// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

#include <qglobal.h>

#include <QDebug>

#include "qpainter.h"
#include "qpixmap.h"
#include "qpixmapfilter_p.h"
#include "qvarlengtharray.h"

#include "private/qguiapplication_p.h"
#include "private/qpaintengineex_p.h"
#include "private/qpaintengine_raster_p.h"
#include "qmath.h"
#include "private/qmath_p.h"
#include "private/qdrawhelper_p.h"

#include <memory>

QT_BEGIN_NAMESPACE

class QPixmapFilterPrivate : public QObjectPrivate
{
    Q_DECLARE_PUBLIC(QPixmapFilter)
public:
    QPixmapFilter::FilterType type;
};

/*!
    \class QPixmapFilter
    \since 4.5
    \ingroup painting

    \brief The QPixmapFilter class provides the basic functionality for
    pixmap filter classes. Pixmap filter can be for example colorize or blur.

    QPixmapFilter is the base class for every pixmap filter. QPixmapFilter is
    an abstract class and cannot itself be instantiated. It provides a standard
    interface for filter processing.

    \internal
*/

/*!
    \enum QPixmapFilter::FilterType

    \internal

    This enum describes the types of filter that can be applied to pixmaps.

    \value ConvolutionFilter  A filter that is used to calculate the convolution
                              of the image with a kernel. See
                              QPixmapConvolutionFilter for more information.
    \value ColorizeFilter     A filter that is used to change the overall color
                              of an image. See QPixmapColorizeFilter for more
                              information.
    \value DropShadowFilter   A filter that is used to add a drop shadow to an
                              image. See QPixmapDropShadowFilter for more
                              information.
    \value BlurFilter         A filter that is used to blur an image using
                              a simple blur radius. See QPixmapBlurFilter
                              for more information.

    \value UserFilter   The first filter type that can be used for
                        application-specific purposes.
*/


/*!
    Constructs a default QPixmapFilter with the given \a type.

    This constructor should be used when subclassing QPixmapFilter to
    create custom user filters.

    \internal
*/
QPixmapFilter::QPixmapFilter(FilterType type, QObject *parent)
    : QObject(*new QPixmapFilterPrivate, parent)
{
    d_func()->type = type;
}



/*!
   \internal
*/
QPixmapFilter::QPixmapFilter(QPixmapFilterPrivate&d, QPixmapFilter::FilterType type, QObject *parent)
    : QObject(d, parent)
{
    d_func()->type = type;
}


/*!
    Destroys the pixmap filter.

    \internal
*/
QPixmapFilter::~QPixmapFilter()
{
}

/*!
    Returns the type of the filter. All standard pixmap filter classes
    are associated with a unique value.

    \internal
*/
QPixmapFilter::FilterType QPixmapFilter::type() const
{
    Q_D(const QPixmapFilter);
    return d->type;
}

/*!
    Returns the bounding rectangle that is affected by the pixmap
    filter if the filter is applied to the specified \a rect.

    \internal
*/
QRectF QPixmapFilter::boundingRectFor(const QRectF &rect) const
{
    return rect;
}

/*!
    \fn void QPixmapFilter::draw(QPainter *painter, const QPointF &p, const QPixmap &src, const QRectF& srcRect) const

    Uses \a painter to draw filtered result of \a src at the point
    specified by \a p. If \a srcRect is specified the it will
    be used as a source rectangle to only draw a part of the source.

    draw() will affect the area which boundingRectFor() returns.

    \internal
*/

/*!
    \class QPixmapConvolutionFilter
    \since 4.5
    \ingroup painting

    \brief The QPixmapConvolutionFilter class provides convolution
    filtering for pixmaps.

    QPixmapConvolutionFilter implements a convolution pixmap filter,
    which is applied when \l{QPixmapFilter::}{draw()} is called. A
    convolution filter lets you distort an image by setting the values
    of a matrix of qreal values called its
    \l{setConvolutionKernel()}{kernel}. The matrix's values are
    usually between -1.0 and 1.0.

