#include <QtGui> 
#include <QtDebug> 

class PrintThread : public QThread 
{ 
public: 
PrintThread(QObject* parent) 
: QThread(parent) 
{ 
} 

void run() 
{ 
/*forever 
{ 
QImage image(128, 128, QImage::Format_ARGB32_Premultiplied); 
image.fill(0x0); 
QPainter p(&image); 
QTextDocument document; 
document.setPlainText(QLatin1String("render this string")); 
document.drawContents(&p); 
}*/ 
qDebug()<<"thread start"; 
QImage image(128, 128, QImage::Format_ARGB32); 
image.fill(0x0); 
QPainter p(&image); 
QTextDocument document; 
document.setPlainText(QLatin1String("render this string")); 
document.drawContents(&p); 
qDebug()<<"thread finished"; 
} 
}; 

class MyWidget : public QWidget 
{ 
Q_OBJECT 
public: 
MyWidget(); 
private slots: 
void slotStart(); 
void deleteThreadLater(); 
void start10Thread(); 
private: 
QLineEdit *m_edit; 
QPushButton *m_print; 
PrintThread* m_thread; 
QTimer m_timer; 
}; 

MyWidget::MyWidget() 
:m_thread(NULL) 
{ 
QVBoxLayout* mainLayout = new QVBoxLayout(this); 
m_print = new QPushButton("Start Timer"); 
connect(m_print, SIGNAL(clicked()), this, SLOT(start10Thread())); 
connect(&m_timer, SIGNAL(timeout()), this, SLOT(slotStart())); 
m_edit = new QLineEdit; 
mainLayout->addWidget(m_print); 
mainLayout->addWidget(m_edit); 
} 
void MyWidget::slotStart() 
{ 
if(NULL == m_thread) 
{ 
m_thread = new PrintThread(this); 
connect(m_thread, SIGNAL(finished()), this, SLOT(deleteThreadLater())); 
m_edit->setText("new thread starting"); 
m_thread->start(); 
} 
} 
void MyWidget::start10Thread() 
{ 
if(!m_timer.isActive()) 
{ 
m_timer.start(2000); 
m_print->setText("Stop Timer"); 
} 
else 
{ 
m_timer.stop(); 
m_print->setText("Start Timer"); 
} 
} 
void MyWidget::deleteThreadLater() 
{ 
if(NULL != m_thread) 
{ 
delete m_thread; 
m_thread = NULL; 
m_edit->setText("thread stopped"); 
} 
} 

int main(int argc, char *argv[]) 
{ 
QApplication app(argc, argv); 
MyWidget* widget = new MyWidget(); 
widget->show(); 
return app.exec(); 
} 

#include "main.moc"

qDebug()<<"thread start"; 
		QImage image(128, 128, QImage::Format_ARGB32);
		QPainter p(&image);
		image.fill(0x0);
		QTextDocument document; 
		QPlainTextDocumentLayout *layout = new     QPlainTextDocumentLayout(&document);
		document.setDocumentLayout(layout);
		document.setPlainText(QLatin1String("render this string"));
		document.drawContents(&p); 
		delete layout;
		qDebug()<<"thread finished"; 

QAbstractTextDocumentLayout *QTextDocument::documentLayout() const
{
    Q_D(const QTextDocument);
    if (!d->lout) {
        QTextDocument *that = const_cast<QTextDocument *>(this);
        that->d_func()->setLayout(new QTextDocumentLayout(that));
    }
    return d->lout;
}