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 <KGlobalSettings>
  23 #include <QEvent>
  24 #include <QPropertyAnimation>
  25 #include <QScrollBar>
  26 #include <QWheelEvent>
  27
  28 #include <KDebug>
  29
  30 KItemListSmoothScroller::KItemListSmoothScroller(QScrollBar* scrollBar,
  31                                                  QObject* parent) :
  32     QObject(parent),
  33     m_scrollBarPressed(false),
  34     m_smoothScrolling(true),
  35     m_scrollBar(scrollBar),
  36     m_animation(0)
  37 {
  38     m_animation = new QPropertyAnimation(this);
  39     const int duration = (KGlobalSettings::graphicEffectsLevel() == KGlobalSettings::NoEffects) ? 1 : 100;
  40     m_animation->setDuration(duration);
  41     connect(m_animation, &QPropertyAnimation::stateChanged,
  42             this, &KItemListSmoothScroller::slotAnimationStateChanged);
  43
  44     m_scrollBar->installEventFilter(this);
  45 }
  46
  47 KItemListSmoothScroller::~KItemListSmoothScroller()
  48 {
  49 }
  50
  51 void KItemListSmoothScroller::setScrollBar(QScrollBar *scrollBar)
  52 {
  53     m_scrollBar = scrollBar;
  54 }
  55
  56 QScrollBar* KItemListSmoothScroller::scrollBar() const
  57 {
  58     return m_scrollBar;
  59 }
  60
  61 void KItemListSmoothScroller::setTargetObject(QObject* target)
  62 {
  63     m_animation->setTargetObject(target);
  64 }
  65
  66 QObject* KItemListSmoothScroller::targetObject() const
  67 {
  68     return m_animation->targetObject();
  69 }
  70
  71 void KItemListSmoothScroller::setPropertyName(const QByteArray& propertyName)
  72 {
  73     m_animation->setPropertyName(propertyName);
  74 }
  75
  76 QByteArray KItemListSmoothScroller::propertyName() const
  77 {
  78     return m_animation->propertyName();
  79 }
  80
  81 void KItemListSmoothScroller::scrollContentsBy(qreal distance)
  82 {
  83     QObject* target = targetObject();
  84     if (!target) {
  85         return;
  86     }
  87
  88     const QByteArray name = propertyName();
  89     const qreal currentOffset = target->property(name).toReal();
  90     if (static_cast<int>(currentOffset) == m_scrollBar->value()) {
  91         // The current offset is already synchronous to the scrollbar
  92         return;
  93     }
  94
  95     const bool animRunning = (m_animation->state() == QAbstractAnimation::Running);
  96     if (animRunning) {
  97         // Stopping a running animation means skipping the range from the current offset
  98         // until the target offset. To prevent skipping of the range the difference
  99         // is added to the new target offset.
 100         const qreal oldEndOffset = m_animation->endValue().toReal();
 101         distance += (currentOffset - oldEndOffset);
 102     }
 103
 104     const qreal endOffset = currentOffset - distance;
 105     if (m_smoothScrolling || animRunning) {
 106         qreal startOffset = currentOffset;
 107         if (animRunning) {
 108             // If the animation was running and has been interrupted by assigning a new end-offset
 109             // one frame must be added to the start-offset to keep the animation smooth. This also
 110             // assures that animation proceeds even in cases where new end-offset are triggered
 111             // within a very short timeslots.
 112             startOffset += (endOffset - currentOffset) * 1000 / (m_animation->duration() * 60);
 113             if (currentOffset < endOffset) {
 114                 startOffset = qMin(startOffset, endOffset);
 115             } else {
 116                 startOffset = qMax(startOffset, endOffset);
 117             }
 118         }
 119
 120         m_animation->stop();
 121         m_animation->setStartValue(startOffset);
 122         m_animation->setEndValue(endOffset);
 123         m_animation->setEasingCurve(animRunning ? QEasingCurve::OutQuad : QEasingCurve::InOutQuad);
 124         m_animation->start();
 125         target->setProperty(name, startOffset);
 126     } else {
 127         target->setProperty(name, endOffset);
 128     }
 129 }
 130
 131 void KItemListSmoothScroller::scrollTo(qreal position)
 132 {
 133     int newValue = position;
 134     newValue = qBound(0, newValue, m_scrollBar->maximum());
 135
 136     if (newValue != m_scrollBar->value()) {
 137         m_smoothScrolling = true;
 138         m_scrollBar->setValue(newValue);
 139     }
 140 }
 141
 142 bool KItemListSmoothScroller::requestScrollBarUpdate(int newMaximum)
 143 {
 144     if (m_animation->state() == QAbstractAnimation::Running) {
 145         if (newMaximum == m_scrollBar->maximum()) {
 146             // The value has been changed by the animation, no update
 147             // of the scrollbars is required as their target state will be
 148             // reached with the end of the animation.
 149             return false;
 150         }
 151
 152         // The maximum has been changed which indicates that the content
 153         // of the view has been changed. Stop the animation in any case and
 154         // update the scrollbars immediately.
 155         m_animation->stop();
 156     }
 157     return true;
 158 }
 159
 160 bool KItemListSmoothScroller::eventFilter(QObject* obj, QEvent* event)
 161 {
 162     Q_ASSERT(obj == m_scrollBar);
 163
 164     switch (event->type()) {
 165     case QEvent::MouseButtonPress:
 166         m_scrollBarPressed = true;
 167         m_smoothScrolling = true;
 168         break;
 169
 170     case QEvent::MouseButtonRelease:
 171         m_scrollBarPressed = false;
 172         m_smoothScrolling = false;
 173         break;
 174
 175     case QEvent::Wheel:
 176         handleWheelEvent(static_cast<QWheelEvent*>(event));
 177         break;
 178
 179     default:
 180         break;
 181     }
 182
 183     return QObject::eventFilter(obj, event);
 184 }
 185
 186 void KItemListSmoothScroller::slotAnimationStateChanged(QAbstractAnimation::State newState,
 187                                                         QAbstractAnimation::State oldState)
 188 {
 189     Q_UNUSED(oldState);
 190     if (newState == QAbstractAnimation::Stopped && m_smoothScrolling && !m_scrollBarPressed) {
 191         m_smoothScrolling = false;
 192     }
 193 }
 194
 195 void KItemListSmoothScroller::handleWheelEvent(QWheelEvent* event)
 196 {
 197     const int numDegrees = event->delta() / 8;
 198     const int numSteps = numDegrees / 15;
 199
 200     const bool previous = m_smoothScrolling;
 201
 202     m_smoothScrolling = true;
 203     const int value = m_scrollBar->value();
 204     const int pageStep = m_scrollBar->pageStep();
 205     m_scrollBar->setValue(value - numSteps * pageStep);
 206
 207     m_smoothScrolling = previous;
 208
 209     event->accept();
 210 }
 211
 212 #include "kitemlistsmoothscroller.moc"