14.1.336. tablet_qt/qobjects/flickcharm.cpp

/* ============================================================================
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the demos of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see http://www.qt.io/terms-conditions. For further
** information use the contact form at http://www.qt.io/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 or version 3 as published by the Free
** Software Foundation and appearing in the file LICENSE.LGPLv21 and
** LICENSE.LGPLv3 included in the packaging of this file. Please review the
** following information to ensure the GNU Lesser General Public License
** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** As a special exception, The Qt Company gives you certain additional
** rights. These rights are described in The Qt Company LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** $QT_END_LICENSE$
**
============================================================================ */

#define RNC_NO_QT_WEBKIT

#include "flickcharm.h"

#include <QAbstractScrollArea>
#include <QApplication>
#include <QBasicTimer>
#include <QDebug>
#include <QEvent>
#include <QHash>
#include <QList>
#include <QMouseEvent>
#include <QScrollBar>
#include <QTime>
#ifndef RNC_NO_QT_WEBKIT
#include <QWebFrame>
#include <QWebView>
#endif
#include "common/preprocessor_aid.h"

const int fingerAccuracyThreshold = 3;

struct FlickData {
    enum class State {
        Steady,  // Interaction without scrolling
        ManualScroll,  // Scrolling manually with the finger on the screen
        AutoScroll,  // Scrolling automatically
        AutoScrollAcceleration  // Scrolling automatically but a finger is on the screen
    };
    State state = State::Steady;
    QWidget* widget = nullptr;
    QPoint pressPos;
    QPoint lastPos;
    QPoint speed;
    QTime speedTimer;
    QList<QEvent*> ignored;
    QTime accelerationTimer;
    bool lastPosValid:1;
    bool waitingAcceleration:1;

    FlickData() :
        lastPosValid(false),
        waitingAcceleration(false)
    {}

    void resetSpeed()
    {
        speed = QPoint();
        lastPosValid = false;
    }
    void updateSpeed(const QPoint& newPosition)
    {
        if (lastPosValid) {
            const int timeElapsed = speedTimer.elapsed();
            if (timeElapsed) {
                const QPoint newPixelDiff = (newPosition - lastPos);
                const QPoint pixelsPerSecond = newPixelDiff * (1000 / timeElapsed);
                // fingers are inacurates, we ignore small changes to avoid stopping the autoscroll because
                // of a small horizontal offset when scrolling vertically
                const int newSpeedY = (qAbs(pixelsPerSecond.y()) > fingerAccuracyThreshold)
                        ? pixelsPerSecond.y() : 0;
                const int newSpeedX = (qAbs(pixelsPerSecond.x()) > fingerAccuracyThreshold)
                        ? pixelsPerSecond.x() : 0;
                if (state == State::AutoScrollAcceleration) {
                    const int max = 4000; // px by seconds
                    const int oldSpeedY = speed.y();
                    const int oldSpeedX = speed.x();

// Was this:
//                    if ((oldSpeedY <= 0 && newSpeedY <= 0) ||  (oldSpeedY >= 0 && newSpeedY >= 0)
//                            && (oldSpeedX <= 0 && newSpeedX <= 0) ||  (oldSpeedX >= 0 && newSpeedX >= 0)) {

                    if ((oldSpeedY <= 0 && newSpeedY <= 0) ||
                            ((oldSpeedY >= 0 && newSpeedY >= 0)
                             && (oldSpeedX <= 0 && newSpeedX <= 0)) ||
                            (oldSpeedX >= 0 && newSpeedX >= 0)) {
                        // RNC: this was A || B && C || D.
                        // gcc flags that up as a warning ("suggest parentheses
                        // around '&&' within '||'), very sensibly.
                        // So should it be A || (B && C) || D, or
                        // (A || B) && (C || D)?
                        // Let's assume that it was correct to start with; the
                        // C++ operator precedence is && above ||.
                        speed.setY(qBound(-max, (oldSpeedY + (newSpeedY / 4)), max));
                        speed.setX(qBound(-max, (oldSpeedX + (newSpeedX / 4)), max));
                    } else {
                        speed = QPoint();
                    }
                } else {
                    const int max = 2500; // px by seconds
                    // we average the speed to avoid strange effects with the last delta
                    if (!speed.isNull()) {
                        speed.setX(qBound(-max, (speed.x() / 4) + (newSpeedX * 3 / 4), max));
                        speed.setY(qBound(-max, (speed.y() / 4) + (newSpeedY * 3 / 4), max));
                    } else {
                        speed = QPoint(newSpeedX, newSpeedY);
                    }
                }
            }
        } else {
            lastPosValid = true;
        }
        speedTimer.start();
        lastPos = newPosition;
    }

