyDef bd;
                                bd.type = b2_dynamicBody;
                                bd.position.Set(-14.0f + 2.0f * i, 15.0f);
                                b2Body* body = m_world->CreateBody(&bd);
                                body->CreateFixture(&fd);

                                b2Vec2 anchor(-15.0f + 2.0f * i, 15.0f);
                                jd.Initialize(prevBody, body, anchor);
                                b2AngularStiffness(jd.stiffness, jd.damping, frequencyHz, dampingRatio, jd.bodyA, jd.bodyB);
                                m_world->CreateJoint(&jd);

                                prevBody = body;
                        }
                }

                {
                        b2PolygonShape shape;
                        shape.SetAsBox(0.5f, 0.125f);

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 20.0f;

                        b2WeldJointDef jd;

                        b2Body* prevBody = ground;
                        for (int32 i = 0; i < e_count; ++i)
                        {
                                b2BodyDef bd;
                                bd.type = b2_dynamicBody;
                                bd.position.Set(-4.5f + 1.0f * i, 5.0f);
                                b2Body* body = m_world->CreateBody(&bd);
                                body->CreateFixture(&fd);

                                if (i > 0)
                                {
                                        b2Vec2 anchor(-5.0f + 1.0f * i, 5.0f);
                                        jd.Initialize(prevBody, body, anchor);
                                        m_world->CreateJoint(&jd);
                                }

                                prevBody = body;
                        }
                }

                {
                        b2PolygonShape shape;
                        shape.SetAsBox(0.5f, 0.125f);

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 20.0f;

                        b2WeldJointDef jd;
                        float frequencyHz = 8.0f;
                        float dampingRatio = 0.7f;

                        b2Body* prevBody = ground;
                        for (int32 i = 0; i < e_count; ++i)
                        {
                                b2BodyDef bd;
                                bd.type = b2_dynamicBody;
                                bd.position.Set(5.5f + 1.0f * i, 10.0f);
                                b2Body* body = m_world->CreateBody(&bd);
                                body->CreateFixture(&fd);

                                if (i > 0)
                                {
                                        b2Vec2 anchor(5.0f + 1.0f * i, 10.0f);
                                        jd.Initialize(prevBody, body, anchor);

                                        b2AngularStiffness(jd.stiffness, jd.damping, frequencyHz, dampingRatio, prevBody, body);

                                        m_world->CreateJoint(&jd);
                                }

                                prevBody = body;
                        }
                }

                for (int32 i = 0; i < 2; ++i)
                {
                        b2Vec2 vertices[3];
                        vertices[0].Set(-0.5f, 0.0f);
                        vertices[1].Set(0.5f, 0.0f);
                        vertices[2].Set(0.0f, 1.5f);

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

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 1.0f;

                        b2BodyDef bd;
                        bd.type = b2_dynamicBody;
                        bd.position.Set(-8.0f + 8.0f * i, 12.0f);
                        b2Body* body = m_world->CreateBody(&bd);
                        body->CreateFixture(&fd);
                }

                for (int32 i = 0; i < 2; ++i)
                {
                        b2CircleShape shape;
                        shape.m_radius = 0.5f;

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 1.0f;

                        b2BodyDef bd;
                        bd.type = b2_dynamicBody;
                        bd.position.Set(-6.0f + 6.0f * i, 10.0f);
                        b2Body* body = m_world->CreateBody(&bd);
                        body->CreateFixture(&fd);
                }
        }

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

        b2Body* m_middle;
};

static int testIndex = RegisterTest("Joints", "Cantilever", Cantilever::Create);