Hello, World

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

Header file:

/****************************************************************************
** $Id: qt/hello.h   3.3.7   edited Aug 31 2005 $
**
** Copyright (C) 1992-2005 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   3.3.7   edited Aug 31 2005 $
**
** Copyright (C) 1992-2005 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   3.3.7   edited Aug 31 2005 $
**
** Copyright (C) 1992-2005 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.