path: root/src/gui/effects/qgraphicseffect.cpp

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/*!
    \class QGraphicsEffect
    \brief The QGraphicsEffect class is the base class for all graphics effects.
    \since 4.6
    \ingroup multimedia
    \ingroup graphicsview-api

    Effects alter the appearance of elements by hooking into the rendering
    pipeline and operating between the source (e.g., a QGraphicsPixmapItem),
    and the destination device (e.g., QGraphicsView's viewport). Effects can be
    disabled by calling setEnabled(); if the effect is disabled, the source is
    rendered directly.

    If you want to add a visual effect to a e.g. a QGraphicsItem, you can either use
    one of the standard effects, or create your own effect by making a subclass
    of QGraphicsEffect. The effect can then be installed on the item by calling
    QGraphicsItem::setGraphicsEffect.

    Qt provides several standard effects, including:

    \list
    \o QGraphicsGrayScaleEffect - renders the item in shades of gray
    \o QGraphicsColorizeEffect - renders the item in shades of any given color
    \o QGraphicsPixelizeEffect - pixelizes the item with any pixel size
    \o QGraphicsBlurEffect - blurs the item by a given radius
    \o QGraphicsDropShadowEffect - renders a dropshadow behind the item
    \o QGraphicsOpacityEffect - renders the item with an opacity
    \o QGrahicsShaderEffect - renders the item with a pixel shader fragment
    \endlist

    If all you want is to add an effect to an item, you should visit the
    documentation for the specific effect to learn more about how each effect
    can be used.

    If you want to create your own custom effect, you can start by creating a
    subclass of QGraphicsEffect (or any of the existing effects), and
    reimplement the virtual function draw(). This function is called whenever
    the effect needs to redraw. draw() has two arguments: the painter, and a
    pointer to the source (QGraphicsEffectSource). The source provides extra
    context information, such as a pointer to the item that is rendering the
    effect, any cached pixmap data, and the device rect bounds. See the draw()
    documentation for more details. You can also get a pointer to the current
    source by calling source().

    If your effect changes, you can call update() to request a redraw. If your
    custom effect changes the bounding rectangle of the source (e.g., a radial
    glow effect may need to apply an extra margin), you can reimplement the
    virtual boundingRectFor() function, and call updateBoundingRect() to notify
    the framework whenever this rectangle changes. The virtual
    sourceBoundingRectChanged() function is called to notify the effects that
    the source's bounding rectangle has changed (e.g., if the source is a
    QGraphicsRectItem, then if the rectangle parameters have changed).

    \sa QGraphicsItem::setGraphicsEffect(), QWidget::setGraphicsEffect(),
    QGraphicsEffectSource
*/

#include "qgraphicseffect_p.h"

#include <QtGui/qimage.h>
#include <QtGui/qpainter.h>
#include <QtCore/qrect.h>
#include <QtCore/qdebug.h>

QT_BEGIN_NAMESPACE

/*!
    \class QGraphicsEffectSource
    \brief The QGraphicsEffectSource represents the source of which a QGraphicsEffect
    is installed on.
    \since 4.6

    When a QGraphicsEffect is installed on e.g. a QGraphicsItem, this class will act as
    a wrapper around QGraphicsItem. E.g. calling update() is effectively the same as
    calling QGraphicsItem::update().

    It also provides a pixmap() function which creates a pixmap with the source
    painted into it.

    \sa QGraphicsItem::setGraphicsEffect(), QWidget::setGraphicsEffect.
*/
QGraphicsEffectSource::QGraphicsEffectSource(QGraphicsEffectSourcePrivate &dd, QObject *parent)
    : QObject(dd, parent)
{}

QGraphicsEffectSource::~QGraphicsEffectSource()
{}

/*!
    Returns the bounds of the current painter's device.

    This function is useful when you e.g. want to draw something in device coordinates
    and want to make sure the size of the pixmap is not bigger than the device's size.

    Note that calling QGraphicsEffectSource::pixmap(Qt::DeviceCoordinates) always returns
    a pixmap which is bound to the device's size.

