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# Hello, World

This example brings up the words "Hello, World" moving up and down, and in different colors.

Header file:

    /****************************************************************************
    ** $Id:  qt/hello.h   3.0.5   edited Oct 12 2001 $
    **
    ** Copyright (C) 1992-2000 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #ifndef HELLO_H
    #define HELLO_H

    #include <qwidget.h>

    class Hello : public QWidget
    {
        Q_OBJECT
    public:
        Hello( const char *text, QWidget *parent=0, const char *name=0 );
    signals:
        void clicked();
    protected:
        void mouseReleaseEvent( QMouseEvent * );
        void paintEvent( QPaintEvent * );
    private slots:
        void animate();
    private:
        QString t;
        int     b;
    };

    #endif

Implementation:

    /****************************************************************************
    ** $Id:  qt/hello.cpp   3.0.5   edited May 7 17:30 $
    **
    ** Copyright (C) 1992-2000 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #include "hello.h"
    #include <qpushbutton.h>
    #include <qtimer.h>
    #include <qpainter.h>
    #include <qpixmap.h>

    /*
      Constructs a Hello widget. Starts a 40 ms animation timer.
    */

    Hello::Hello( const char *text, QWidget *parent, const char *name )
        : QWidget(parent,name), t(text), b(0)
    {
        QTimer *timer = new QTimer(this);
        connect( timer, SIGNAL(timeout()), SLOT(animate()) );
        timer->start( 40 );

        resize( 260, 130 );
    }

    /*
      This private slot is called each time the timer fires.
    */

    void Hello::animate()
    {
        b = (b + 1) & 15;
        repaint( FALSE );
    }

    /*
      Handles mouse button release events for the Hello widget.

      We emit the clicked() signal when the mouse is released inside
      the widget.
    */

    void Hello::mouseReleaseEvent( QMouseEvent *e )
    {
        if ( rect().contains( e->pos() ) )
            emit clicked();
    }

    /*
      Handles paint events for the Hello widget.

      Flicker-free update. The text is first drawn in the pixmap and the
      pixmap is then blt'ed to the screen.
    */

    void Hello::paintEvent( QPaintEvent * )
    {
        static int sin_tbl[16] = {
            0, 38, 71, 92, 100, 92, 71, 38, 0, -38, -71, -92, -100, -92, -71, -38};

        if ( t.isEmpty() )
            return;

        // 1: Compute some sizes, positions etc.
        QFontMetrics fm = fontMetrics();
        int w = fm.width(t) + 20;
        int h = fm.height() * 2;
        int pmx = width()/2 - w/2;
        int pmy = height()/2 - h/2;

        // 2: Create the pixmap and fill it with the widget's background
        QPixmap pm( w, h );
        pm.fill( this, pmx, pmy );

        // 3: Paint the pixmap. Cool wave effect
        QPainter p;
        int x = 10;
        int y = h/2 + fm.descent();
        int i = 0;
        p.begin( &pm );
        p.setFont( font() );
        while ( !t[i].isNull() ) {
            int i16 = (b+i) & 15;
            p.setPen( QColor((15-i16)*16,255,255,QColor::Hsv) );
            p.drawText( x, y-sin_tbl[i16]*h/800, t.mid(i,1), 1 );
            x += fm.width( t[i] );
            i++;
        }
        p.end();

        // 4: Copy the pixmap to the Hello widget
        bitBlt( this, pmx, pmy, &pm );
    }

Main:

    /****************************************************************************
    ** $Id:  qt/main.cpp   3.0.5   edited Oct 12 2001 $
    **
    ** Copyright (C) 1992-2000 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #include "hello.h"
    #include <qapplication.h>

    /*
      The program starts here. It parses the command line and builds a message
      string to be displayed by the Hello widget.
    */

    int main( int argc, char **argv )
    {
        QApplication a(argc,argv);
        QString s;
        for ( int i=1; i<argc; i++ ) {
            s += argv[i];
            if ( i<argc-1 )
                s += " ";
        }
        if ( s.isEmpty() )
            s = "Hello, World";
        Hello h( s );
    #ifndef QT_NO_WIDGET_TOPEXTRA   // for Qt/Embedded minimal build
        h.setCaption( "Qt says hello" );
    #endif
        QObject::connect( &h, SIGNAL(clicked()), &a, SLOT(quit()) );
        h.setFont( QFont("times",32,QFont::Bold) );         // default font
        h.setBackgroundColor( Qt::white );                  // default bg color
        a.setMainWidget( &h );
        h.show();
        return a.exec();
    }

See also Examples.