path: root/src/declarative/util/qdeclarativespringfollow.cpp

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#include "qdeclarativespringfollow_p.h"

#include "qdeclarativeanimation_p_p.h"

#include <QtCore/qdebug.h>

#include <private/qobject_p.h>

#include <limits.h>
#include <math.h>

QT_BEGIN_NAMESPACE



class QDeclarativeSpringFollowPrivate : public QObjectPrivate
{
    Q_DECLARE_PUBLIC(QDeclarativeSpringFollow)
public:
    QDeclarativeSpringFollowPrivate()
        : currentValue(0), sourceValue(0), maxVelocity(0), lastTime(0)
        , mass(1.0), spring(0.), damping(0.), velocity(0), epsilon(0.01)
        , modulus(0.0), useMass(false), haveModulus(false), enabled(true), mode(Track), clock(this) {}

    QDeclarativeProperty property;
    qreal currentValue;
    qreal sourceValue;
    qreal maxVelocity;
    qreal velocityms;
    int lastTime;
    qreal mass;
    qreal spring;
    qreal damping;
    qreal velocity;
    qreal epsilon;
    qreal modulus;

    bool useMass : 1;
    bool haveModulus : 1;
    bool enabled : 1;

    enum Mode {
        Track,
        Velocity,
        Spring
    };
    Mode mode;

    void tick(int);
    void updateMode();
    void start();
    void stop();

    QTickAnimationProxy<QDeclarativeSpringFollowPrivate, &QDeclarativeSpringFollowPrivate::tick> clock;
};

void QDeclarativeSpringFollowPrivate::tick(int time)
{
    Q_Q(QDeclarativeSpringFollow);

    int elapsed = time - lastTime;
    if (!elapsed)
        return;
    qreal srcVal = sourceValue;
    if (haveModulus) {
        currentValue = fmod(currentValue, modulus);
        srcVal = fmod(srcVal, modulus);
    }
    if (mode == Spring) {
        if (elapsed < 16) // capped at 62fps.
            return;
        // Real men solve the spring DEs using RK4.
        // We'll do something much simpler which gives a result that looks fine.
        int count = elapsed / 16;
        for (int i = 0; i < count; ++i) {
            qreal diff = srcVal - currentValue;
            if (haveModulus && qAbs(diff) > modulus / 2) {
                if (diff < 0)
                    diff += modulus;
                else
                    diff -= modulus;
            }
            if (useMass)
                velocity = velocity + (spring * diff - damping * velocity) / mass;
            else
                velocity = velocity + spring * diff - damping * velocity;
            if (maxVelocity > 0.) {
                // limit velocity
                if (velocity > maxVelocity)
                    velocity = maxVelocity;
                else if (velocity < -maxVelocity)
                    velocity = -maxVelocity;
            }
            currentValue += velocity * 16.0 / 1000.0;
            if (haveModulus) {
                currentValue = fmod(currentValue, modulus);
                if (currentValue < 0.0)
                    currentValue += modulus;
            }
        }
        if (qAbs(velocity) < epsilon && qAbs(srcVal - currentValue) < epsilon) {
            velocity = 0.0;
            currentValue = srcVal;
            clock.stop();
        }
        lastTime = time - (elapsed - count * 16);
    } else {
        qreal moveBy = elapsed * velocityms;
        qreal diff = srcVal - currentValue;
        if (haveModulus && qAbs(diff) > modulus / 2) {
            if (diff < 0)
                diff += modulus;
            else
                diff -= modulus;
        }
        if (diff > 0) {
            currentValue += moveBy;
            if (haveModulus)
                currentValue = fmod(currentValue, modulus);
            if (currentValue > sourceValue) {
                currentValue = sourceValue;
                clock.stop();
            }
        } else {
            currentValue -= moveBy;
            if (haveModulus && currentValue < 0.0)
                currentValue = fmod(currentValue, modulus) + modulus;
            if (currentValue < sourceValue) {
                currentValue = sourceValue;
                clock.stop();
            }
        }
        lastTime = time;
    }
    property.write(currentValue);
    emit q->valueChanged(currentValue);
    if (clock.state() != QAbstractAnimation::Running)
        emit q->syncChanged();
}

void QDeclarativeSpringFollowPrivate::updateMode()
{
    if (spring == 0. && maxVelocity == 0.)
        mode = Track;
    else if (spring > 0.)
        mode = Spring;
    else
        mode = Velocity;
}

void QDeclarativeSpringFollowPrivate::start()
{
    if (!enabled)
        return;

    Q_Q(QDeclarativeSpringFollow);
    if (mode == QDeclarativeSpringFollowPrivate::Track) {
        currentValue = sourceValue;
        property.write(currentValue);
    } else if (sourceValue != currentValue && clock.state() != QAbstractAnimation::Running) {
        lastTime = 0;
        currentValue = property.read().toReal();
        clock.start(); // infinity??
        emit q->syncChanged();
    }
}

void QDeclarativeSpringFollowPrivate::stop()
{
    clock.stop();
}

/*!
    \qmlclass SpringFollow QDeclarativeSpringFollow
    \since 4.7
    \brief The SpringFollow element allows a property to track a value.