    \sa pixmap()
*/
QRect QGraphicsEffectSource::deviceRect() const
{
    return d_func()->deviceRect();
}

/*!
    Returns the bounding rectangle of the source mapped to the \a system specified.

    \sa draw()
*/
QRectF QGraphicsEffectSource::boundingRect(Qt::CoordinateSystem system) const
{
    return d_func()->boundingRect(system);
}

/*!
    Returns a pointer to the item if this source is a QGraphicsItem;
    otherwise returns 0;

    \sa widget()
*/
const QGraphicsItem *QGraphicsEffectSource::graphicsItem() const
{
    return d_func()->graphicsItem();
}

/*!
    Returns a pointer to the widget if this source is a QWidget;
    otherwise returns 0;

    \sa graphicsItem()
*/
const QWidget *QGraphicsEffectSource::widget() const
{
    return d_func()->widget();
}

/*!
    Returns a pointer to the style options (used when drawing the source)
    if available; otherwise returns 0.

    \sa graphicsItem(), widget()
*/
const QStyleOption *QGraphicsEffectSource::styleOption() const
{
    return d_func()->styleOption();
}

/*!
    Draws the source using the \a painter specified.

    This function should only be called from QGraphicsEffect::draw().
    For example:

    \snippet doc/src/snippets/code/src_gui_effects_qgraphicseffect.cpp 0

    \sa QGraphicsEffect::draw()
*/

void QGraphicsEffectSource::draw(QPainter *painter)
{
    d_func()->draw(painter);
}

/*!
    Schedules a redraw of the source. You can call this function whenever the
    source needs to be redrawn.

    \sa QGraphicsEffect::updateBoundingRect(), QWidget::update(), QGraphicsItem::update(),
*/
void QGraphicsEffectSource::update()
{
    d_func()->update();
}

/*!
    Returns true if the source effectively is a pixmap, e.g. a QGraphicsPixmapItem.

    This function is useful for optimization purposes, e.g. there's no point in
    drawing the source in device coordinates to avoid pixmap scaling if this function
    returns true; the source pixmap will be scaled anyways.
*/
bool QGraphicsEffectSource::isPixmap() const
{
    return d_func()->isPixmap();
}

/*!
    Returns a pixmap with the source painted into it. The \a system specifies which
    coordinate system to be used for the source. The optional out parameter
    \a offset returns the offset of which the pixmap should be painted
    at using the current painter.

    Note that the returned pixmap is bound to the current painter's device
    rect when the specified \a system is Qt::DeviceCoordinates.

    \sa QGraphicsEffect::draw(), boundingRect(), deviceRect()
*/
QPixmap QGraphicsEffectSource::pixmap(Qt::CoordinateSystem system, QPoint *offset) const
{
    return d_func()->pixmap(system, offset);
}

/*!
    Constructs a new QGraphicsEffect instance.
*/
QGraphicsEffect::QGraphicsEffect(QObject *parent)
    : QObject(*new QGraphicsEffectPrivate, parent)
{
}

/*!
    \internal
*/
QGraphicsEffect::QGraphicsEffect(QGraphicsEffectPrivate &dd, QObject *parent)
    : QObject(dd, parent)
{
}

/*!
    Removes the effect from the source, and destroys the graphics effect.
*/
QGraphicsEffect::~QGraphicsEffect()
{
    Q_D(QGraphicsEffect);
    d->setGraphicsEffectSource(0);
}

/*!
    Returns the bounding rectangle for this effect (i.e., the bounding
    rectangle of the source, adjusted by any margins applied by the effect
    itself).

    \sa boundingRectFor(), updateBoundingRect()
*/
QRectF QGraphicsEffect::boundingRect() const
{
    Q_D(const QGraphicsEffect);
    if (d->source)
        return boundingRectFor(d->source->boundingRect());
    return QRectF();
}

/*!
    Returns the bounding rectangle for this effect, given the provided source
    \a rect. When writing you own custom effect, you must call
    updateBoundingRect() whenever any parameters are changed that may cause
    this this function to return a different value.

    \sa boundingRect()
*/
QRectF QGraphicsEffect::boundingRectFor(const QRectF &rect) const
{
    return rect;
}

/*!
    \property QGraphicsEffect::enabled
    \brief whether the effect is enabled or not.