    \omit
    In convolution filtering, the pixel value is calculated from the
    neighboring pixels based on the weighting convolution kernel.
    This needs explaining to be useful.
    \endomit

    Example:
    \snippet code/src_gui_image_qpixmapfilter.cpp 1

    \sa {Pixmap Filters Example}, QPixmapColorizeFilter, QPixmapDropShadowFilter


    \internal
*/

class QPixmapConvolutionFilterPrivate : public QPixmapFilterPrivate
{
public:
    QPixmapConvolutionFilterPrivate(): convolutionKernel(nullptr), kernelWidth(0), kernelHeight(0), convoluteAlpha(false) {}
    ~QPixmapConvolutionFilterPrivate() {
        delete[] convolutionKernel;
    }

    qreal *convolutionKernel;
    int kernelWidth;
    int kernelHeight;
    bool convoluteAlpha;
};


/*!
    Constructs a pixmap convolution filter.

    By default there is no convolution kernel.

    \internal
*/
QPixmapConvolutionFilter::QPixmapConvolutionFilter(QObject *parent)
    : QPixmapFilter(*new QPixmapConvolutionFilterPrivate, ConvolutionFilter, parent)
{
    Q_D(QPixmapConvolutionFilter);
    d->convoluteAlpha = true;
}

/*!
    Destructor of pixmap convolution filter.

    \internal
*/
QPixmapConvolutionFilter::~QPixmapConvolutionFilter()
{
}

/*!
     Sets convolution kernel with the given number of \a rows and \a columns.
     Values from \a kernel are copied to internal data structure.

     To preserve the intensity of the pixmap, the sum of all the
     values in the convolution kernel should add up to 1.0. A sum
     greater than 1.0 produces a lighter result and a sum less than 1.0
     produces a darker and transparent result.

    \internal
*/
void QPixmapConvolutionFilter::setConvolutionKernel(const qreal *kernel, int rows, int columns)
{
    Q_D(QPixmapConvolutionFilter);
    delete [] d->convolutionKernel;
    d->convolutionKernel = new qreal[rows * columns];
    memcpy(d->convolutionKernel, kernel, sizeof(qreal) * rows * columns);
    d->kernelWidth = columns;
    d->kernelHeight = rows;
}

/*!
    Gets the convolution kernel data.

    \internal
*/
const qreal *QPixmapConvolutionFilter::convolutionKernel() const
{
    Q_D(const QPixmapConvolutionFilter);
    return d->convolutionKernel;
}

/*!
    Gets the number of rows in the convolution kernel.

    \internal
*/
int QPixmapConvolutionFilter::rows() const
{
    Q_D(const QPixmapConvolutionFilter);
    return d->kernelHeight;
}

/*!
    Gets the number of columns in the convolution kernel.

    \internal
*/
int QPixmapConvolutionFilter::columns() const
{
    Q_D(const QPixmapConvolutionFilter);
    return d->kernelWidth;
}


/*!
    \internal
*/
QRectF QPixmapConvolutionFilter::boundingRectFor(const QRectF &rect) const
{
    Q_D(const QPixmapConvolutionFilter);
    return rect.adjusted(-d->kernelWidth / 2, -d->kernelHeight / 2, (d->kernelWidth - 1) / 2, (d->kernelHeight - 1) / 2);
}

// Convolutes the image
static void convolute(
        QImage *destImage,
        const QPointF &pos,
        const QImage &srcImage,
        const QRectF &srcRect,
        QPainter::CompositionMode mode,
        qreal *kernel,
        int kernelWidth,
        int kernelHeight )
{
    const QImage processImage = (srcImage.format() != QImage::Format_ARGB32_Premultiplied ) ?               srcImage.convertToFormat(QImage::Format_ARGB32_Premultiplied) : srcImage;
    // TODO: support also other formats directly without copying

    std::unique_ptr<int[]> fixedKernel(new int[kernelWidth * kernelHeight]);
    for(int i = 0; i < kernelWidth*kernelHeight; i++)
    {
        fixedKernel[i] = (int)(65536 * kernel[i]);
    }
    QRectF trect = srcRect.isNull() ? processImage.rect() : srcRect;
    trect.moveTo(pos);
    QRectF bounded = trect.adjusted(-kernelWidth / 2, -kernelHeight / 2, (kernelWidth - 1) / 2, (kernelHeight - 1) / 2);
    QRect rect = bounded.toAlignedRect();
    QRect targetRect = rect.intersected(destImage->rect());

