Russian Qt Forum

#include <QApplication>
#include <QPainter>
#include <QImage>
#include <QMouseEvent>
#include <QPaintEvent>
#include <QWidget>


class Pa : public QWidget
{
public:
	Pa()
	{
		pixmap_ = QPixmap( 4096, 4096 );
		pixmap_.fill( 0xffffffff );
		pen_ = QPen( QBrush( Qt::black ), 5.0f );
	}

protected:
	void mousePressEvent( QMouseEvent * e )
	{
		if ( e->button() == Qt::LeftButton )
		{
			QPainter p( &pixmap_ );
			p.setPen( pen_ );
			p.drawPoint( e->pos() );
			p.end();

			lastPoint_ = e->pos();

			update();
		}
	}

	void mouseMoveEvent( QMouseEvent * e )
	{
		if ( e->buttons() & Qt::LeftButton )
		{
			QPainter p( &pixmap_ );
			p.setPen( pen_ );
			p.drawLine( lastPoint_, e->pos() );
			p.end();

			lastPoint_ = e->pos();

			update();
		}
	}

	void paintEvent( QPaintEvent * )
	{
		QPainter p( this );
		p.setCompositionMode( QPainter::CompositionMode_Source );
		p.drawPixmap( QPoint(), pixmap_ );
	}

private:
	QPen pen_;
	QPixmap pixmap_;
	QPoint lastPoint_;
};

int main( int argc, char ** argv )
{
	QApplication app( argc, argv );

	Pa pa;
	pa.show();

	return app.exec();
}