axmol/tests/cpp-tests/Classes/Box2DTestBed/tests/cantilever.cpp

// 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);