    QRectF srect = srcRect.isNull() ? processImage.rect() : srcRect;
    QRectF sbounded = srect.adjusted(-kernelWidth / 2, -kernelHeight / 2, (kernelWidth - 1) / 2, (kernelHeight - 1) / 2);
    QPoint srcStartPoint = sbounded.toAlignedRect().topLeft()+(targetRect.topLeft()-rect.topLeft());

    const uint *sourceStart = (const uint*)processImage.scanLine(0);
    uint *outputStart = (uint*)destImage->scanLine(0);

    int yk = srcStartPoint.y();
    for (int y = targetRect.top(); y <= targetRect.bottom(); y++) {
        uint* output = outputStart + (destImage->bytesPerLine()/sizeof(uint))*y+targetRect.left();
        int xk = srcStartPoint.x();
        for(int x = targetRect.left(); x <= targetRect.right(); x++) {
            int r = 0;
            int g = 0;
            int b = 0;
            int a = 0;

            // some out of bounds pre-checking to avoid inner-loop ifs
            int kernely = -kernelHeight/2;
            int starty = 0;
            int endy = kernelHeight;
            if (yk+kernely+endy >= srcImage.height())
                endy = kernelHeight-((yk+kernely+endy)-srcImage.height())-1;
            if (yk+kernely < 0)
                starty = -(yk+kernely);

            int kernelx = -kernelWidth/2;
            int startx = 0;
            int endx = kernelWidth;
            if (xk+kernelx+endx >= srcImage.width())
                endx = kernelWidth-((xk+kernelx+endx)-srcImage.width())-1;
            if (xk+kernelx < 0)
                startx = -(xk+kernelx);

            for (int ys = starty; ys < endy; ys ++) {
                const uint *pix = sourceStart + (processImage.bytesPerLine()/sizeof(uint))*(yk+kernely+ys) + ((xk+kernelx+startx));
                const uint *endPix = pix+endx-startx;
                int kernelPos = ys*kernelWidth+startx;
                while (pix < endPix) {
                    int factor = fixedKernel[kernelPos++];
                    a += (((*pix) & 0xff000000)>>24) * factor;
                    r += (((*pix) & 0x00ff0000)>>16) * factor;
                    g += (((*pix) & 0x0000ff00)>>8 ) * factor;
                    b += (((*pix) & 0x000000ff)    ) * factor;
                    pix++;
                }
            }

            r = qBound((int)0, r >> 16, (int)255);
            g = qBound((int)0, g >> 16, (int)255);
            b = qBound((int)0, b >> 16, (int)255);
            a = qBound((int)0, a >> 16, (int)255);
            // composition mode checking could be moved outside of loop
            if (mode == QPainter::CompositionMode_Source) {
                uint color = (a<<24)+(r<<16)+(g<<8)+b;
                *output++ = color;
            } else {
                uint current = *output;
                uchar ca = (current&0xff000000)>>24;
                uchar cr = (current&0x00ff0000)>>16;
                uchar cg = (current&0x0000ff00)>>8;
                uchar cb = (current&0x000000ff);
                uint color =
                        (((ca*(255-a) >> 8)+a) << 24)+
                        (((cr*(255-a) >> 8)+r) << 16)+
                        (((cg*(255-a) >> 8)+g) << 8)+
                        (((cb*(255-a) >> 8)+b));
                *output++ = color;
            }
            xk++;
        }
        yk++;
    }
}

/*!
    \internal
*/
void QPixmapConvolutionFilter::draw(QPainter *painter, const QPointF &p, const QPixmap &src, const QRectF& srcRect) const
{
    Q_D(const QPixmapConvolutionFilter);
    if (!painter->isActive())
        return;

    if (d->kernelWidth<=0 || d->kernelHeight <= 0)
        return;

    if (src.isNull())
        return;

    // raster implementation

    QImage *target = nullptr;
    if (painter->paintEngine()->paintDevice()->devType() == QInternal::Image) {
        target = static_cast<QImage *>(painter->paintEngine()->paintDevice());

        QTransform mat = painter->combinedTransform();

        if (mat.type() > QTransform::TxTranslate) {
            // Disabled because of transformation...
            target = nullptr;
        } else {
            QRasterPaintEngine *pe = static_cast<QRasterPaintEngine *>(painter->paintEngine());
            if (pe->clipType() == QRasterPaintEngine::ComplexClip)
                // disabled because of complex clipping...
                target = nullptr;
            else {
                QRectF clip = pe->clipBoundingRect();
                QRectF rect = boundingRectFor(srcRect.isEmpty() ? src.rect() : srcRect);
                QTransform x = painter->deviceTransform();
                if (!clip.contains(rect.translated(x.dx() + p.x(), x.dy() + p.y()))) {
                    target = nullptr;
                }

