src/kitemviews/private/kitemlistsmoothscroller.cpp

   1 /***************************************************************************
   2  *   Copyright (C) 2011 by Peter Penz <peter.penz19@gmail.com>             *
   3  *                                                                         *
   4  *   This program is free software; you can redistribute it and/or modify  *
   5  *   it under the terms of the GNU General Public License as published by  *
   6  *   the Free Software Foundation; either version 2 of the License, or     *
   7  *   (at your option) any later version.                                   *
   8  *                                                                         *
   9  *   This program is distributed in the hope that it will be useful,       *
  10  *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
  11  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
  12  *   GNU General Public License for more details.                          *
  13  *                                                                         *
  14  *   You should have received a copy of the GNU General Public License     *
  15  *   along with this program; if not, write to the                         *
  16  *   Free Software Foundation, Inc.,                                       *
  17  *   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA            *
  18  ***************************************************************************/
  19
  20 #include "kitemlistsmoothscroller.h"
  21
  22 #include <QApplication>
  23 #include <QEvent>
  24 #include <QPropertyAnimation>
  25 #include <QScrollBar>
  26 #include <QWheelEvent>
  27 #include <QStyle>
  28
  29 KItemListSmoothScroller::KItemListSmoothScroller(QScrollBar* scrollBar,
  30                                                  QObject* parent) :
  31     QObject(parent),
  32     m_scrollBarPressed(false),
  33     m_smoothScrolling(true),
  34     m_scrollBar(scrollBar),
  35     m_animation(nullptr)
  36 {
  37     m_animation = new QPropertyAnimation(this);
  38 #if QT_VERSION >= QT_VERSION_CHECK(5, 10, 0)
  39     const int animationDuration = m_scrollBar->style()->styleHint(QStyle::SH_Widget_Animation_Duration, nullptr, m_scrollBar);
  40     const bool animationEnabled = (animationDuration > 0);
  41  #else
  42     const int animationDuration = 100;
  43     const bool animationEnabled = m_scrollBar->style()->styleHint(QStyle::SH_Widget_Animate, nullptr, m_scrollBar);
  44 #endif
  45     m_animation->setDuration(animationEnabled ? animationDuration : 1);
  46     connect(m_animation, &QPropertyAnimation::stateChanged,
  47             this, &KItemListSmoothScroller::slotAnimationStateChanged);
  48
  49     m_scrollBar->installEventFilter(this);
  50 }
  51
  52 KItemListSmoothScroller::~KItemListSmoothScroller()
  53 {
  54 }
  55
  56 void KItemListSmoothScroller::setScrollBar(QScrollBar *scrollBar)
  57 {
  58     m_scrollBar = scrollBar;
  59 }
  60
  61 QScrollBar* KItemListSmoothScroller::scrollBar() const
  62 {
  63     return m_scrollBar;
  64 }
  65
  66 void KItemListSmoothScroller::setTargetObject(QObject* target)
  67 {
  68     m_animation->setTargetObject(target);
  69 }
  70
  71 QObject* KItemListSmoothScroller::targetObject() const
  72 {
  73     return m_animation->targetObject();
  74 }
  75
  76 void KItemListSmoothScroller::setPropertyName(const QByteArray& propertyName)
  77 {
  78     m_animation->setPropertyName(propertyName);
  79 }
  80
  81 QByteArray KItemListSmoothScroller::propertyName() const
  82 {
  83     return m_animation->propertyName();
  84 }
  85
  86 void KItemListSmoothScroller::scrollContentsBy(qreal distance)
  87 {
  88     QObject* target = targetObject();
  89     if (!target) {
  90         return;
  91     }
  92
  93     const QByteArray name = propertyName();
  94     const qreal currentOffset = target->property(name).toReal();
  95     if (static_cast<int>(currentOffset) == m_scrollBar->value()) {
  96         // The current offset is already synchronous to the scrollbar
  97         return;
  98     }
  99
 100     const bool animRunning = (m_animation->state() == QAbstractAnimation::Running);
 101     if (animRunning) {
 102         // Stopping a running animation means skipping the range from the current offset
 103         // until the target offset. To prevent skipping of the range the difference
 104         // is added to the new target offset.