    // scroll by dx, dy
    // return true if the widget was scrolled
    bool scrollWidget(const int dx, const int dy)
    {
        auto scrollArea = qobject_cast<QAbstractScrollArea*>(widget);
        if (scrollArea) {
            const int x = scrollArea->horizontalScrollBar()->value();
            const int y = scrollArea->verticalScrollBar()->value();
            scrollArea->horizontalScrollBar()->setValue(x - dx);
            scrollArea->verticalScrollBar()->setValue(y - dy);
            return (scrollArea->horizontalScrollBar()->value() != x
                    || scrollArea->verticalScrollBar()->value() != y);
        }

#ifndef RNC_NO_QT_WEBKIT
        QWebView* webView = qobject_cast<QWebView*>(widget);
        if (webView) {
            QWebFrame* frame = webView->page()->mainFrame();
            const QPoint position = frame->scrollPosition();
            frame->setScrollPosition(position - QPoint(dx, dy));
            return frame->scrollPosition() != position;
        }
#endif
        return false;
    }

    bool scrollTo(const QPoint& newPosition)
    {
        const QPoint delta = newPosition - lastPos;
        updateSpeed(newPosition);
        return scrollWidget(delta.x(), delta.y());
    }
};


class FlickCharmPrivate
{
public:
    QHash<QWidget*, FlickData*> flickData;
    QBasicTimer ticker;
    QTime timeCounter;
    void startTicker(QObject* object)
    {
        if (!ticker.isActive()) {
            ticker.start(15, object);
        }
        timeCounter.start();
    }
};


FlickCharm::FlickCharm(QObject* parent): QObject(parent)
{
    d = new FlickCharmPrivate;
}


FlickCharm::~FlickCharm()
{
    delete d;
}


void FlickCharm::activateOn(QWidget* widget)
{
    auto scrollArea = qobject_cast<QAbstractScrollArea*>(widget);
    if (scrollArea) {
        scrollArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
        scrollArea->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);

        QWidget* viewport = scrollArea->viewport();

        viewport->installEventFilter(this);
        scrollArea->installEventFilter(this);

        d->flickData.remove(viewport);
        d->flickData[viewport] = new FlickData;
        d->flickData[viewport]->widget = widget;
        d->flickData[viewport]->state = FlickData::State::Steady;

        return;
    }

#ifndef RNC_NO_QT_WEBKIT
    QWebView* webView = qobject_cast<QWebView*>(widget);
    if (webView) {
        QWebFrame* frame = webView->page()->mainFrame();
        frame->setScrollBarPolicy(Qt::Vertical, Qt::ScrollBarAlwaysOff);
        frame->setScrollBarPolicy(Qt::Horizontal, Qt::ScrollBarAlwaysOff);

        webView->installEventFilter(this);

        d->flickData.remove(webView);
        d->flickData[webView] = new FlickData;
        d->flickData[webView]->widget = webView;
        d->flickData[webView]->state = FlickData::Steady;

        return;
    }
#endif

    qWarning() << "FlickCharm only works on QAbstractScrollArea (and derived classes)";
#ifndef RNC_NO_QT_WEBKIT
    qWarning() << "or QWebView (and derived classes)";
#endif
}


void FlickCharm::deactivateFrom(QWidget* widget)
{
    auto scrollArea = qobject_cast<QAbstractScrollArea*>(widget);
    if (scrollArea) {
        QWidget* viewport = scrollArea->viewport();

        viewport->removeEventFilter(this);
        scrollArea->removeEventFilter(this);

        delete d->flickData[viewport];
        d->flickData.remove(viewport);

        return;
    }

#ifndef RNC_NO_QT_WEBKIT
    QWebView* webView = qobject_cast<QWebView*>(widget);
    if (webView) {
        webView->removeEventFilter(this);

        delete d->flickData[webView];
        d->flickData.remove(webView);

        return;
    }
#endif
}


static QPoint deaccelerate(const QPoint& speed, const int deltatime)
{
    const int deltaSpeed = deltatime;

    int x = speed.x();
    int y = speed.y();
    x = (x == 0) ? x : (x > 0) ? qMax(0, x - deltaSpeed) : qMin(0, x + deltaSpeed);
    y = (y == 0) ? y : (y > 0) ? qMax(0, y - deltaSpeed) : qMin(0, y + deltaSpeed);
    return QPoint(x, y);
}


bool FlickCharm::eventFilter(QObject* object, QEvent* event)
{
    if (!object->isWidgetType()) {
        return false;
    }

    const QEvent::Type type = event->type();

    switch (type) {
    case QEvent::MouseButtonPress:
    case QEvent::MouseMove:
    case QEvent::MouseButtonRelease:
        break;
    case QEvent::MouseButtonDblClick: // skip double click
        return true;
    default:
        return false;
    }