            }
        }
    }

    if (target) {
        QTransform x = painter->deviceTransform();
        QPointF offset(x.dx(), x.dy());

        convolute(target, p+offset, src.toImage(), srcRect, QPainter::CompositionMode_SourceOver, d->convolutionKernel, d->kernelWidth, d->kernelHeight);
    } else {
        QRect srect = srcRect.isNull() ? src.rect() : srcRect.toRect();
        QRect rect = boundingRectFor(srect).toRect();
        QImage result = QImage(rect.size(), QImage::Format_ARGB32_Premultiplied);
        QPoint offset = srect.topLeft() - rect.topLeft();
        convolute(&result,
                  offset,
                  src.toImage(),
                  srect,
                  QPainter::CompositionMode_Source,
                  d->convolutionKernel,
                  d->kernelWidth,
                  d->kernelHeight);
        painter->drawImage(p - offset, result);
    }
}

/*!
    \class QPixmapBlurFilter
    \since 4.6
    \ingroup multimedia

    \brief The QPixmapBlurFilter class provides blur filtering
    for pixmaps.

    QPixmapBlurFilter implements a blur pixmap filter,
    which is applied when \l{QPixmapFilter::}{draw()} is called.

    The filter lets you specialize the radius of the blur as well
    as hints as to whether to prefer performance or quality.

    By default, the blur effect is produced by applying an exponential
    filter generated from the specified blurRadius().  Paint engines
    may override this with a custom blur that is faster on the
    underlying hardware.

    \sa {Pixmap Filters Example}, QPixmapConvolutionFilter, QPixmapDropShadowFilter

    \internal
*/

class QPixmapBlurFilterPrivate : public QPixmapFilterPrivate
{
public:
    QPixmapBlurFilterPrivate() : radius(5), hints(QGraphicsBlurEffect::PerformanceHint) {}

    qreal radius;
    QGraphicsBlurEffect::BlurHints hints;
};


/*!
    Constructs a pixmap blur filter.

    \internal
*/
QPixmapBlurFilter::QPixmapBlurFilter(QObject *parent)
    : QPixmapFilter(*new QPixmapBlurFilterPrivate, BlurFilter, parent)
{
}

/*!
    Destructor of pixmap blur filter.

    \internal
*/
QPixmapBlurFilter::~QPixmapBlurFilter()
{
}

/*!
    Sets the radius of the blur filter. Higher radius produces increased blurriness.

    \internal
*/
void QPixmapBlurFilter::setRadius(qreal radius)
{
    Q_D(QPixmapBlurFilter);
    d->radius = radius;
}

/*!
    Gets the radius of the blur filter.

    \internal
*/
qreal QPixmapBlurFilter::radius() const
{
    Q_D(const QPixmapBlurFilter);
    return d->radius;
}

/*!
    Setting the blur hints to PerformanceHint causes the implementation
    to trade off visual quality to blur the image faster.  Setting the
    blur hints to QualityHint causes the implementation to improve
    visual quality at the expense of speed.

    AnimationHint causes the implementation to optimize for animating
    the blur radius, possibly by caching blurred versions of the source
    pixmap.

    The implementation is free to ignore this value if it only has a single
    blur algorithm.

    \internal
*/
void QPixmapBlurFilter::setBlurHints(QGraphicsBlurEffect::BlurHints hints)
{
    Q_D(QPixmapBlurFilter);
    d->hints = hints;
}

/*!
    Gets the blur hints of the blur filter.

