qtdeclarative/src/declarative/particles/qsggravity.cpp

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#include "qsggravity_p.h"
#include <cmath>
QT_BEGIN_NAMESPACE
const qreal CONV = 0.017453292520444443;
/*!
    \qmlclass Gravity QSGGravityAffector
    \inqmlmodule QtQuick.Particles 2
    \inherits Affector
    \brief The Gravity element allows you to set a constant accleration in an angle

    This element will set the acceleration of all affected particles to a vector of
    the specified magnitude in the specified angle. If the angle or acceleration is
    not varying, it is more efficient to set the specified acceleration on the Emitter.

    This element models the gravity of a massive object whose center of
    gravity is far away (and thus the gravitational pull is effectively constant
    across the scene). To model the gravity of an object near or inside the scene,
    use PointAttractor.
*/

/*!
    \qmlproperty real QtQuick.Particles2::Gravity::acceleration

    Pixels per second that objects will be accelerated by.
*/
/*!
    \qmlproperty real QtQuick.Particles2::Gravity::angle

    Angle of acceleration.
*/

QSGGravityAffector::QSGGravityAffector(QQuickItem *parent) :
    QSGParticleAffector(parent), m_acceleration(-10), m_angle(90), m_xAcc(0), m_yAcc(0)
{
    connect(this, SIGNAL(accelerationChanged(qreal)),
            this, SLOT(recalc()));
    connect(this, SIGNAL(angleChanged(qreal)),
            this, SLOT(recalc()));
    recalc();
}

void QSGGravityAffector::recalc()
{
    qreal theta = m_angle * CONV;
    m_xAcc = m_acceleration * cos(theta);
    m_yAcc = m_acceleration * sin(theta);
}

bool QSGGravityAffector::affectParticle(QSGParticleData *d, qreal dt)
{
    Q_UNUSED(dt);
    bool changed = false;
    if (d->ax != m_xAcc){
        d->setInstantaneousAX(m_xAcc);
        changed = true;
    }
    if (d->ay != m_yAcc){
        d->setInstantaneousAY(m_yAcc);
        changed = true;
    }
    return changed;
}
QT_END_NAMESPACE