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# Show Image

This example reads and displays an image in any supported image format (GIF, BMP, PPM, XMP, etc.).

Header file:

    /****************************************************************************
    ** $Id: qt/showimg.h   3.3.5   edited Aug 31 12:17 $
    **
    ** 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 SHOWIMG_H
    #define SHOWIMG_H

    #include <qwidget.h>
    #include <qimage.h>

    class QLabel;
    class QMenuBar;
    class QPopupMenu;

    class ImageViewer : public QWidget
    {
        Q_OBJECT
    public:
        ImageViewer( QWidget *parent=0, const char *name=0, int wFlags=0 );
        ~ImageViewer();
        bool        loadImage( const QString& );
    protected:
        void        paintEvent( QPaintEvent * );
        void        resizeEvent( QResizeEvent * );
        void        mousePressEvent( QMouseEvent * );
        void        mouseReleaseEvent( QMouseEvent * );
        void        mouseMoveEvent( QMouseEvent * );

    private:
        void        scale();
        int         conversion_flags;
        bool        smooth() const;
        bool        useColorContext() const;
        int         alloc_context;
        bool        convertEvent( QMouseEvent* e, int& x, int& y );
        QString     filename;
        QImage      image;                  // the loaded image
        QPixmap     pm;                     // the converted pixmap
        QPixmap     pmScaled;               // the scaled pixmap

        QMenuBar   *menubar;
        QPopupMenu  *file;
        QPopupMenu   *saveimage;
        QPopupMenu   *savepixmap;
        QPopupMenu  *edit;
        QPopupMenu  *options;

        QWidget    *helpmsg;
        QLabel     *status;
        int         si, sp, ac, co, mo, fd, bd, // Menu item ids
                    td, ta, ba, fa, au, ad, dd,
                    ss, cc, t1, t8, t32;
        void        updateStatus();
        void        setMenuItemFlags();
        bool        reconvertImage();
        int         pickx, picky;
        int         clickx, clicky;
        bool        may_be_other;
        static ImageViewer* other;
        void        setImage(const QImage& newimage);

    private slots:
        void        to1Bit();
        void        to8Bit();
        void        to32Bit();
        void        toBitDepth(int);

        void        copy();
        void        paste();

        void        hFlip();
        void        vFlip();
        void        rot180();

        void        editText();

        void        newWindow();
        void        openFile();
        void        saveImage(int);
        void        savePixmap(int);
        void        giveHelp();
        void        doOption(int);
        void        copyFrom(ImageViewer*);
    };

    #endif // SHOWIMG_H

Implementation:

    /****************************************************************************
    ** $Id: qt/showimg.cpp   3.3.5   edited Aug 31 12:13 $
    **
    ** 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 "showimg.h"
    #include "imagetexteditor.h"
    #include <qmenubar.h>
    #include <qfiledialog.h>
    #include <qmessagebox.h>
    #include <qpopupmenu.h>
    #include <qlabel.h>
    #include <qpainter.h>
    #include <qapplication.h>
    #include <qclipboard.h>

    /*
      In the constructor, we just pass the standard parameters on to
      QWidget.

      The menu uses a single slot to simplify the process of adding
      more items to the options menu.
    */
    ImageViewer::ImageViewer( QWidget *parent, const char *name, int wFlags )
        : QWidget( parent, name, wFlags ),
          conversion_flags( PreferDither ),
          helpmsg( 0 )
    {
        pickx = -1;
        picky = -1;
        clickx = -1;
        clicky = -1;
        alloc_context = 0;

        menubar = new QMenuBar(this);
        menubar->setSeparator( QMenuBar::InWindowsStyle );

        QStrList fmt = QImage::outputFormats();
        saveimage = new QPopupMenu( menubar );
        savepixmap = new QPopupMenu( menubar );
        for (const char* f = fmt.first(); f; f = fmt.next()) {
            saveimage->insertItem( f );
            savepixmap->insertItem( f );
        }
        connect( saveimage, SIGNAL(activated(int)), this, SLOT(saveImage(int)) );
        connect( savepixmap, SIGNAL(activated(int)), this, SLOT(savePixmap(int)) );

