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目录

官方解析

QGraphicsEffect::draw(QPainter *painter)

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

博主例子

自己写的很有趣的小例子，程序运行截图如下：

源码如下：

blureffect.h

#ifndef BLUREFFECT_H#define BLUREFFECT_H#include 
   
    #include 
    
     QT_BEGIN_NAMESPACEclass QGraphicsItem;QT_END_NAMESPACEclass BlurEffect : public QGraphicsBlurEffect{public:    BlurEffect(QGraphicsItem *item);    void setBaseLine(const qreal y);    void setGraphicsItemSize(const QSize size);    void draw(QPainter *painter)Q_DECL_OVERRIDE;private:    void adjustForItem();    qreal m_baseLine;    QGraphicsItem *m_item;    QSize m_size;};#endif // BLUREFFECT_H
    
   

widget.h

#ifndef WIDGET_H#define WIDGET_H#include 
   
    class BlurEffect;QT_BEGIN_NAMESPACEclass QGraphicsPixmapItem;QT_END_NAMESPACEnamespace Ui {class Widget;}class Widget : public QWidget{    Q_OBJECTpublic:    explicit Widget(QWidget *parent = 0);    ~Widget();public slots:    void timeout();private:    Ui::Widget *ui;    BlurEffect *m_blurEffect;    QGraphicsPixmapItem *m_item;};#endif // WIDGET_H
   

blureffect.cpp

#include "blureffect.h"#include 
   
    #include 
    
     #include 
     
      #include 
      
       BlurEffect::BlurEffect(QGraphicsItem *item):    QGraphicsBlurEffect(),    m_baseLine(200),    m_item(item){}void BlurEffect::setBaseLine(const qreal y){    m_baseLine=y;}void BlurEffect::setGraphicsItemSize(const QSize size){    m_size=size;}void BlurEffect::draw(QPainter *painter){    adjustForItem();    painter->save();    QPen pen(QColor(abs((int)m_baseLine%256),abs((int)m_baseLine%256),abs((int)m_baseLine%256)));    pen.setWidth(3);    painter->setPen(pen);    painter->drawRect(0,0,m_size.width(),m_size.height());    painter->restore();    QGraphicsBlurEffect::draw(painter);}void BlurEffect::adjustForItem(){    qreal y=m_baseLine-m_item->scenePos().y();    qreal radius=qBound(qreal(0.0),y/32,qreal(16.0));    setBlurRadius(radius);}
      
     
    
   

main.cpp

#include "widget.h"#include 
   
    int main(int argc, char *argv[]){    QApplication a(argc, argv);    Widget w;    w.show();    return a.exec();}
   

widget.cpp

#include "widget.h"#include "ui_widget.h"#include "blureffect.h"#include 
   
    #include 
    
     #include 
     
      #include 
      
       Widget::Widget(QWidget *parent) :    QWidget(parent),    ui(new Ui::Widget){    ui->setupUi(this);    this->setWindowTitle("CSDN IT1995");    ui->graphicsView->setScene(new QGraphicsScene);    m_item=new QGraphicsPixmapItem;    m_item->setPixmap(QPixmap(":/src.jpg"));    ui->graphicsView->scene()->addItem(m_item);    m_item->setFlags(QGraphicsItem::ItemIsMovable|QGraphicsItem::ItemIsSelectable);    m_blurEffect=new BlurEffect(m_item);    m_blurEffect->setGraphicsItemSize(m_item->boundingRect().size().toSize());    m_item->setGraphicsEffect(m_blurEffect);    QTimer *timer=new QTimer(this);    connect(timer,SIGNAL(timeout()),this,SLOT(timeout()));    timer->start(500);}Widget::~Widget(){    delete ui;}void Widget::timeout(){    m_blurEffect->setBaseLine(m_item->scenePos().x()+m_item->scenePos().y());}
      
     
    
   

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