    \internal
*/
QGraphicsBlurEffect::BlurHints QPixmapBlurFilter::blurHints() const
{
    Q_D(const QPixmapBlurFilter);
    return d->hints;
}

const qreal radiusScale = qreal(2.5);

/*!
    \internal
*/
QRectF QPixmapBlurFilter::boundingRectFor(const QRectF &rect) const
{
    Q_D(const QPixmapBlurFilter);
    const qreal delta = radiusScale * d->radius + 1;
    return rect.adjusted(-delta, -delta, delta, delta);
}

Q_GUI_EXPORT extern bool qt_scaleForTransform(const QTransform &transform, qreal *scale);

Q_GUI_EXPORT extern void qt_blurImage(QPainter *p, QImage &blurImage, qreal radius, bool quality, bool alphaOnly, int transposed = 0);

/*!
    \internal
*/
void QPixmapBlurFilter::draw(QPainter *painter, const QPointF &p, const QPixmap &src, const QRectF &rect) const
{
    Q_D(const QPixmapBlurFilter);
    if (!painter->isActive())
        return;

    if (src.isNull())
        return;

    QRectF srcRect = rect;
    if (srcRect.isNull())
        srcRect = src.rect();

    if (d->radius <= 1) {
        painter->drawPixmap(srcRect.translated(p), src, srcRect);
        return;
    }

    qreal scaledRadius = radiusScale * d->radius;
    qreal scale;
    if (qt_scaleForTransform(painter->transform(), &scale))
        scaledRadius /= scale;

    QImage srcImage;

    if (srcRect == src.rect()) {
        srcImage = src.toImage();
    } else {
        QRect rect = srcRect.toAlignedRect().intersected(src.rect());
        srcImage = src.copy(rect).toImage();
    }

    QTransform transform = painter->worldTransform();
    painter->translate(p);
    qt_blurImage(painter, srcImage, scaledRadius, (d->hints & QGraphicsBlurEffect::QualityHint), false);
    painter->setWorldTransform(transform);
}

// grayscales the image to dest (could be same). If rect isn't defined
// destination image size is used to determine the dimension of grayscaling
// process.
static void grayscale(const QImage &image, QImage &dest, const QRect& rect = QRect())
{
    QRect destRect = rect;
    QRect srcRect = rect;
    if (rect.isNull()) {
        srcRect = dest.rect();
        destRect = dest.rect();
    }
    if (&image != &dest) {
        destRect.moveTo(QPoint(0, 0));
    }

    const unsigned int *data = (const unsigned int *)image.bits();
    unsigned int *outData = (unsigned int *)dest.bits();

    if (dest.size() == image.size() && image.rect() == srcRect) {
        // a bit faster loop for grayscaling everything
        int pixels = dest.width() * dest.height();
        for (int i = 0; i < pixels; ++i) {
            int val = qGray(data[i]);
            outData[i] = qRgba(val, val, val, qAlpha(data[i]));
        }
    } else {
        int yd = destRect.top();
        for (int y = srcRect.top(); y <= srcRect.bottom() && y < image.height(); y++) {
            data = (const unsigned int*)image.scanLine(y);
            outData = (unsigned int*)dest.scanLine(yd++);
            int xd = destRect.left();
            for (int x = srcRect.left(); x <= srcRect.right() && x < image.width(); x++) {
                int val = qGray(data[x]);
                outData[xd++] = qRgba(val, val, val, qAlpha(data[x]));
            }
        }
    }
}

/*!
    \class QPixmapColorizeFilter
    \since 4.5
    \ingroup painting

    \brief The QPixmapColorizeFilter class provides colorizing
    filtering for pixmaps.

    A colorize filter gives the pixmap a tint of its color(). The
    filter first grayscales the pixmap and then converts those to
    colorized values using QPainter::CompositionMode_Screen with the
    chosen color. The alpha-channel is not changed.

    Example:
    \snippet code/src_gui_image_qpixmapfilter.cpp 0

    \sa QPainter::CompositionMode

    \internal
*/
class QPixmapColorizeFilterPrivate : public QPixmapFilterPrivate
{
    Q_DECLARE_PUBLIC(QPixmapColorizeFilter)
public:
    QColor color;
    qreal strength;
    quint32 opaque : 1;
    quint32 alphaBlend : 1;
    quint32 padding : 30;
};

/*!
    Constructs an pixmap colorize filter.

    Default color value for colorizing is QColor(0, 0, 192).

    \internal
*/
QPixmapColorizeFilter::QPixmapColorizeFilter(QObject *parent)
    : QPixmapFilter(*new QPixmapColorizeFilterPrivate, ColorizeFilter, parent)
{
    Q_D(QPixmapColorizeFilter);
    d->color = QColor(0, 0, 192);
    d->strength = qreal(1);
    d->opaque = true;
    d->alphaBlend = false;
}

/*!
    \internal
*/
QPixmapColorizeFilter::~QPixmapColorizeFilter()
{
}

/*!
    Gets the color of the colorize filter.