    If an effect is disabled, the source will be rendered with as normal, with
    no interference from the effect. If the effect is enabled (default), the
    source will be rendered with the effect applied.

    This property is provided so that you can disable certain effects on slow
    platforms, in order to ensure that the user interface is responsive.

    \sa enabledChanged()
*/
bool QGraphicsEffect::isEnabled() const
{
    Q_D(const QGraphicsEffect);
    return d->isEnabled;
}

void QGraphicsEffect::setEnabled(bool enable)
{
    Q_D(QGraphicsEffect);
    if (d->isEnabled == enable)
        return;

    d->isEnabled = enable;
    if (d->source)
        d->source->update();
    emit enabledChanged(enable);
}

/*!
    \fn void QGraphicsEffect::enabledChanged(bool enabled)

    This signal is emitted whenever the effect is enabled or disabled.

    \sa isEnabled()
*/

/*!
    Returns a pointer to the source, which provides extra context information
    that can be useful for the effect.

    \sa draw()
*/
QGraphicsEffectSource *QGraphicsEffect::source() const
{
    Q_D(const QGraphicsEffect);
    return d->source;
}

/*!
    This function notifies the effect framework that the effect's bounding
    rectangle has changed. As a custom effect author, you must call this
    function whenever you change any parameters that will cause the virtual
    boundingRectFor() function to return a different value.

    \sa boundingRectFor(), boundingRect()
*/
void QGraphicsEffect::updateBoundingRect()
{
    Q_D(QGraphicsEffect);
    if (d->source)
        d->source->update();
}

/*!
    \fn virtual void QGraphicsEffect::draw(QPainter *painter,
    QGraphicsEffectSource *source) = 0

    This pure virtual function draws the effect and is called whenever the source()
    needs to be drawn.

    Reimplement this function in a QGraphicsEffect subclass to provide the effect's
    drawing implementation, using \a painter. The \a source parameter is provided
    for convenience; its value is the same as source(). Example:

    \snippet doc/src/snippets/code/src_gui_effects_qgraphicseffect.cpp 1

    Note that this function should not be called explicitly by the user, since it's
    meant for re-implementation purposes only.

    \sa QGraphicsEffectSource
*/

/*!
    \enum QGraphicsEffect::ChangeFlag

    This enum describes what has changed in QGraphicsEffectSource.

    \value SourceAttached The effect is installed on a source.
    \value SourceDetached The effect is uninstalled on a source.
    \value SourceBoundingRectChanged The bounding rect of the source has changed.
    \value SourceInvalidated The visual appearance of the source has changed.
*/

/*!
    This virtual function is called by QGraphicsEffect to notify the effect
    that the source has changed. If the effect applies any cache, then this
    cache must be purged in order to reflect the new appearance of the source.

    The \a flags describes what has changed.
*/
void QGraphicsEffect::sourceChanged(ChangeFlags flags)
{
    Q_UNUSED(flags);
}

/*!
    \class QGraphicsGrayscaleEffect
    \brief The QGraphicsGrayscaleEffect class provides a grayscale effect.
    \since 4.6

    A grayscale effect renders the source in shades of gray.

    \sa QGraphicsColorizeEffect
*/
QGraphicsGrayscaleEffect::QGraphicsGrayscaleEffect(QObject *parent)
    : QGraphicsEffect(*new QGraphicsGrayscaleEffectPrivate, parent)
{
}

QGraphicsGrayscaleEffect::~QGraphicsGrayscaleEffect()
{
}

void QGraphicsGrayscaleEffect::draw(QPainter *painter, QGraphicsEffectSource *source)
{
    Q_D(QGraphicsGrayscaleEffect);
    QPoint offset;
    if (source->isPixmap()) {
        // No point in drawing in device coordinates (pixmap will be scaled anyways).
        const QPixmap pixmap = source->pixmap(Qt::LogicalCoordinates, &offset);
        d->filter->draw(painter, offset, pixmap);
        return;
    }

    // Draw pixmap in device coordinates to avoid pixmap scaling;
    const QPixmap pixmap = source->pixmap(Qt::DeviceCoordinates, &offset);
    QTransform restoreTransform = painter->worldTransform();
    painter->setWorldTransform(QTransform());
    d->filter->draw(painter, offset, pixmap);
    painter->setWorldTransform(restoreTransform);

}

/*!
    \class QGraphicsColorizeEffect
    \brief The QGraphicsColorizeEffect provides a colorize effect.
    \since 4.6

    A colorize effect renders the source with a tint of its color(). The
    color can be modified using the setColor() function.

