QWidget and xvimagesink problem!

I need some help! In qt app I have a central widget. In this central widget I have a QLabel ,and another QWidget. Now with the help of gstreamer I can get the video from my webcam and show it via the second widget. Now the problem is that I want to take a screenshot of this widget and put it on the label. But the m开发者_如何学Goethods which I used only gave a blank screen.

I tried this :

QPixmap wpix = QPixmap::grabWidget(ui->videoWidget,0,0,640,480);
ui->label->setPixmap(wpix);

and this :

QPixmap  wpix=QPixmap(ui->videoWidget->size());
wpix.fill(Qt::transparent);
ui->videoWidget->render(&wpix,QPoint(0,0),QRect(0,0,640,480),QWidget::DrawWindowBackground | QWidget::DrawChildren);

The only thing that works is to use grabWindow but here another thing:

The grabWindow() function grabs pixels from the screen, not from the window, i.e. if there >is another window partially or entirely over the one you grab, you get pixels from the >overlying window, too.

Now the grabWindow() is no use because of this effect, and the above 2 methods don't want to work!

Can someone please tell me what is the problem.Might it be the fact that I set the videoWidget to be a nativeWindow (if I don't set it my video stream would not be shown)?

Please help! If you need more info let me know! And please excuse my bad english!

#include "ksmile.h"  
#include "ui_ksmile.h"  
#include <gst/interfaces/xoverlay.h>  
#include <iostream>  

KSmile::KSmile(QWidget *parent) :QMainWindow(parent),ui(new Ui::KSmile)  
{  
    QPalette p(palette()); 
    ui->setupUi(this); 


    // Set background colour to black
    p.setColor(QPalette::Background, Qt::black);
    ui->videoWidget->setPalette(p);
    ui->videoWidget->setGeometry(0,0,640,480);
    ui->videoWidget->setAttribute(Qt::WA_NativeWindow,true);
    ui->videoWidget->show();
    ui->videoWidget->activateWindow();
    QObject::connect(&iTimer, SIGNAL(timeout()), this, SLOT(timerDone()) );
    iTimer.start(500);
}  

void KSmile::startWebCam(int argc, char *argv[])    
{     
     vs_WebCam = new VideoStream(argc,argv);   
     vs_WebCam->vs_initWebCam();   
     gst_x_overlay_set_xwindow_id(GST_X_OVERLAY(vs_WebCam->vs_getVideoSink()),ui->videoWidget->winId());     
     vs_WebCam->vs_playWebCam();     
     vs_WebCam->vs_setBrightness(0);    
     vs_WebCam->vs_setContrast(0);  
     vs_WebCam->vs_setHue(0);  
     vs_WebCam->vs_setSaturation(0);  

}  
void KSmile::timerDone()  
{  
    std::cout << "In timer done " << std::endl;   
    QPixmap  wpix=QPixmap(ui->videoWidget->size());  
     wpix.fill(Qt::transparent)  
     ui->videoWidget->render(&wpix,QPoint(0,0),QRect(0,0,640,480),QWidget::DrawWindowBackground |   QWidget::DrawChildren);    
     ui->label->setPixmap(wpix);  
    /**  
     wpix = QPixmap::grabWindow(ui->videoWidget,0,0,640,480);  
     ui->label->setPixmap(wpix); */  


}  

KSmile::~KSmile()  
{  
    delete ui;  
}