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42 #include "qquickfriction_p.h"
45 \qmlclass Friction QQuickFrictionAffector
46 \inqmlmodule QtQuick.Particles 2
48 \brief The Friction affector slows down movement proportional to the particle's current speed.
53 \qmlproperty real QtQuick.Particles2::Friction::factor
55 A drag will be applied to moving objects which is this factor of their current velocity.
58 \qmlproperty real QtQuick.Particles2::Friction::threshold
60 The drag will only be applied to objects with a velocity above the threshold velocity. The
61 drag applied will bring objects down to the threshold velocity, but no further.
63 The default threshold is 0
65 static qreal sign(qreal a)
67 return a >= 0 ? 1 : -1;
70 static const qreal epsilon = 0.00001;
72 QQuickFrictionAffector::QQuickFrictionAffector(QQuickItem *parent) :
73 QQuickParticleAffector(parent), m_factor(0.0), m_threshold(0.0)
77 bool QQuickFrictionAffector::affectParticle(QQuickParticleData *d, qreal dt)
81 qreal curVX = d->curVX();
82 qreal curVY = d->curVY();
85 qreal newVX = curVX + (curVX * m_factor * -1 * dt);
86 qreal newVY = curVY + (curVY * m_factor * -1 * dt);
89 if (sign(curVX) != sign(newVX))
91 if (sign(curVY) != sign(newVY))
94 qreal curMag = sqrt(curVX*curVX + curVY*curVY);
95 if (curMag <= m_threshold + epsilon)
97 qreal newMag = sqrt(newVX*newVX + newVY*newVY);
98 if (newMag <= m_threshold + epsilon || //went past the threshold, stop there instead
99 sign(curVX) != sign(newVX) || //went so far past maybe it came out the other side!
100 sign(curVY) != sign(newVY)) {
101 qreal theta = atan2(curVY, curVX);
102 newVX = m_threshold * cos(theta);
103 newVY = m_threshold * sin(theta);
107 d->setInstantaneousVX(newVX);
108 d->setInstantaneousVY(newVY);