    By default, the color is light blue (QColor(0, 0, 192)).

    \sa QGraphicsGrayscaleEffect
*/
QGraphicsColorizeEffect::QGraphicsColorizeEffect(QObject *parent)
    : QGraphicsEffect(*new QGraphicsColorizeEffectPrivate, parent)
{
}

QGraphicsColorizeEffect::~QGraphicsColorizeEffect()
{
}

/*!
    Returns the color.

    \sa setColor(), colorChanged()
*/
QColor QGraphicsColorizeEffect::color() const
{
    Q_D(const QGraphicsColorizeEffect);
    return d->filter->color();
}

/*!
    Sets the color to the \a color specified.

    \sa color(), colorChanged()
*/
void QGraphicsColorizeEffect::setColor(const QColor &color)
{
    Q_D(QGraphicsColorizeEffect);
    if (d->filter->color() == color)
        return;

    d->filter->setColor(color);
    emit colorChanged(color);
}

/*!
    \fn void QGraphicsColorizeEffect::colorChanged(const QColor &color)

    This signal is emitted whenever the effect's color changes.
*/

void QGraphicsColorizeEffect::draw(QPainter *painter, QGraphicsEffectSource *source)
{
    Q_D(QGraphicsColorizeEffect);
    QPoint offset;
    if (source->isPixmap()) {
        // No point in drawing in device coordinates (pixmap will be scaled anyways).
        const QPixmap pixmap = source->pixmap(Qt::LogicalCoordinates, &offset);
        d->filter->draw(painter, offset, pixmap);
        return;
    }

    // Draw pixmap in deviceCoordinates to avoid pixmap scaling.
    const QPixmap pixmap = source->pixmap(Qt::DeviceCoordinates, &offset);
    QTransform restoreTransform = painter->worldTransform();
    painter->setWorldTransform(QTransform());
    d->filter->draw(painter, offset, pixmap);
    painter->setWorldTransform(restoreTransform);
}

/*!
    \class QGraphicsPixelizeEffect
    \brief The QGraphicsPixelizeEffect provides a pixelize effect.
    \since 4.6

    A pixelize effect renders the source in lower resolution. This effect
    is useful for reducing details, in e.g. a censorship. The resolution
    can be modified using the setPixelSize() function.

    By default, the pixel size is 3.

    \sa QGraphicsBlurEffect
*/
QGraphicsPixelizeEffect::QGraphicsPixelizeEffect(QObject *parent)
    : QGraphicsEffect(*new QGraphicsPixelizeEffectPrivate, parent)
{
}

QGraphicsPixelizeEffect::~QGraphicsPixelizeEffect()
{
}

/*!
    Returns the size of a pixel.

    \sa setPixelSize(), pixelSizeChanged()
*/
int QGraphicsPixelizeEffect::pixelSize() const
{
    Q_D(const QGraphicsPixelizeEffect);
    return d->pixelSize;
}

/*!
    Sets the size of a pixel to the \a size specified.

    Setting the \a size to e.g. 2 means two pixels in the source will
    be used to represent one pixel. Using a bigger size results in
    lower resolution.

