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 <QEvent>
  23 #include <QPropertyAnimation>
  24 #include <QScrollBar>
  25 #include <QWheelEvent>
  26 #include <QStyle>
  27
  28 KItemListSmoothScroller::KItemListSmoothScroller(QScrollBar* scrollBar,
  29                                                  QObject* parent) :
  30     QObject(parent),
  31     m_scrollBarPressed(false),
  32     m_smoothScrolling(true),
  33     m_scrollBar(scrollBar),
  34     m_animation(0)
  35 {
  36     m_animation = new QPropertyAnimation(this);
  37     const int duration = m_scrollBar->style()->styleHint(QStyle::SH_Widget_Animate, nullptr, m_scrollBar) ? 100 : 1;
  38     m_animation->setDuration(duration);
  39     connect(m_animation, &QPropertyAnimation::stateChanged,
  40             this, &KItemListSmoothScroller::slotAnimationStateChanged);
  41
  42     m_scrollBar->installEventFilter(this);
  43 }
  44
  45 KItemListSmoothScroller::~KItemListSmoothScroller()
  46 {
  47 }
  48
  49 void KItemListSmoothScroller::setScrollBar(QScrollBar *scrollBar)
  50 {
  51     m_scrollBar = scrollBar;
  52 }
  53
  54 QScrollBar* KItemListSmoothScroller::scrollBar() const
  55 {
  56     return m_scrollBar;
  57 }
  58
  59 void KItemListSmoothScroller::setTargetObject(QObject* target)
  60 {
  61     m_animation->setTargetObject(target);
  62 }
  63
  64 QObject* KItemListSmoothScroller::targetObject() const
  65 {
  66     return m_animation->targetObject();
  67 }
  68
  69 void KItemListSmoothScroller::setPropertyName(const QByteArray& propertyName)
  70 {
  71     m_animation->setPropertyName(propertyName);
  72 }
  73
  74 QByteArray KItemListSmoothScroller::propertyName() const
  75 {
  76     return m_animation->propertyName();
  77 }
  78
  79 void KItemListSmoothScroller::scrollContentsBy(qreal distance)
  80 {
  81     QObject* target = targetObject();
  82     if (!target) {
  83         return;
  84     }
  85
  86     const QByteArray name = propertyName();
  87     const qreal currentOffset = target->property(name).toReal();
  88     if (static_cast<int>(currentOffset) == m_scrollBar->value()) {
  89         // The current offset is already synchronous to the scrollbar
  90         return;
  91     }
  92
  93     const bool animRunning = (m_animation->state() == QAbstractAnimation::Running);
  94     if (animRunning) {
  95         // Stopping a running animation means skipping the range from the current offset
  96         // until the target offset. To prevent skipping of the range the difference
  97         // is added to the new target offset.
  98         const qreal oldEndOffset = m_animation->endValue().toReal();
  99         distance += (currentOffset - oldEndOffset);
 100     }
 101
 102     const qreal endOffset = currentOffset - distance;
 103     if (m_smoothScrolling || animRunning) {
 104         qreal startOffset = currentOffset;
 105         if (animRunning) {
 106             // If the animation was running and has been interrupted by assigning a new end-offset
 107             // one frame must be added to the start-offset to keep the animation smooth. This also
 108             // assures that animation proceeds even in cases where new end-offset are triggered
 109             // within a very short timeslots.
 110             startOffset += (endOffset - currentOffset) * 1000 / (m_animation->duration() * 60);
 111             if (currentOffset < endOffset) {
 112                 startOffset = qMin(startOffset, endOffset);
 113             } else {
 114                 startOffset = qMax(startOffset, endOffset);
 115             }
 116         }
 117
 118         m_animation->stop();
 119         m_animation->setStartValue(startOffset);
 120         m_animation->setEndValue(endOffset);
 121         m_animation->setEasingCurve(animRunning ? QEasingCurve::OutQuad : QEasingCurve::InOutQuad);
 122         m_animation->start();
 123         target->setProperty(name, startOffset);
 124     } else {
 125         target->setProperty(name, endOffset);
 126     }
 127 }
 128
 129 void KItemListSmoothScroller::scrollTo(qreal position)
 130 {
 131     int newValue = position;
 132     newValue = qBound(0, newValue, m_scrollBar->maximum());
 133
 134     if (newValue != m_scrollBar->value()) {
 135         m_smoothScrolling = true;
 136         m_scrollBar->setValue(newValue);
 137     }
 138 }
 139
 140 bool KItemListSmoothScroller::requestScrollBarUpdate(int newMaximum)
 141 {
 142     if (m_animation->state() == QAbstractAnimation::Running) {
 143         if (newMaximum == m_scrollBar->maximum()) {
 144             // The value has been changed by the animation, no update
 145             // of the scrollbars is required as their target state will be
 146             // reached with the end of the animation.
 147             return false;
 148         }
 149
 150         // The maximum has been changed which indicates that the content
 151         // of the view has been changed. Stop the animation in any case and
 152         // update the scrollbars immediately.
 153         m_animation->stop();
 154     }
 155     return true;
 156 }
 157
 158 bool KItemListSmoothScroller::eventFilter(QObject* obj, QEvent* event)
 159 {
 160     Q_ASSERT(obj == m_scrollBar);
 161
 162     switch (event->type()) {
 163     case QEvent::MouseButtonPress:
 164         m_scrollBarPressed = true;
 165         m_smoothScrolling = true;
 166         break;
 167
 168     case QEvent::MouseButtonRelease:
 169         m_scrollBarPressed = false;
 170         m_smoothScrolling = false;
 171         break;
 172
 173     case QEvent::Wheel:
 174         handleWheelEvent(static_cast<QWheelEvent*>(event));
 175         return true; // eat event so that QScrollBar does not scroll one step more by itself
 176
 177     default:
 178         break;
 179     }
 180
 181     return QObject::eventFilter(obj, event);
 182 }
 183
 184 void KItemListSmoothScroller::slotAnimationStateChanged(QAbstractAnimation::State newState,
 185                                                         QAbstractAnimation::State oldState)
 186 {
 187     Q_UNUSED(oldState);
 188     if (newState == QAbstractAnimation::Stopped && m_smoothScrolling && !m_scrollBarPressed) {
 189         m_smoothScrolling = false;
 190     }
 191 }
 192
 193 void KItemListSmoothScroller::handleWheelEvent(QWheelEvent* event)
 194 {
 195     const bool previous = m_smoothScrolling;
 196
 197     m_smoothScrolling = true;
 198     int numPixels;
 199     if (!event->pixelDelta().isNull()) {
 200         numPixels = event->pixelDelta().y();
 201     } else {
 202         const int numDegrees = event->angleDelta().y() / 8;
 203         const int numSteps = numDegrees / 15;
 204         numPixels = numSteps * m_scrollBar->pageStep() / 4;
 205     }
 206     int value = m_scrollBar->value();
 207     if (event->modifiers().testFlag(Qt::ShiftModifier)) {
 208         const int scrollingDirection = numPixels > 0 ? 1 : -1;
 209         value -= m_scrollBar->pageStep() * scrollingDirection;
 210     } else {
 211         value -= numPixels;
 212     }
 213     m_scrollBar->setValue(value);
 214
 215     m_smoothScrolling = previous;
 216
 217     event->accept();
 218 }
 219