 105         const qreal oldEndOffset = m_animation->endValue().toReal();
 106         distance += (currentOffset - oldEndOffset);
 107     }
 108
 109     const qreal endOffset = currentOffset - distance;
 110     if (m_smoothScrolling || animRunning) {
 111         qreal startOffset = currentOffset;
 112         if (animRunning) {
 113             // If the animation was running and has been interrupted by assigning a new end-offset
 114             // one frame must be added to the start-offset to keep the animation smooth. This also
 115             // assures that animation proceeds even in cases where new end-offset are triggered
 116             // within a very short timeslots.
 117             startOffset += (endOffset - currentOffset) * 1000 / (m_animation->duration() * 60);
 118             if (currentOffset < endOffset) {
 119                 startOffset = qMin(startOffset, endOffset);
 120             } else {
 121                 startOffset = qMax(startOffset, endOffset);
 122             }
 123         }
 124
 125         m_animation->stop();
 126         m_animation->setStartValue(startOffset);
 127         m_animation->setEndValue(endOffset);
 128         m_animation->setEasingCurve(animRunning ? QEasingCurve::OutQuad : QEasingCurve::InOutQuad);
 129         m_animation->start();
 130         target->setProperty(name, startOffset);
 131     } else {
 132         target->setProperty(name, endOffset);
 133     }
 134 }
 135
 136 void KItemListSmoothScroller::scrollTo(qreal position)
 137 {
 138     int newValue = position;
 139     newValue = qBound(0, newValue, m_scrollBar->maximum());
 140
 141     if (newValue != m_scrollBar->value()) {
 142         m_smoothScrolling = true;
 143         m_scrollBar->setValue(newValue);
 144     }
 145 }
 146
 147 bool KItemListSmoothScroller::requestScrollBarUpdate(int newMaximum)
 148 {
 149     if (m_animation->state() == QAbstractAnimation::Running) {
 150         if (newMaximum == m_scrollBar->maximum()) {
 151             // The value has been changed by the animation, no update
 152             // of the scrollbars is required as their target state will be
 153             // reached with the end of the animation.
 154             return false;
 155         }
 156
 157         // The maximum has been changed which indicates that the content
 158         // of the view has been changed. Stop the animation in any case and
 159         // update the scrollbars immediately.
 160         m_animation->stop();
 161     }
 162     return true;
 163 }
 164
 165 bool KItemListSmoothScroller::eventFilter(QObject* obj, QEvent* event)
 166 {
 167     Q_ASSERT(obj == m_scrollBar);
 168
 169     switch (event->type()) {
 170     case QEvent::MouseButtonPress:
 171         m_scrollBarPressed = true;
 172         m_smoothScrolling = true;
 173         break;
 174
 175     case QEvent::MouseButtonRelease:
 176         m_scrollBarPressed = false;
 177         m_smoothScrolling = false;
 178         break;
 179
 180     case QEvent::Wheel:
 181         return false; // we're the ones sending them
 182
 183     default:
 184         break;
 185     }
 186
 187     return QObject::eventFilter(obj, event);
 188 }
 189
 190 void KItemListSmoothScroller::slotAnimationStateChanged(QAbstractAnimation::State newState,
 191                                                         QAbstractAnimation::State oldState)
 192 {
 193     Q_UNUSED(oldState);
 194     if (newState == QAbstractAnimation::Stopped && m_smoothScrolling && !m_scrollBarPressed) {
 195         m_smoothScrolling = false;
 196     }
 197 }
 198
 199 void KItemListSmoothScroller::handleWheelEvent(QWheelEvent* event)
 200 {
 201     const bool previous = m_smoothScrolling;
 202
 203     m_smoothScrolling = true;
 204
 205     QWheelEvent copy = *event;
 206     QApplication::sendEvent(m_scrollBar, &copy);
 207     event->setAccepted(copy.isAccepted());
 208
 209     m_smoothScrolling = previous;
 210 }
 211