    \internal
*/
QColor QPixmapColorizeFilter::color() const
{
    Q_D(const QPixmapColorizeFilter);
    return d->color;
}

/*!
    Sets the color of the colorize filter to the \a color specified.

    \internal
*/
void QPixmapColorizeFilter::setColor(const QColor &color)
{
    Q_D(QPixmapColorizeFilter);
    d->color = color;
}

/*!
    Gets the strength of the colorize filter, 1.0 means full colorized while
    0.0 equals to no filtering at all.

    \internal
*/
qreal QPixmapColorizeFilter::strength() const
{
    Q_D(const QPixmapColorizeFilter);
    return d->strength;
}

/*!
    Sets the strength of the colorize filter to \a strength.

    \internal
*/
void QPixmapColorizeFilter::setStrength(qreal strength)
{
    Q_D(QPixmapColorizeFilter);
    d->strength = qBound(qreal(0), strength, qreal(1));
    d->opaque = !qFuzzyIsNull(d->strength);
    d->alphaBlend = !qFuzzyIsNull(d->strength - 1);
}

/*!
    \internal
*/
void QPixmapColorizeFilter::draw(QPainter *painter, const QPointF &dest, const QPixmap &src, const QRectF &srcRect) const
{
    Q_D(const QPixmapColorizeFilter);

    if (src.isNull())
        return;

    // raster implementation

    if (!d->opaque) {
        painter->drawPixmap(dest, src, srcRect);
        return;
    }

    QImage srcImage;
    QImage destImage;

    if (srcRect.isNull()) {
        srcImage = src.toImage();
        const auto format = srcImage.hasAlphaChannel() ? QImage::Format_ARGB32_Premultiplied : QImage::Format_RGB32;
        srcImage = std::move(srcImage).convertToFormat(format);
        destImage = QImage(srcImage.size(), srcImage.format());
    } else {
        QRect rect = srcRect.toAlignedRect().intersected(src.rect());

        srcImage = src.copy(rect).toImage();
        const auto format = srcImage.hasAlphaChannel() ? QImage::Format_ARGB32_Premultiplied : QImage::Format_RGB32;
        srcImage = std::move(srcImage).convertToFormat(format);
        destImage = QImage(rect.size(), srcImage.format());
    }
    destImage.setDevicePixelRatio(src.devicePixelRatio());

    // do colorizing
    QPainter destPainter(&destImage);
    grayscale(srcImage, destImage, srcImage.rect());
    destPainter.setCompositionMode(QPainter::CompositionMode_Screen);
    destPainter.fillRect(srcImage.rect(), d->color);
    destPainter.end();

    if (d->alphaBlend) {
        // alpha blending srcImage and destImage
        QImage buffer = srcImage;
        QPainter bufPainter(&buffer);
        bufPainter.setOpacity(d->strength);
        bufPainter.drawImage(0, 0, destImage);
        bufPainter.end();
        destImage = std::move(buffer);
    }

    if (srcImage.hasAlphaChannel()) {
        Q_ASSERT(destImage.format() == QImage::Format_ARGB32_Premultiplied);
        QPainter maskPainter(&destImage);
        maskPainter.setCompositionMode(QPainter::CompositionMode_DestinationIn);
        maskPainter.drawImage(0, 0, srcImage);
    }

    painter->drawImage(dest, destImage);
}

class QPixmapDropShadowFilterPrivate : public QPixmapFilterPrivate
{
public:
    QPixmapDropShadowFilterPrivate()
        : offset(8, 8), color(63, 63, 63, 180), radius(1) {}

    QPointF offset;
    QColor color;
    qreal radius;
};

/*!
    \class QPixmapDropShadowFilter
    \since 4.5
    \ingroup painting

    \brief The QPixmapDropShadowFilter class is a convenience class
    for drawing pixmaps with drop shadows.

    The drop shadow is produced by taking a copy of the source pixmap
    and applying a color to the copy using a
    QPainter::CompositionMode_DestinationIn operation. This produces a
    homogeneously-colored pixmap which is then drawn using a
    QPixmapConvolutionFilter at an offset. The original pixmap is
    drawn on top.

    The QPixmapDropShadowFilter class provides some customization
    options to specify how the drop shadow should appear. 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 dark gray shadow, blurred with a
    radius of 1 at an offset of 8 pixels towards the lower right.

