Qt: shadow around the window

Question

I can add a shadow to the widget:

QGraphicsDropShadowEffect *bodyShadow = new QGraphicsDropShadowEffect; bodyShadow->setBlurRadius(9.0); bodyShadow->setColor(QColor(0, 0, 0, 160)); bodyShadow->setOffset(4.0); ui->widget->setGraphicsEffect(bodyShadow); 

But this shadow will only be left and down. I need a shadow around the widget. How to add this?

Answer 1

You can create your own effect. I will share an implementation that works.

customshadoweffect.h

 #ifndef CUSTOMSHADOWEFFECT_H #define CUSTOMSHADOWEFFECT_H #include <QGraphicsDropShadowEffect> #include <QGraphicsEffect> class CustomShadowEffect : public QGraphicsEffect { Q_OBJECT public: explicit CustomShadowEffect(QObject *parent = 0); void draw(QPainter* painter); QRectF boundingRectFor(const QRectF& rect) const; inline void setDistance(qreal distance) { _distance = distance; updateBoundingRect(); } inline qreal distance() const { return _distance; } inline void setBlurRadius(qreal blurRadius) { _blurRadius = blurRadius; updateBoundingRect(); } inline qreal blurRadius() const { return _blurRadius; } inline void setColor(const QColor& color) { _color = color; } inline QColor color() const { return _color; } private: qreal _distance; qreal _blurRadius; QColor _color; }; #endif // CUSTOMSHADOWEFFECT_H 

customshadoweffect.cpp

 #include "customshadoweffect.h" #include <QPainter> // #include <QGraphicsEffect> CustomShadowEffect::CustomShadowEffect(QObject *parent) : QGraphicsEffect(parent), _distance(4.0f), _blurRadius(10.0f), _color(0, 0, 0, 80) { } QT_BEGIN_NAMESPACE extern Q_WIDGETS_EXPORT void qt_blurImage(QPainter *p, QImage &blurImage, qreal radius, bool quality, bool alphaOnly, int transposed = 0 ); QT_END_NAMESPACE void CustomShadowEffect::draw(QPainter* painter) { // if nothing to show outside the item, just draw source if ((blurRadius() + distance()) <= 0) { drawSource(painter); return; } PixmapPadMode mode = QGraphicsEffect::PadToEffectiveBoundingRect; QPoint offset; const QPixmap px = sourcePixmap(Qt::DeviceCoordinates, &offset, mode); // return if no source if (px.isNull()) return; // save world transform QTransform restoreTransform = painter->worldTransform(); painter->setWorldTransform(QTransform()); // Calculate size for the background image QSize szi(px.size().width() + 2 * distance(), px.size().height() + 2 * distance()); QImage tmp(szi, QImage::Format_ARGB32_Premultiplied); QPixmap scaled = px.scaled(szi); tmp.fill(0); QPainter tmpPainter(&tmp); tmpPainter.setCompositionMode(QPainter::CompositionMode_Source); tmpPainter.drawPixmap(QPointF(-distance(), -distance()), scaled); tmpPainter.end(); // blur the alpha channel QImage blurred(tmp.size(), QImage::Format_ARGB32_Premultiplied); blurred.fill(0); QPainter blurPainter(&blurred); qt_blurImage(&blurPainter, tmp, blurRadius(), false, true); blurPainter.end(); tmp = blurred; // blacken the image... tmpPainter.begin(&tmp); tmpPainter.setCompositionMode(QPainter::CompositionMode_SourceIn); tmpPainter.fillRect(tmp.rect(), color()); tmpPainter.end(); // draw the blurred shadow... painter->drawImage(offset, tmp); // draw the actual pixmap... painter->drawPixmap(offset, px, QRectF()); // restore world transform painter->setWorldTransform(restoreTransform); } QRectF CustomShadowEffect::boundingRectFor(const QRectF& rect) const { qreal delta = blurRadius() + distance(); return rect.united(rect.adjusted(-delta, -delta, delta, delta)); } 

Application (to graphic element):

 // ... CustomShadowEffect *bodyShadow = new CustomShadowEffect(); bodyShadow->setBlurRadius(20.0); bodyShadow->setDistance(6.0); bodyShadow->setColor(QColor(0, 0, 0, 80)); item->setGraphicsEffect(bodyShadow); // ... 

Application to child widget:

 //... CustomShadowEffect *bodyShadow = new CustomShadowEffect(); bodyShadow->setBlurRadius(20.0); bodyShadow->setDistance(6.0); bodyShadow->setColor(QColor(0, 0, 0, 80)); ui->widget->setAutoFillBackground(true); ui->widget->setGraphicsEffect(bodyShadow); // ... 

Result:

Answer 2

I like the mhcuervo example of how to implement a custom effect. However, fwiw, I was able to get a shadow around the child widget using your code, an offset of 0 and a large enough blur radius to spread it around the child widget. (this is using Qt 5.4).