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39
40#include "qquickfriction_p.h"
41#include <qmath.h>
42
43QT_BEGIN_NAMESPACE
44/*!
45 \qmltype Friction
46 \instantiates QQuickFrictionAffector
47 \inqmlmodule QtQuick.Particles
48 \ingroup qtquick-particles
49 \inherits Affector
50 \brief For applying friction proportional to the particle's current velocity.
51
52*/
53
54/*!
55 \qmlproperty real QtQuick.Particles::Friction::factor
56
57 A drag will be applied to moving objects which is this factor of their current velocity.
58*/
59/*!
60 \qmlproperty real QtQuick.Particles::Friction::threshold
61
62 The drag will only be applied to objects with a velocity above the threshold velocity. The
63 drag applied will bring objects down to the threshold velocity, but no further.
64
65 The default threshold is 0
66*/
67static qreal sign(qreal a)
68{
69 return a >= 0 ? 1 : -1;
70}
71
72static const qreal epsilon = 0.00001;
73
74QQuickFrictionAffector::QQuickFrictionAffector(QQuickItem *parent) :
75 QQuickParticleAffector(parent), m_factor(0.0), m_threshold(0.0)
76{
77}
78
79bool QQuickFrictionAffector::affectParticle(QQuickParticleData *d, qreal dt)
80{
81 if (!m_factor)
82 return false;
83 qreal curVX = d->curVX(particleSystem: m_system);
84 qreal curVY = d->curVY(particleSystem: m_system);
85 if (!curVX && !curVY)
86 return false;
87 qreal newVX = curVX + (curVX * m_factor * -1 * dt);
88 qreal newVY = curVY + (curVY * m_factor * -1 * dt);
89
90 if (!m_threshold) {
91 if (sign(a: curVX) != sign(a: newVX))
92 newVX = 0;
93 if (sign(a: curVY) != sign(a: newVY))
94 newVY = 0;
95 } else {
96 qreal curMag = qSqrt(v: curVX*curVX + curVY*curVY);
97 if (curMag <= m_threshold + epsilon)
98 return false;
99 qreal newMag = qSqrt(v: newVX*newVX + newVY*newVY);
100 if (newMag <= m_threshold + epsilon || //went past the threshold, stop there instead
101 sign(a: curVX) != sign(a: newVX) || //went so far past maybe it came out the other side!
102 sign(a: curVY) != sign(a: newVY)) {
103 qreal theta = qAtan2(y: curVY, x: curVX);
104 newVX = m_threshold * qCos(v: theta);
105 newVY = m_threshold * qSin(v: theta);
106 }
107 }
108
109 d->setInstantaneousVX(vx: newVX, particleSystem: m_system);
110 d->setInstantaneousVY(vy: newVY, particleSystem: m_system);
111 return true;
112}
113QT_END_NAMESPACE
114
115#include "moc_qquickfriction_p.cpp"
116

source code of qtdeclarative/src/particles/qquickfriction.cpp