    \sa pixelSize(), pixelSizeChanged()
*/
void QGraphicsPixelizeEffect::setPixelSize(int size)
{
    Q_D(QGraphicsPixelizeEffect);
    if (d->pixelSize == size)
        return;

    d->pixelSize = size;
    emit pixelSizeChanged(size);
}

/*!
    \fn void QGraphicsPixelizeEffect::pixelSizeChanged(int size)

    This signal is emitted whenever the effect's pixel size changes.
*/

static inline void pixelize(QImage *image, int pixelSize)
{
    Q_ASSERT(pixelSize > 0);
    Q_ASSERT(image);
    int width = image->width();
    int height = image->height();
    for (int y = 0; y < height; y += pixelSize) {
        int ys = qMin(height - 1, y + pixelSize / 2);
        QRgb *sbuf = reinterpret_cast<QRgb*>(image->scanLine(ys));
        for (int x = 0; x < width; x += pixelSize) {
            int xs = qMin(width - 1, x + pixelSize / 2);
            QRgb color = sbuf[xs];
            for (int yi = 0; yi < qMin(pixelSize, height - y); ++yi) {
                QRgb *buf = reinterpret_cast<QRgb*>(image->scanLine(y + yi));
                for (int xi = 0; xi < qMin(pixelSize, width - x); ++xi)
                    buf[x + xi] = color;
            }
        }
    }
}

void QGraphicsPixelizeEffect::draw(QPainter *painter, QGraphicsEffectSource *source)
{
    Q_D(QGraphicsPixelizeEffect);
    if (d->pixelSize <= 0) {
        source->draw(painter);
        return;
    }

    QPoint offset;
    if (source->isPixmap()) {
        const QPixmap pixmap = source->pixmap(Qt::LogicalCoordinates, &offset);
        QImage image = pixmap.toImage().convertToFormat(QImage::Format_ARGB32);
        pixelize(&image, d->pixelSize);
        painter->drawImage(offset, image);
        return;
    }

    // Draw pixmap in device coordinates to avoid pixmap scaling.
    const QPixmap pixmap = source->pixmap(Qt::DeviceCoordinates, &offset);

    // pixelize routine
    QImage image = pixmap.toImage().convertToFormat(QImage::Format_ARGB32);
    pixelize(&image, d->pixelSize);

    QTransform restoreTransform = painter->worldTransform();
    painter->setWorldTransform(QTransform());
    painter->drawImage(offset, image);
    painter->setWorldTransform(restoreTransform);
}

/*!
    \class QGraphicsBlurEffect
    \brief The QGraphicsBlurEffect provides a blur effect.
    \since 4.6

    A blur effect blurs the source. This effect is useful for reducing details,
    e.g. when the source loses focus and you want to draw attention to other
    elements. The level of detail can be modified using the setBlurRadius()
    function.

    By default, the blur radius is 5 pixels.

    \sa QGraphicsPixelizeEffect
*/
QGraphicsBlurEffect::QGraphicsBlurEffect(QObject *parent)
    : QGraphicsEffect(*new QGraphicsBlurEffectPrivate, parent)
{
}

QGraphicsBlurEffect::~QGraphicsBlurEffect()
{
}

/*!
    Returns the blur radius.

    \sa setBlurRadius(), blurRadiusChanged()
*/
int QGraphicsBlurEffect::blurRadius() const
{
    Q_D(const QGraphicsBlurEffect);
    return d->filter->radius();
}

/*!
    Sets the blur radius to the \a radius specified.

    Using a smaller radius results in a sharper appearance, whereas a
    bigger radius results in a more blurry appearance.

    \sa blurRadius(), blurRadiusChanged()
*/
void QGraphicsBlurEffect::setBlurRadius(int radius)
{
    Q_D(QGraphicsBlurEffect);
    if (d->filter->radius() == radius)
        return;

    d->filter->setRadius(radius);
    updateBoundingRect();
    emit blurRadiusChanged(radius);
}

/*!
    \fn void QGraphicsBlurEffect::blurRadiusChanged(int radius)

    This signal is emitted whenever the effect's blur radius changes.
*/

QRectF QGraphicsBlurEffect::boundingRectFor(const QRectF &rect) const
{
    Q_D(const QGraphicsBlurEffect);
    return d->filter->boundingRectFor(rect);
}

void QGraphicsBlurEffect::draw(QPainter *painter, QGraphicsEffectSource *source)
{
    Q_D(QGraphicsBlurEffect);
    if (d->filter->radius() <= 0) {
        source->draw(painter);
        return;
    }