        file = new QPopupMenu( menubar );
        menubar->insertItem( "&File", file );
        file->insertItem( "&New window", this,  SLOT(newWindow()), CTRL+Key_N );
        file->insertItem( "&Open...", this,  SLOT(openFile()), CTRL+Key_O );
        si = file->insertItem( "Save image", saveimage );
        sp = file->insertItem( "Save pixmap", savepixmap );
        file->insertSeparator();
        file->insertItem( "E&xit", qApp,  SLOT(quit()), CTRL+Key_Q );

        edit =  new QPopupMenu( menubar );
        menubar->insertItem( "&Edit", edit );
        edit->insertItem("&Copy", this, SLOT(copy()), CTRL+Key_C);
        edit->insertItem("&Paste", this, SLOT(paste()), CTRL+Key_V);
        edit->insertSeparator();
        edit->insertItem("&Horizontal flip", this, SLOT(hFlip()), ALT+Key_H);
        edit->insertItem("&Vertical flip", this, SLOT(vFlip()), ALT+Key_V);
        edit->insertItem("&Rotate 180", this, SLOT(rot180()), ALT+Key_R);
        edit->insertSeparator();
        edit->insertItem("&Text...", this, SLOT(editText()));
        edit->insertSeparator();
        t1 = edit->insertItem( "Convert to &1 bit", this, SLOT(to1Bit()) );
        t8 = edit->insertItem( "Convert to &8 bit", this, SLOT(to8Bit()) );
        t32 = edit->insertItem( "Convert to &32 bit", this, SLOT(to32Bit()) );

        options =  new QPopupMenu( menubar );
        menubar->insertItem( "&Options", options );
        ac = options->insertItem( "AutoColor" );
        co = options->insertItem( "ColorOnly" );
        mo = options->insertItem( "MonoOnly" );
        options->insertSeparator();
        fd = options->insertItem( "DiffuseDither" );
        bd = options->insertItem( "OrderedDither" );
        td = options->insertItem( "ThresholdDither" );
        options->insertSeparator();
        ta = options->insertItem( "ThresholdAlphaDither" );
        ba = options->insertItem( "OrderedAlphaDither" );
        fa = options->insertItem( "DiffuseAlphaDither" );
        options->insertSeparator();
        ad = options->insertItem( "PreferDither" );
        dd = options->insertItem( "AvoidDither" );
        options->insertSeparator();
        ss = options->insertItem( "Smooth scaling" );
        cc = options->insertItem( "Use color context" );
        if ( QApplication::colorSpec() == QApplication::ManyColor )
            options->setItemEnabled( cc, FALSE );
        options->setCheckable( TRUE );
        setMenuItemFlags();

        menubar->insertSeparator();

        QPopupMenu* help = new QPopupMenu( menubar );
        menubar->insertItem( "&Help", help );
        help->insertItem( "Help!", this, SLOT(giveHelp()), CTRL+Key_H );

        connect( options, SIGNAL(activated(int)), this, SLOT(doOption(int)) );

        status = new QLabel(this);
        status->setFrameStyle( QFrame::WinPanel | QFrame::Sunken );
        status->setFixedHeight( fontMetrics().height() + 4 );

        setMouseTracking( TRUE );
    }

    ImageViewer::~ImageViewer()
    {
        if ( alloc_context )
            QColor::destroyAllocContext( alloc_context );
        if ( other == this )
            other = 0;
    }

    /*
      This function modifies the conversion_flags when an options menu item
      is selected, then ensures all menu items are up to date, and reconverts
      the image if possibly necessary.
    */
    void ImageViewer::doOption(int item)
    {
        if ( item == ss || item == cc ) {
            // Toggle
            bool newbool = !options->isItemChecked(item);
            options->setItemChecked(item, newbool);
            // And reconvert...
            reconvertImage();
            repaint(image.hasAlphaBuffer());        // show image in widget
            return;
        }

        if ( options->isItemChecked( item ) ) return; // They are all radio buttons

        int ocf = conversion_flags;

