wheelwidget.cpp Example File

webkitwidgets/scroller/wheel/wheelwidget.cpp
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#include <QtWidgets>

#include "wheelwidget.h"

#define WHEEL_SCROLL_OFFSET 50000.0

AbstractWheelWidget::AbstractWheelWidget(bool touch, QWidget *parent)
    : QWidget(parent)
    , m_currentItem(0)
    , m_itemOffset(0)
{
// ![0]
    QScroller::grabGesture(this, touch ? QScroller::TouchGesture : QScroller::LeftMouseButtonGesture);
// ![0]
}

AbstractWheelWidget::~AbstractWheelWidget()
{ }

int AbstractWheelWidget::currentIndex() const
{
    return m_currentItem;
}

void AbstractWheelWidget::setCurrentIndex(int index)
{
    if (index >= 0 && index < itemCount()) {
        m_currentItem = index;
        m_itemOffset = 0;
        update();
    }
}

bool AbstractWheelWidget::event(QEvent *e)
{
    switch (e->type()) {
// ![1]
    case QEvent::ScrollPrepare:
    {
        // We set the snap positions as late as possible so that we are sure
        // we get the correct itemHeight
        QScroller *scroller = QScroller::scroller(this);
        scroller->setSnapPositionsY( WHEEL_SCROLL_OFFSET, itemHeight() );

        QScrollPrepareEvent *se = static_cast<QScrollPrepareEvent *>(e);
        se->setViewportSize(QSizeF(size()));
        // we claim a huge scrolling area and a huge content position and
        // hope that the user doesn't notice that the scroll area is restricted
        se->setContentPosRange(QRectF(0.0, 0.0, 0.0, WHEEL_SCROLL_OFFSET * 2));
        se->setContentPos(QPointF(0.0, WHEEL_SCROLL_OFFSET + m_currentItem * itemHeight() + m_itemOffset));
        se->accept();
        return true;
    }
// ![1]
// ![2]
    case QEvent::Scroll:
    {
        QScrollEvent *se = static_cast<QScrollEvent *>(e);

        qreal y = se->contentPos().y();
        int iy = y - WHEEL_SCROLL_OFFSET;
        int ih = itemHeight();

// ![2]
// ![3]
        // -- calculate the current item position and offset and redraw the widget
        int ic = itemCount();
        if (ic>0) {
            m_currentItem = iy / ih % ic;
            m_itemOffset = iy % ih;

            // take care when scrolling backwards. Modulo returns negative numbers
            if (m_itemOffset < 0) {
                m_itemOffset += ih;
                m_currentItem--;
            }

            if (m_currentItem < 0)
                m_currentItem += ic;
        }
        // -- repaint
        update();

        se->accept();
        return true;
// ![3]
    }
    default:
        return QWidget::event(e);
    }
    return true;
}

void AbstractWheelWidget::paintEvent(QPaintEvent* event)
{
    Q_UNUSED( event );

    // -- first calculate size and position.
    int w = width();
    int h = height();

    QPainter painter(this);
    QPalette palette = QApplication::palette();
    QPalette::ColorGroup colorGroup = isEnabled() ? QPalette::Active : QPalette::Disabled;

    // linear gradient brush
    QLinearGradient grad(0.5, 0, 0.5, 1.0);
    grad.setColorAt(0, palette.color(colorGroup, QPalette::ButtonText));
    grad.setColorAt(0.2, palette.color(colorGroup, QPalette::Button));
    grad.setColorAt(0.8, palette.color(colorGroup, QPalette::Button));
    grad.setColorAt(1.0, palette.color(colorGroup, QPalette::ButtonText));
    grad.setCoordinateMode( QGradient::ObjectBoundingMode );
    QBrush gBrush( grad );

    // paint a border and background
    painter.setPen(palette.color(colorGroup, QPalette::ButtonText));
    painter.setBrush(gBrush);
    // painter.setBrushOrigin( QPointF( 0.0, 0.0 ) );
    painter.drawRect( 0, 0, w-1, h-1 );

    // paint inner border
    painter.setPen(palette.color(colorGroup, QPalette::Button));
    painter.setBrush(Qt::NoBrush);
    painter.drawRect( 1, 1, w-3, h-3 );

    // paint the items
    painter.setClipRect( QRect( 3, 3, w-6, h-6 ) );
    painter.setPen(palette.color(colorGroup, QPalette::ButtonText));

    int iH = itemHeight();
    int iC = itemCount();
    if (iC > 0) {

        m_itemOffset = m_itemOffset % iH;

        for (int i=-h/2/iH; i<=h/2/iH+1; i++) {

            int itemNum = m_currentItem + i;
            while (itemNum < 0)
                itemNum += iC;
            while (itemNum >= iC)
                itemNum -= iC;

            paintItem(&painter, itemNum, QRect(6, h/2 +i*iH - m_itemOffset - iH/2, w-6, iH ));
        }
    }

    // draw a transparent bar over the center
    QColor highlight = palette.color(colorGroup, QPalette::Highlight);
    highlight.setAlpha(150);

    QLinearGradient grad2(0.5, 0, 0.5, 1.0);
    grad2.setColorAt(0, highlight);
    grad2.setColorAt(1.0, highlight.lighter());
    grad2.setCoordinateMode( QGradient::ObjectBoundingMode );
    QBrush gBrush2( grad2 );

    QLinearGradient grad3(0.5, 0, 0.5, 1.0);
    grad3.setColorAt(0, highlight);
    grad3.setColorAt(1.0, highlight.darker());
    grad3.setCoordinateMode( QGradient::ObjectBoundingMode );
    QBrush gBrush3( grad3 );

    painter.fillRect( QRect( 0, h/2 - iH/2, w, iH/2 ), gBrush2 );
    painter.fillRect( QRect( 0, h/2,        w, iH/2 ), gBrush3 );
}

/*!
    Rotates the wheel widget to a given index.
    You can also give an index greater than itemCount or less than zero in which
    case the wheel widget will scroll in the given direction and end up with
    (index % itemCount)
*/
void AbstractWheelWidget::scrollTo(int index)
{
    QScroller *scroller = QScroller::scroller(this);

    scroller->scrollTo(QPointF(0, WHEEL_SCROLL_OFFSET + index * itemHeight()), 5000);
}

/*!
    \class StringWheelWidget
    \brief The StringWheelWidget class is an implementation of the AbstractWheelWidget class that draws QStrings as items.
    \sa AbstractWheelWidget
*/

StringWheelWidget::StringWheelWidget(bool touch)
    : AbstractWheelWidget(touch)
{ }

QStringList StringWheelWidget::items() const
{
    return m_items;
}

void StringWheelWidget::setItems( const QStringList &items )
{
    m_items = items;
    if (m_currentItem >= items.count())
        m_currentItem = items.count()-1;
    update();
}

QSize StringWheelWidget::sizeHint() const
{
    // determine font size
    QFontMetrics fm(font());

    return QSize( fm.width("m") * 10 + 6, fm.height() * 7 + 6 );
}

QSize StringWheelWidget::minimumSizeHint() const
{
    QFontMetrics fm(font());

    return QSize( fm.width("m") * 5 + 6, fm.height() * 3 + 6 );
}

void StringWheelWidget::paintItem(QPainter* painter, int index, const QRect &rect)
{
    painter->drawText(rect, Qt::AlignCenter, m_items.at(index));
}

int StringWheelWidget::itemHeight() const
{
    QFontMetrics fm(font());
    return fm.height();
}

int StringWheelWidget::itemCount() const
{
    return m_items.count();
}

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