QT-解决无边框界面拖动卡屏问题(附带源码)

#ifndef DRAGSHADOW_H
#define DRAGSHADOW_H
#include <QtGui>
class DragShadow : public QWidget
{
　　Q_OBJECT
private:
　　QImage m_image;
protected:
　　bool getInvertColor(int x, int y, QColor &color);
　　void paintEvent(QPaintEvent *);
　　void showEvent( QShowEvent * event );
public:
　　explicit DragShadow(QWidget *parent = 0);
　　void setSizePos(int x, int y, int w, int h);
　　void setPos(int x,int y );
　　void setPos(QPoint pos );
signals:

public slots:

};
#endif // DRAGSHADOW_H

#include "DragShadow.h"

DragShadow::DragShadow(QWidget *parent) :
QWidget(NULL)
{
　　setWindowFlags(Qt::FramelessWindowHint|Qt::Tool);
　　setAttribute(Qt::WA_TranslucentBackground);
}

void DragShadow::setSizePos(int x, int y, int w, int h)
{
　　if(w%2==0)
　　　　w+=1;
　　if(h%2==0)
　　　　h+=1;
　　this->setGeometry(x,y,w,h);
}

void DragShadow::setPos(int x,int y )
{
　　this->move(x,y);
　　this->update();
}

void DragShadow::setPos(QPoint pos )
{
　　this->move(pos);
　　this->update();
}

void DragShadow::showEvent( QShowEvent * event )
{