    QPoint offset;
    if (source->isPixmap()) {
        // No point in drawing in device coordinates (pixmap will be scaled anyways).
        const QPixmap pixmap = source->pixmap(Qt::LogicalCoordinates, &offset);
        d->filter->draw(painter, offset, pixmap);
        return;
    }

    // Draw pixmap in device coordinates to avoid pixmap scaling.
    const QPixmap pixmap = source->pixmap(Qt::DeviceCoordinates, &offset);
    QTransform restoreTransform = painter->worldTransform();
    painter->setWorldTransform(QTransform());
    d->filter->draw(painter, offset, pixmap);
    painter->setWorldTransform(restoreTransform);
}

/*!
    \class QGraphicsDropShadowEffect
    \brief The QGraphicsDropShadowEffect class provides a drop shadow effect.
    \since 4.6

    A drop shadow effect renders the source with a drop shadow. The color of
    the drop shadow can be modified using the setColor() function, the drop
    shadow offset can be modified using the setOffset function, and the blur
    radius of the drop shadow can be changed through the setBlurRadius()
    function.

    By default, the drop shadow is a semi-transparent dark gray
    (QColor(63, 63, 63, 180)) shadow, blurred with a radius of 1 at an
    offset of 8 pixels towards the lower right.
*/
QGraphicsDropShadowEffect::QGraphicsDropShadowEffect(QObject *parent)
    : QGraphicsEffect(*new QGraphicsDropShadowEffectPrivate, parent)
{
}

QGraphicsDropShadowEffect::~QGraphicsDropShadowEffect()
{
}

/*!
    Returns the shadow offset in pixels.

    \sa setOffset(), blurRadius(), color(), offsetChanged()
*/
QPointF QGraphicsDropShadowEffect::offset() const
{
    Q_D(const QGraphicsDropShadowEffect);
    return d->filter->offset();
}

/*!
    Sets the shadow offset in pixels to the \a offset specified.

    \sa offset(), setBlurRadius(), setColor(), offsetChanged()
*/
void QGraphicsDropShadowEffect::setOffset(const QPointF &offset)
{
    Q_D(QGraphicsDropShadowEffect);
    if (d->filter->offset() == offset)
        return;

    d->filter->setOffset(offset);
    updateBoundingRect();
    emit offsetChanged(offset);
}

/*!
    \fn void QGraphicsDropShadowEffect::offsetChanged(const QPoint &offset)

    This signal is emitted whenever the effect's shadow offset changes.
*/

/*!
    Returns the radius in pixels of the blur on the drop shadow.

    \sa setBlurRadius(), color(), offset(), blurRadiusChanged()
*/
int QGraphicsDropShadowEffect::blurRadius() const
{
    Q_D(const QGraphicsDropShadowEffect);
    return d->filter->blurRadius();
}

/*!
    Sets the radius in pixels of the blur on the drop shadow to the
    \a blurRadius specified.

    Using a smaller radius results in a sharper shadow, whereas using
    a bigger radius results in a more blurry shadow.

    \sa blurRadius(), setColor(), setOffset(), blurRadiusChanged()
*/
void QGraphicsDropShadowEffect::setBlurRadius(int blurRadius)
{
    Q_D(QGraphicsDropShadowEffect);
    if (d->filter->blurRadius() == blurRadius)
        return;

    d->filter->setBlurRadius(blurRadius);
    updateBoundingRect();
    emit blurRadiusChanged(blurRadius);
}

/*!
    \fn void QGraphicsDropShadowEffect::blurRadiusChanged(int blurRadius)

    This signal is emitted whenever the effect's blur radius changes.
*/

/*!
    Returns the color of the drop shadow.

    \sa setColor, offset(), blurRadius(), colorChanged()
*/
QColor QGraphicsDropShadowEffect::color() const
{
    Q_D(const QGraphicsDropShadowEffect);
    return d->filter->color();
}

/*!
    Sets the color of the drop shadow to the \a color specified.