    In example below, \e rect2 will follow \e rect1 moving with a velocity of up to 200:
    \code
    Rectangle {
        id: rect1
        width: 20; height: 20
        color: "#00ff00"
        y: 200  // initial value
        SequentialAnimation on y {
            loops: Animation.Infinite
            NumberAnimation {
                to: 200
                easing.type: "OutBounce"
                easing.amplitude: 100
                duration: 2000
            }
            PauseAnimation { duration: 1000 }
        }
    }
    Rectangle {
        id: rect2
        x: rect1.width
        width: 20; height: 20
        color: "#ff0000"
        SpringFollow on y { source: rect1.y; velocity: 200 }
    }
    \endcode
*/

QDeclarativeSpringFollow::QDeclarativeSpringFollow(QObject *parent)
: QObject(*(new QDeclarativeSpringFollowPrivate),parent)
{
}

QDeclarativeSpringFollow::~QDeclarativeSpringFollow()
{
}

void QDeclarativeSpringFollow::setTarget(const QDeclarativeProperty &property)
{
    Q_D(QDeclarativeSpringFollow);
    d->property = property;
    d->currentValue = property.read().toReal();
}

qreal QDeclarativeSpringFollow::sourceValue() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->sourceValue;
}

/*!
    \qmlproperty qreal SpringFollow::source
    This property holds the source value which will be tracked.

    Bind to a property in order to track its changes.
*/

void QDeclarativeSpringFollow::setSourceValue(qreal value)
{
    Q_D(QDeclarativeSpringFollow);
    if (d->clock.state() == QAbstractAnimation::Running && d->sourceValue == value)
        return;

    d->sourceValue = value;
    d->start();
}

/*!
    \qmlproperty qreal SpringFollow::velocity
    This property holds the maximum velocity allowed when tracking the source.
*/

qreal QDeclarativeSpringFollow::velocity() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->maxVelocity;
}

void QDeclarativeSpringFollow::setVelocity(qreal velocity)
{
    Q_D(QDeclarativeSpringFollow);
    d->maxVelocity = velocity;
    d->velocityms = velocity / 1000.0;
    d->updateMode();
}

/*!
    \qmlproperty qreal SpringFollow::spring
    This property holds the spring constant

    The spring constant describes how strongly the target is pulled towards the
    source.  Setting spring to 0 turns off spring tracking.  Useful values 0 - 5.0

    When a spring constant is set and the velocity property is greater than 0,
    velocity limits the maximum speed.
*/
qreal QDeclarativeSpringFollow::spring() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->spring;
}

void QDeclarativeSpringFollow::setSpring(qreal spring)
{
    Q_D(QDeclarativeSpringFollow);
    d->spring = spring;
    d->updateMode();
}

/*!
    \qmlproperty qreal SpringFollow::damping
    This property holds the spring damping constant

    The damping constant describes how quickly a sprung follower comes to rest.
    Useful range is 0 - 1.0
*/
qreal QDeclarativeSpringFollow::damping() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->damping;
}

void QDeclarativeSpringFollow::setDamping(qreal damping)
{
    Q_D(QDeclarativeSpringFollow);
    if (damping > 1.)
        damping = 1.;

    d->damping = damping;
}


/*!
    \qmlproperty qreal SpringFollow::epsilon
    This property holds the spring epsilon

    The epsilon is the rate and amount of change in the value which is close enough
    to 0 to be considered equal to zero. This will depend on the usage of the value.
    For pixel positions, 0.25 would suffice. For scale, 0.005 will suffice.

    The default is 0.01. Tuning this value can provide small performance improvements.
*/
qreal QDeclarativeSpringFollow::epsilon() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->epsilon;
}

void QDeclarativeSpringFollow::setEpsilon(qreal epsilon)
{
    Q_D(QDeclarativeSpringFollow);
    d->epsilon = epsilon;
}

/*!
    \qmlproperty qreal SpringFollow::modulus
    This property holds the modulus value.

    Setting a \a modulus forces the target value to "wrap around" at the modulus.
    For example, setting the modulus to 360 will cause a value of 370 to wrap around to 10.
*/
qreal QDeclarativeSpringFollow::modulus() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->modulus;
}

void QDeclarativeSpringFollow::setModulus(qreal modulus)
{
    Q_D(QDeclarativeSpringFollow);
    if (d->modulus != modulus) {
        d->haveModulus = modulus != 0.0;
        d->modulus = modulus;
        emit modulusChanged();
    }
}

/*!
    \qmlproperty qreal SpringFollow::mass
    This property holds the "mass" of the property being moved.

    mass is 1.0 by default.  Setting a different mass changes the dynamics of
    a \l spring follow.
*/
qreal QDeclarativeSpringFollow::mass() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->mass;
}

void QDeclarativeSpringFollow::setMass(qreal mass)
{
    Q_D(QDeclarativeSpringFollow);
    if (d->mass != mass && mass > 0.0) {
        d->useMass = mass != 1.0;
        d->mass = mass;
        emit massChanged();
    }
}

/*!
    \qmlproperty qreal SpringFollow::value
    The current value.
*/

/*!
    \qmlproperty bool SpringFollow::enabled
    This property holds whether the target will track the source.
*/
bool QDeclarativeSpringFollow::enabled() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->enabled;
}

void QDeclarativeSpringFollow::setEnabled(bool enabled)
{
    Q_D(QDeclarativeSpringFollow);
    d->enabled = enabled;
    if (enabled)
        d->start();
    else
        d->stop();
}

/*!
    \qmlproperty bool SpringFollow::inSync
    This property is true when target is equal to the source; otherwise
    false.  If inSync is true the target is not being animated.

    If \l enabled is false then inSync will also be false.
*/
bool QDeclarativeSpringFollow::inSync() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->enabled && d->clock.state() != QAbstractAnimation::Running;
}

qreal QDeclarativeSpringFollow::value() const
{
    Q_D(const QDeclarativeSpringFollow);
    return d->currentValue;
}

QT_END_NAMESPACE