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[blok] / Box2D / Source / Dynamics / Joints / b2MouseJoint.h

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+/*
+* Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
+*
+* This software is provided 'as-is', without any express or implied
+* warranty.  In no event will the authors be held liable for any damages
+* arising from the use of this software.
+* Permission is granted to anyone to use this software for any purpose,
+* including commercial applications, and to alter it and redistribute it
+* freely, subject to the following restrictions:
+* 1. The origin of this software must not be misrepresented; you must not
+* claim that you wrote the original software. If you use this software
+* in a product, an acknowledgment in the product documentation would be
+* appreciated but is not required.
+* 2. Altered source versions must be plainly marked as such, and must not be
+* misrepresented as being the original software.
+* 3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef B2_MOUSE_JOINT_H
+#define B2_MOUSE_JOINT_H
+
+#include "b2Joint.h"
+
+/// Mouse joint definition. This requires a world target point,
+/// tuning parameters, and the time step.
+struct b2MouseJointDef : public b2JointDef
+{
+       b2MouseJointDef()
+       {
+               type = e_mouseJoint;
+               target.Set(0.0f, 0.0f);
+               maxForce = 0.0f;
+               frequencyHz = 5.0f;
+               dampingRatio = 0.7f;
+               timeStep = 1.0f / 60.0f;
+       }
+
+       /// The initial world target point. This is assumed
+       /// to coincide with the body anchor initially.
+       b2Vec2 target;
+
+       /// The maximum constraint force that can be exerted
+       /// to move the candidate body. Usually you will express
+       /// as some multiple of the weight (multiplier * mass * gravity).
+       float32 maxForce;
+
+       /// The response speed.
+       float32 frequencyHz;
+
+       /// The damping ratio. 0 = no damping, 1 = critical damping.
+       float32 dampingRatio;
+
+       /// The time step used in the simulation.
+       float32 timeStep;
+};
+
+/// A mouse joint is used to make a point on a body track a
+/// specified world point. This a soft constraint with a maximum
+/// force. This allows the constraint to stretch and without
+/// applying huge forces.
+class b2MouseJoint : public b2Joint
+{
+public:
+
+       /// Implements b2Joint.
+       b2Vec2 GetAnchor1() const;
+
+       /// Implements b2Joint.
+       b2Vec2 GetAnchor2() const;
+
+       /// Implements b2Joint.
+       b2Vec2 GetReactionForce() const;
+
+       /// Implements b2Joint.
+       float32 GetReactionTorque() const;
+
+       /// Use this to update the target point.
+       void SetTarget(const b2Vec2& target);
+
+       //--------------- Internals Below -------------------
+
+       b2MouseJoint(const b2MouseJointDef* def);
+
+       void InitVelocityConstraints(const b2TimeStep& step);
+       void SolveVelocityConstraints(const b2TimeStep& step);
+       bool SolvePositionConstraints()
+       {
+               return true;
+       }
+
+       b2Vec2 m_localAnchor;
+       b2Vec2 m_target;
+       b2Vec2 m_impulse;
+
+       b2Mat22 m_mass;         // effective mass for point-to-point constraint.
+       b2Vec2 m_C;                             // position error
+       float32 m_maxForce;
+       float32 m_beta;                 // bias factor
+       float32 m_gamma;                // softness
+};
+
+#endif