    auto mouseEvent = static_cast<QMouseEvent*>(event);
    if (type == QEvent::MouseMove && mouseEvent->buttons() != Qt::LeftButton) {
        return false;
    }

    if (mouseEvent->modifiers() != Qt::NoModifier) {
        return false;
    }

    QWidget* viewport = qobject_cast<QWidget*>(object);
    FlickData* data = d->flickData.value(viewport);
    if (!viewport || !data || data->ignored.removeAll(event)) {
        return false;
    }

    const QPoint mousePos = mouseEvent->pos();
    bool consumed = false;
    switch (data->state) {

    case FlickData::State::Steady:
        if (type == QEvent::MouseButtonPress) {
            consumed = true;
            data->pressPos = mousePos;
        } else if (type == QEvent::MouseButtonRelease) {
            consumed = true;
            auto event1 = new QMouseEvent(QEvent::MouseButtonPress,
                                          data->pressPos, Qt::LeftButton,
                                          Qt::LeftButton, Qt::NoModifier);
            auto event2 = new QMouseEvent(QEvent::MouseButtonRelease,
                                          data->pressPos, Qt::LeftButton,
                                          Qt::LeftButton, Qt::NoModifier);

            data->ignored << event1;
            data->ignored << event2;
            QApplication::postEvent(object, event1);
            QApplication::postEvent(object, event2);
        } else if (type == QEvent::MouseMove) {
            consumed = true;
            data->scrollTo(mousePos);

            const QPoint delta = mousePos - data->pressPos;
            if (delta.x() > fingerAccuracyThreshold ||
                    delta.y() > fingerAccuracyThreshold) {
                data->state = FlickData::State::ManualScroll;
            }
        }
        break;

    case FlickData::State::ManualScroll:
        if (type == QEvent::MouseMove) {
            consumed = true;
            data->scrollTo(mousePos);
        } else if (type == QEvent::MouseButtonRelease) {
            consumed = true;
            data->state = FlickData::State::AutoScroll;
            data->lastPosValid = false;
            d->startTicker(this);
        }
        break;

    case FlickData::State::AutoScroll:
        if (type == QEvent::MouseButtonPress) {
            consumed = true;
            data->state = FlickData::State::AutoScrollAcceleration;
            data->waitingAcceleration = true;
            data->accelerationTimer.start();
            data->updateSpeed(mousePos);
            data->pressPos = mousePos;
        } else if (type == QEvent::MouseButtonRelease) {
            consumed = true;
            data->state = FlickData::State::Steady;
            data->resetSpeed();
        }
        break;

    case FlickData::State::AutoScrollAcceleration:
        if (type == QEvent::MouseMove) {
            consumed = true;
            data->updateSpeed(mousePos);
            data->accelerationTimer.start();
            if (data->speed.isNull()) {
                data->state = FlickData::State::ManualScroll;
            }
        } else if (type == QEvent::MouseButtonRelease) {
            consumed = true;
            data->state = FlickData::State::AutoScroll;
            data->waitingAcceleration = false;
            data->lastPosValid = false;
        }
        break;

#ifdef COMPILER_WANTS_DEFAULT_IN_EXHAUSTIVE_SWITCH
    default:
        break;
#endif
    }
    data->lastPos = mousePos;

    // return true;  // RNC: commented out; see below

    // RNC: return value from eventFilter() is: "if you want to filter the
    // event out, i.e. stop it being handled further, return true; otherwise
    // return false.
    // The Qt implementation was "return true;", which means that "consumed" is
    // not used. Should it be "return consumed;"? Yes, think so.
    return consumed;
}


void FlickCharm::timerEvent(QTimerEvent* event)
{
    int count = 0;
    QHashIterator<QWidget*, FlickData*> item(d->flickData);
    while (item.hasNext()) {
        item.next();
        FlickData* data = item.value();
        if (data->state == FlickData::State::AutoScrollAcceleration
                && data->waitingAcceleration
                && data->accelerationTimer.elapsed() > 40) {
            data->state = FlickData::State::ManualScroll;
            data->resetSpeed();
        }
        if (data->state == FlickData::State::AutoScroll ||
                data->state == FlickData::State::AutoScrollAcceleration) {
            const int timeElapsed = d->timeCounter.elapsed();
            const QPoint delta = (data->speed) * timeElapsed / 1000;
            bool hasScrolled = data->scrollWidget(delta.x(), delta.y());

            if (data->speed.isNull() || !hasScrolled) {
                data->state = FlickData::State::Steady;
            } else {
                count++;
            }
            data->speed = deaccelerate(data->speed, timeElapsed);
        }
    }

    if (!count) {
        d->ticker.stop();
    } else {
        d->timeCounter.start();
    }

    QObject::timerEvent(event);
}