    Example:
    \snippet code/src_gui_image_qpixmapfilter.cpp 2

    \sa QPixmapColorizeFilter, QPixmapConvolutionFilter

    \internal
 */

/*!
    Constructs drop shadow filter.

    \internal
*/
QPixmapDropShadowFilter::QPixmapDropShadowFilter(QObject *parent)
    : QPixmapFilter(*new QPixmapDropShadowFilterPrivate, DropShadowFilter, parent)
{
}

/*!
    Destroys drop shadow filter.

    \internal
*/
QPixmapDropShadowFilter::~QPixmapDropShadowFilter()
{
}

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

    A smaller radius results in a sharper shadow.

    \sa color(), offset()

    \internal
*/
qreal QPixmapDropShadowFilter::blurRadius() const
{
    Q_D(const QPixmapDropShadowFilter);
    return d->radius;
}

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

    Using a smaller radius results in a sharper shadow.

    \sa setColor(), setOffset()

    \internal
*/
void QPixmapDropShadowFilter::setBlurRadius(qreal radius)
{
    Q_D(QPixmapDropShadowFilter);
    d->radius = radius;
}

/*!
    Returns the color of the drop shadow.

    \sa blurRadius(), offset()

    \internal
*/
QColor QPixmapDropShadowFilter::color() const
{
    Q_D(const QPixmapDropShadowFilter);
    return d->color;
}

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

    \sa setBlurRadius(), setOffset()

    \internal
*/
void QPixmapDropShadowFilter::setColor(const QColor &color)
{
    Q_D(QPixmapDropShadowFilter);
    d->color = color;
}

/*!
    Returns the shadow offset in pixels.

    \sa blurRadius(), color()

    \internal
*/
QPointF QPixmapDropShadowFilter::offset() const
{
    Q_D(const QPixmapDropShadowFilter);
    return d->offset;
}

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

    \sa setBlurRadius(), setColor()

    \internal
*/
void QPixmapDropShadowFilter::setOffset(const QPointF &offset)
{
    Q_D(QPixmapDropShadowFilter);
    d->offset = offset;
}

/*!
    \fn void QPixmapDropShadowFilter::setOffset(qreal dx, qreal dy)
    \overload

    Sets the shadow offset in pixels to be the displacement specified by the
    horizontal \a dx and vertical \a dy coordinates.

    \sa setBlurRadius(), setColor()

    \internal
*/

/*!
    \internal
 */
QRectF QPixmapDropShadowFilter::boundingRectFor(const QRectF &rect) const
{
    Q_D(const QPixmapDropShadowFilter);
    return rect.united(rect.translated(d->offset).adjusted(-d->radius, -d->radius, d->radius, d->radius));
}

/*!
    \internal
 */
void QPixmapDropShadowFilter::draw(QPainter *p,
                                   const QPointF &pos,
                                   const QPixmap &px,
                                   const QRectF &src) const
{
    Q_D(const QPixmapDropShadowFilter);

    if (px.isNull())
        return;

    QImage tmp(px.size(), QImage::Format_ARGB32_Premultiplied);
    tmp.setDevicePixelRatio(px.devicePixelRatio());
    tmp.fill(0);
    QPainter tmpPainter(&tmp);
    tmpPainter.setCompositionMode(QPainter::CompositionMode_Source);
    tmpPainter.drawPixmap(d->offset, px);
    tmpPainter.end();

    // blur the alpha channel
    QImage blurred(tmp.size(), QImage::Format_ARGB32_Premultiplied);
    blurred.setDevicePixelRatio(px.devicePixelRatio());
    blurred.fill(0);
    QPainter blurPainter(&blurred);
    qt_blurImage(&blurPainter, tmp, d->radius, false, true);
    blurPainter.end();

    tmp = std::move(blurred);

    // blacken the image...
    tmpPainter.begin(&tmp);
    tmpPainter.setCompositionMode(QPainter::CompositionMode_SourceIn);
    tmpPainter.fillRect(tmp.rect(), d->color);
    tmpPainter.end();

    // draw the blurred drop shadow...
    p->drawImage(pos, tmp);

    // Draw the actual pixmap...
    p->drawPixmap(pos, px, src);
}

QT_END_NAMESPACE

#include "moc_qpixmapfilter_p.cpp"