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++ // Copyright (C) 2026 The Qt Company Ltd.
++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
++
++ #include "qflexiblejoint_p.h"
++
++ #include <extensions/PxJoint.h>
++
++ QT_BEGIN_NAMESPACE
++
++ /*!
++ \qmltype FlexibleJoint
++ \inqmlmodule QtQuick3D.Physics
++ \since 6.13
++ \inherits PhysicsJoint
++ \brief Base type for flexible joints with configurable spring stiffness and damping.
++
++ This is the abstract base type for all joints that support customizable spring stiffness
++ and damping factors for soft constraints and joint limits.
++
++ Whether a joint limit is hard or soft, and how it behaves when soft, depends on the
++ combination of \l stiffness and \l damping, as seen in the following table:
++
++ \table
++ \header
++ \li \l stiffness
++ \li \l damping
++ \li Behavior
++ \row
++ \li \c 0.0
++ \li \c 0.0
++ \li Hard constraint: the limit cannot be penetrated (the default).
++ \row
++ \li greater than \c 0.0
++ \li \c 0.0
++ \li Soft spring, undamped: the body bounces against the limit indefinitely.
++ \row
++ \li greater than \c 0.0
++ \li greater than \c 0.0
++ \li Soft spring, damped: the body bounces against the limit and settles.
++ \row
++ \li \c 0.0
++ \li greater than \c 0.0
++ \li Soft, viscous drag only: motion is resisted, but no positional restoring force is
++ applied.
++ \endtable
++
++ \note At least one of the connected bodies needs to be dynamic.
++
++ \sa {FixedJoint}
++ \sa {DistanceJoint}
++ \sa {PrismaticJoint}
++ \sa {RevoluteJoint}
++ \sa {SphericalJoint}
++ \sa {D6Joint}
++ */
++
++ /*!
++ \qmlproperty real FlexibleJoint::stiffness
++ \since 6.13
++ \default 0.0
++
++ This property holds the spring stiffness for joint limits. See the table above for how it
++ combines with \l damping to determine whether the limit is hard or soft.
++
++ When greater than \c 0.0, the higher the value, the stronger the restorative force pulling
++ the body back once it crosses the limit boundary, and the less penetration is allowed before
++ the body is pushed back. The right value depends on the mass and geometry of the connected
++ bodies. A value that feels stiff for a light body with a short lever arm may feel soft for a
++ heavier body or a longer lever arm, so start from a small value and increase it until the
++ limit feels sufficiently rigid for your scene.
++
++ Range: \c{[0, \inf)}
++
++ \sa damping, PhysicsWorld::typicalLength, PhysicsWorld::defaultDensity
++ */
++
++ /*!
++ \qmlproperty real FlexibleJoint::damping
++ \since 6.13
++ \default 0.0
++
++ This property holds the energy dissipation (damping factor) for soft joint limits. See the
++ table above for how it combines with \l stiffness to determine whether the limit is hard or
++ soft.
++
++ When \l stiffness is greater than \c 0.0, this property controls how quickly oscillations
++ around the limit boundary settle: with \c 0.0 (the default), no energy is lost and the body
++ bounces indefinitely; increasing the value suppresses the bounce, though too little leaves
++ the body oscillating before it settles, while too much makes the motion near the limit feel
++ heavy or sluggish.
++
++ When \l stiffness is \c 0.0, this property instead applies a resistive (viscous) force with
++ no positional restoring effect.
++
++ Range: \c{[0, \inf)}
++
++ \sa stiffness, PhysicsWorld::typicalLength, PhysicsWorld::defaultDensity
++ */
++
++ float QFlexibleJoint::stiffness() const
++ {
++ return m_stiffness;
++ }
++
++ void QFlexibleJoint::setStiffness(float stiffness)
++ {
++ stiffness = qMax(0.f, stiffness);
++ if (qFuzzyCompare(m_stiffness, stiffness))
++ return;
++ m_stiffness = stiffness;
++ m_dirtyProperties = true;
++ emit stiffnessChanged();
++ }
++
++ float QFlexibleJoint::damping() const
++ {
++ return m_damping;
++ }
++
++ void QFlexibleJoint::setDamping(float damping)
++ {
++ damping = qMax(0.f, damping);
++ if (qFuzzyCompare(m_damping, damping))
++ return;
++ m_damping = damping;
++ m_dirtyProperties = true;
++ emit dampingChanged();
++ }
++
++ QT_END_NAMESPACE