    \sa color(), setOffset(), setBlurRadius(), colorChanged()
*/
void QGraphicsDropShadowEffect::setColor(const QColor &color)
{
    Q_D(QGraphicsDropShadowEffect);
    if (d->filter->color() == color)
        return;

    d->filter->setColor(color);
    emit colorChanged(color);
}

/*!
    \fn void QGraphicsDropShadowEffect::colorChanged(const QColor &color)

    This signal is emitted whenever the effect's color changes.
*/

QRectF QGraphicsDropShadowEffect::boundingRectFor(const QRectF &rect) const
{
    Q_D(const QGraphicsDropShadowEffect);
    return d->filter->boundingRectFor(rect);
}

void QGraphicsDropShadowEffect::draw(QPainter *painter, QGraphicsEffectSource *source)
{
    Q_D(QGraphicsDropShadowEffect);
    if (d->filter->blurRadius() <= 0 && d->filter->offset().isNull()) {
        source->draw(painter);
        return;
    }

    QPoint offset;
    if (source->isPixmap()) {
        // No point in drawing in device coordinates (pixmap will be scaled anyways).
        const QPixmap pixmap = source->pixmap(Qt::LogicalCoordinates, &offset);
        d->filter->draw(painter, offset, pixmap);
        return;
    }

    // Draw pixmap in device coordinates to avoid pixmap scaling.
    const QPixmap pixmap = source->pixmap(Qt::DeviceCoordinates, &offset);
    QTransform restoreTransform = painter->worldTransform();
    painter->setWorldTransform(QTransform());
    d->filter->draw(painter, offset, pixmap);
    painter->setWorldTransform(restoreTransform);
}

/*!
    \class QGraphicsOpacityEffect
    \brief The QGraphicsOpacityEffect class provides an opacity effect.
    \since 4.6

    An opacity effects renders the source with an opacity. This effect is useful
    for making the source semi-transparent, in e.g. a fade-in/fade-out sequence.
    The opacity can be modified using the setOpacity() function.

    By default, the opacity is 0.7.
*/
QGraphicsOpacityEffect::QGraphicsOpacityEffect(QObject *parent)
    : QGraphicsEffect(*new QGraphicsOpacityEffectPrivate, parent)
{
}

QGraphicsOpacityEffect::~QGraphicsOpacityEffect()
{
}

/*!
    Returns the opacity.

    \sa setOpacity(), opacityChanged()
*/
qreal QGraphicsOpacityEffect::opacity() const
{
    Q_D(const QGraphicsOpacityEffect);
    return d->opacity;
}

/*!
    Sets the opacity to the \a opacity specified. The value should be in
    the range 0.0 to 1.0, where 0.0 is fully transparent and 1.0 is
    fully opaque.

    \sa opacity(), opacityChanged()
*/
void QGraphicsOpacityEffect::setOpacity(qreal opacity)
{
    Q_D(QGraphicsOpacityEffect);
    opacity = qBound(qreal(0.0), opacity, qreal(1.0));

    if (qFuzzyCompare(d->opacity, opacity))
        return;

    d->opacity = opacity;
    emit opacityChanged(opacity);
}

/*!
    \fn void QGraphicsOpacityEffect::opacityChanged(qreal opacity)

    This signal is emitted whenever the effect's opacity changes.
*/

void QGraphicsOpacityEffect::draw(QPainter *painter, QGraphicsEffectSource *source)
{
    Q_D(QGraphicsOpacityEffect);

    // Transparent; nothing to draw.
    if (qFuzzyIsNull(d->opacity))
        return;

    // Opaque; draw directly without going through a pixmap.
    if (qFuzzyIsNull(d->opacity - 1)) {
        source->draw(painter);
        return;
    }

    painter->save();
    painter->setOpacity(d->opacity);

    QPoint offset;
    if (source->isPixmap()) {
        // No point in drawing in device coordinates (pixmap will be scaled anyways).
        const QPixmap pixmap = source->pixmap(Qt::LogicalCoordinates, &offset);
        painter->drawPixmap(offset, pixmap);
    } else {
        // Draw pixmap in device coordinates to avoid pixmap scaling;
        const QPixmap pixmap = source->pixmap(Qt::DeviceCoordinates, &offset);
        painter->setWorldTransform(QTransform());
        painter->drawPixmap(offset, pixmap);
    }

    painter->restore();
}

QT_END_NAMESPACE