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| |
| #include "qquickfriction_p.h" |
| #include <qmath.h> |
| |
| QT_BEGIN_NAMESPACE |
| /*! |
| \qmltype Friction |
| \instantiates QQuickFrictionAffector |
| \inqmlmodule QtQuick.Particles |
| \ingroup qtquick-particles |
| \inherits Affector |
| \brief For applying friction proportional to the particle's current velocity. |
| |
| */ |
| |
| /*! |
| \qmlproperty real QtQuick.Particles::Friction::factor |
| |
| A drag will be applied to moving objects which is this factor of their current velocity. |
| */ |
| /*! |
| \qmlproperty real QtQuick.Particles::Friction::threshold |
| |
| The drag will only be applied to objects with a velocity above the threshold velocity. The |
| drag applied will bring objects down to the threshold velocity, but no further. |
| |
| The default threshold is 0 |
| */ |
| static qreal sign(qreal a) |
| { |
| return a >= 0 ? 1 : -1; |
| } |
| |
| static const qreal epsilon = 0.00001; |
| |
| QQuickFrictionAffector::QQuickFrictionAffector(QQuickItem *parent) : |
| QQuickParticleAffector(parent), m_factor(0.0), m_threshold(0.0) |
| { |
| } |
| |
| bool QQuickFrictionAffector::affectParticle(QQuickParticleData *d, qreal dt) |
| { |
| if (!m_factor) |
| return false; |
| qreal curVX = d->curVX(m_system); |
| qreal curVY = d->curVY(m_system); |
| if (!curVX && !curVY) |
| return false; |
| qreal newVX = curVX + (curVX * m_factor * -1 * dt); |
| qreal newVY = curVY + (curVY * m_factor * -1 * dt); |
| |
| if (!m_threshold) { |
| if (sign(curVX) != sign(newVX)) |
| newVX = 0; |
| if (sign(curVY) != sign(newVY)) |
| newVY = 0; |
| } else { |
| qreal curMag = qSqrt(curVX*curVX + curVY*curVY); |
| if (curMag <= m_threshold + epsilon) |
| return false; |
| qreal newMag = qSqrt(newVX*newVX + newVY*newVY); |
| if (newMag <= m_threshold + epsilon || //went past the threshold, stop there instead |
| sign(curVX) != sign(newVX) || //went so far past maybe it came out the other side! |
| sign(curVY) != sign(newVY)) { |
| qreal theta = qAtan2(curVY, curVX); |
| newVX = m_threshold * qCos(theta); |
| newVY = m_threshold * qSin(theta); |
| } |
| } |
| |
| d->setInstantaneousVX(newVX, m_system); |
| d->setInstantaneousVY(newVY, m_system); |
| return true; |
| } |
| QT_END_NAMESPACE |
| |
| #include "moc_qquickfriction_p.cpp" |