Qt窗体边框阴影的绘制

    setWindowFlags(Qt::FramelessWindowHint | Qt::WindowSystemMenuHint);
    setAttribute(Qt::WA_TranslucentBackground);
    setMouseTracking(true);
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在绘图事件中绘制边框阴影

	virtual void paintEvent(QPaintEvent *event) override;
    void drawShadow(QPainter *p);
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#include 
#include 
#include 
#include 
#define FrameWidth (8)

void flwidget::paintEvent(QPaintEvent *event)
{
    QWidget::paintEvent(event);
    QPainter p(this);
    p.setRenderHint(QPainter::Antialiasing, true);


    /*--------------------------------------------------
    *   draw client background
    *--------------------------------------------------*/
    p.save();

    QRect clientRect{FrameWidth,
                FrameWidth,
                width() - 2 * FrameWidth,
                height() - 2 * FrameWidth};
    p.fillRect(clientRect,
               QBrush(Qt::white));
    p.restore();

    /*--------------------------------------------------
    *   draw window shadow
    *--------------------------------------------------*/
    if(!isMaximized())
        drawShadow(&p);

}

void flwidget::drawShadow(QPainter *p)
{
    if(FrameWidth == 0){
        return;
    }
    p->save();
    QColor color(100, 100, 100, 30);
    for (int i = 0; i < FrameWidth; i++)
    {
        color.setAlpha(static_cast<int>(120 - qSqrt(i) * 40));
        p->setPen(color);
        p->drawRoundedRect(FrameWidth - i,
                           FrameWidth - i,
                           width() - (FrameWidth - i) * 2,
                           height() - (FrameWidth - i) * 2,
                           i,
                           i);
    }
    p->restore();
}
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效果如下图：