motor_joint.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 "settings.h"
#include "test.h"

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

                        b2EdgeShape shape;
                        shape.SetTwoSided(b2Vec2(-20.0f, 0.0f), b2Vec2(20.0f, 0.0f));

                        b2FixtureDef fd;
                        fd.shape = &shape;

                        ground->CreateFixture(&fd);
                }

                // Define motorized body
                {
                        b2BodyDef bd;
                        bd.type = b2_dynamicBody;
                        bd.position.Set(0.0f, 8.0f);
                        b2Body* body = m_world->CreateBody(&bd);

                        b2PolygonShape shape;
                        shape.SetAsBox(2.0f, 0.5f);

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.friction = 0.6f;
                        fd.density = 2.0f;
                        body->CreateFixture(&fd);

                        b2MotorJointDef mjd;
                        mjd.Initialize(ground, body);
                        mjd.maxForce = 1000.0f;
                        mjd.maxTorque = 1000.0f;
                        m_joint = (b2MotorJoint*)m_world->CreateJoint(&mjd);
                }

                m_go = false;
                m_time = 0.0f;
        }

        void Keyboard(int key) override
        {
                switch (key)
                {
                case GLFW_KEY_S:
                        m_go = !m_go;
                        break;
                }
        }

        void Step(Settings& settings) override
        {
                if (m_go && settings.m_hertz > 0.0f)
                {
                        m_time += 1.0f / settings.m_hertz;
                }

                b2Vec2 linearOffset;
                linearOffset.x = 6.0f * sinf(2.0f * m_time);
                linearOffset.y = 8.0f + 4.0f * sinf(1.0f * m_time);
                
                float angularOffset = 4.0f * m_time;

                m_joint->SetLinearOffset(linearOffset);
                m_joint->SetAngularOffset(angularOffset);

                g_debugDraw.DrawPoint(linearOffset, 4.0f, b2Color(0.9f, 0.9f, 0.9f));

                Test::Step(settings);
                g_debugDraw.DrawString(5, m_textLine, "Keys: (s) pause");
                m_textLine += 15;
        }

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

        b2MotorJoint* m_joint;
        float m_time;
        bool m_go;
};

static int testIndex = RegisterTest("Joints", "Motor Joint", MotorJoint::Create);