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