src/kitemviews/private/kitemlistsmoothscroller.cpp

   1 /*
   2  * SPDX-FileCopyrightText: 2011 Peter Penz <peter.penz19@gmail.com>
   3  *
   4  * SPDX-License-Identifier: GPL-2.0-or-later
   5  */
   6
   7 #include "kitemlistsmoothscroller.h"
   8
   9 #include <QApplication>
  10 #include <QPropertyAnimation>
  11 #include <QScrollBar>
  12 #include <QStyle>
  13 #include <QWheelEvent>
  14
  15 KItemListSmoothScroller::KItemListSmoothScroller(QScrollBar* scrollBar,
  16                                                  QObject* parent) :
  17     QObject(parent),
  18     m_scrollBarPressed(false),
  19     m_smoothScrolling(true),
  20     m_scrollBar(scrollBar),
  21     m_animation(nullptr)
  22 {
  23     m_animation = new QPropertyAnimation(this);
  24     const int animationDuration = m_scrollBar->style()->styleHint(QStyle::SH_Widget_Animation_Duration, nullptr, m_scrollBar);
  25     const bool animationEnabled = (animationDuration > 0);
  26     m_animation->setDuration(animationEnabled ? animationDuration : 1);
  27     connect(m_animation, &QPropertyAnimation::stateChanged,
  28             this, &KItemListSmoothScroller::slotAnimationStateChanged);
  29
  30     m_scrollBar->installEventFilter(this);
  31 }
  32
  33 KItemListSmoothScroller::~KItemListSmoothScroller()
  34 {
  35 }
  36
  37 void KItemListSmoothScroller::setScrollBar(QScrollBar *scrollBar)
  38 {
  39     m_scrollBar = scrollBar;
  40 }
  41
  42 QScrollBar* KItemListSmoothScroller::scrollBar() const
  43 {
  44     return m_scrollBar;
  45 }
  46
  47 void KItemListSmoothScroller::setTargetObject(QObject* target)
  48 {
  49     m_animation->setTargetObject(target);
  50 }
  51
  52 QObject* KItemListSmoothScroller::targetObject() const
  53 {
  54     return m_animation->targetObject();
  55 }
  56
  57 void KItemListSmoothScroller::setPropertyName(const QByteArray& propertyName)
  58 {
  59     m_animation->setPropertyName(propertyName);
  60 }
  61
  62 QByteArray KItemListSmoothScroller::propertyName() const
  63 {
  64     return m_animation->propertyName();
  65 }
  66
  67 void KItemListSmoothScroller::scrollContentsBy(qreal distance)
  68 {
  69     QObject* target = targetObject();
  70     if (!target) {
  71         return;
  72     }
  73
  74     const QByteArray name = propertyName();
  75     const qreal currentOffset = target->property(name).toReal();
  76     if (static_cast<int>(currentOffset) == m_scrollBar->value()) {
  77         // The current offset is already synchronous to the scrollbar
  78         return;
  79     }
  80
  81     const bool animRunning = (m_animation->state() == QAbstractAnimation::Running);
  82     if (animRunning) {
  83         // Stopping a running animation means skipping the range from the current offset
  84         // until the target offset. To prevent skipping of the range the difference
  85         // is added to the new target offset.
  86         const qreal oldEndOffset = m_animation->endValue().toReal();
  87         distance += (currentOffset - oldEndOffset);
  88     }
  89
  90     const qreal endOffset = currentOffset - distance;
  91     if (m_smoothScrolling || animRunning) {
  92         qreal startOffset = currentOffset;
  93         if (animRunning) {
  94             // If the animation was running and has been interrupted by assigning a new end-offset
  95             // one frame must be added to the start-offset to keep the animation smooth. This also
  96             // assures that animation proceeds even in cases where new end-offset are triggered
  97             // within a very short timeslots.
  98             startOffset += (endOffset - currentOffset) * 1000 / (m_animation->duration() * 60);
  99             if (currentOffset < endOffset) {
 100                 startOffset = qMin(startOffset, endOffset);
 101             } else {
 102                 startOffset = qMax(startOffset, endOffset);
 103             }
 104         }
 105
 106         m_animation->stop();
 107         m_animation->setStartValue(startOffset);
 108         m_animation->setEndValue(endOffset);
 109         m_animation->setEasingCurve(animRunning ? QEasingCurve::OutQuad : QEasingCurve::InOutQuad);
 110         m_animation->start();
 111         target->setProperty(name, startOffset);
 112     } else {
 113         target->setProperty(name, endOffset);
 114     }
 115 }
 116
 117 void KItemListSmoothScroller::scrollTo(qreal position)
 118 {
 119     int newValue = position;
 120     newValue = qBound(0, newValue, m_scrollBar->maximum());
 121
 122     if (newValue != m_scrollBar->value()) {
 123         m_smoothScrolling = true;
 124         m_scrollBar->setValue(newValue);
 125     }
 126 }
 127
 128 bool KItemListSmoothScroller::requestScrollBarUpdate(int newMaximum)
 129 {
 130     if (m_animation->state() == QAbstractAnimation::Running) {
 131         if (newMaximum == m_scrollBar->maximum()) {
 132             // The value has been changed by the animation, no update
 133             // of the scrollbars is required as their target state will be
 134             // reached with the end of the animation.
 135             return false;
 136         }
 137
 138         // The maximum has been changed which indicates that the content
 139         // of the view has been changed. Stop the animation in any case and
 140         // update the scrollbars immediately.
 141         m_animation->stop();
 142     }
 143     return true;
 144 }
 145
 146 bool KItemListSmoothScroller::eventFilter(QObject* obj, QEvent* event)
 147 {
 148     Q_ASSERT(obj == m_scrollBar);
 149
 150     switch (event->type()) {
 151     case QEvent::MouseButtonPress:
 152         m_scrollBarPressed = true;
 153         m_smoothScrolling = true;
 154         break;
 155
 156     case QEvent::MouseButtonRelease:
 157         m_scrollBarPressed = false;
 158         m_smoothScrolling = false;
 159         break;
 160
 161     case QEvent::Wheel:
 162         return false; // we're the ones sending them
 163
 164     default:
 165         break;
 166     }
 167
 168     return QObject::eventFilter(obj, event);
 169 }
 170
 171 void KItemListSmoothScroller::slotAnimationStateChanged(QAbstractAnimation::State newState,
 172                                                         QAbstractAnimation::State oldState)
 173 {
 174     Q_UNUSED(oldState)
 175     if (newState == QAbstractAnimation::Stopped && m_smoothScrolling && !m_scrollBarPressed) {
 176         m_smoothScrolling = false;
 177     }
 178     if (newState == QAbstractAnimation::Stopped) {
 179         Q_EMIT scrollingStopped();
 180     }
 181 }
 182
 183 void KItemListSmoothScroller::handleWheelEvent(QWheelEvent* event)
 184 {
 185     const bool previous = m_smoothScrolling;
 186
 187     m_smoothScrolling = true;
 188
 189     QWheelEvent copy = *event;
 190     QApplication::sendEvent(m_scrollBar, &copy);
 191     event->setAccepted(copy.isAccepted());
 192
 193     m_smoothScrolling = previous;
 194 }
 195