        if ( item == ac ) {
            conversion_flags = ( conversion_flags & ~ColorMode_Mask ) | AutoColor;
        } else if ( item == co ) {
            conversion_flags = ( conversion_flags & ~ColorMode_Mask ) | ColorOnly;
        } else if ( item == mo ) {
            conversion_flags = ( conversion_flags & ~ColorMode_Mask ) | MonoOnly;
        } else if ( item == fd ) {
            conversion_flags = ( conversion_flags & ~Dither_Mask ) | DiffuseDither;
        } else if ( item == bd ) {
            conversion_flags = ( conversion_flags & ~Dither_Mask ) | OrderedDither;
        } else if ( item == td ) {
            conversion_flags = ( conversion_flags & ~Dither_Mask ) | ThresholdDither;
        } else if ( item == ta ) {
            conversion_flags = ( conversion_flags & ~AlphaDither_Mask ) | ThresholdAlphaDither;
        } else if ( item == fa ) {
            conversion_flags = ( conversion_flags & ~AlphaDither_Mask ) | DiffuseAlphaDither;
        } else if ( item == ba ) {
            conversion_flags = ( conversion_flags & ~AlphaDither_Mask ) | OrderedAlphaDither;
        } else if ( item == ad ) {
            conversion_flags = ( conversion_flags & ~DitherMode_Mask ) | PreferDither;
        } else if ( item == dd ) {
            conversion_flags = ( conversion_flags & ~DitherMode_Mask ) | AvoidDither;
        }

        if ( ocf != conversion_flags ) {
            setMenuItemFlags();
            // And reconvert...
            reconvertImage();
            repaint(image.hasAlphaBuffer());        // show image in widget
        }
    }

    /*
      Set the options menu to reflect the conversion_flags value.
    */
    void ImageViewer::setMenuItemFlags()
    {
        // File
        bool valid_image = pm.size() != QSize( 0, 0 );
        file->setItemEnabled( si, valid_image );
        file->setItemEnabled( sp, valid_image );

        // Edit
        edit->setItemEnabled( t1, image.depth() != 1 );
        edit->setItemEnabled( t8, image.depth() != 8 );
        edit->setItemEnabled( t32, image.depth() != 32 );

        // Options
        bool may_need_color_dithering =
                !valid_image
            || image.depth() == 32 && QPixmap::defaultDepth() < 24;
        bool may_need_dithering = may_need_color_dithering
             || image.depth() > 1 && options->isItemChecked(mo)
             || image.depth() > 1 && QPixmap::defaultDepth() == 1;
        bool has_alpha_mask = !valid_image || image.hasAlphaBuffer();

        options->setItemEnabled( fd, may_need_dithering );
        options->setItemEnabled( bd, may_need_dithering );
        options->setItemEnabled( td, may_need_dithering );

        options->setItemEnabled( ta, has_alpha_mask );
        options->setItemEnabled( fa, has_alpha_mask );
        options->setItemEnabled( ba, has_alpha_mask );

        options->setItemEnabled( ad, may_need_color_dithering );
        options->setItemEnabled( dd, may_need_color_dithering );

        options->setItemChecked( ac, (conversion_flags & ColorMode_Mask) == AutoColor );
        options->setItemChecked( co, (conversion_flags & ColorMode_Mask) == ColorOnly );
        options->setItemChecked( mo, (conversion_flags & ColorMode_Mask) == MonoOnly );
        options->setItemChecked( fd, (conversion_flags & Dither_Mask) == DiffuseDither );
        options->setItemChecked( bd, (conversion_flags & Dither_Mask) == OrderedDither );
        options->setItemChecked( td, (conversion_flags & Dither_Mask) == ThresholdDither );
        options->setItemChecked( ta, (conversion_flags & AlphaDither_Mask) == ThresholdAlphaDither );
        options->setItemChecked( fa, (conversion_flags & AlphaDither_Mask) == DiffuseAlphaDither );
        options->setItemChecked( ba, (conversion_flags & AlphaDither_Mask) == OrderedAlphaDither );
        options->setItemChecked( ad, (conversion_flags & DitherMode_Mask) == PreferDither );
        options->setItemChecked( dd, (conversion_flags & DitherMode_Mask) == AvoidDither );
    }

    void ImageViewer::updateStatus()
    {
        if ( pm.size() == QSize( 0, 0 ) ) {
            if ( !filename.isEmpty() )
                status->setText("Could not load image");
            else
                status->setText("No image - select Open from File menu.");
        } else {
            QString message, moremsg;
            message.sprintf("%dx%d", image.width(), image.height());
            if ( pm.size() != pmScaled.size() ) {
                moremsg.sprintf(" [%dx%d]", pmScaled.width(),
                    pmScaled.height());
                message += moremsg;
            }
            moremsg.sprintf(", %d bits ", image.depth());
            message += moremsg;
            if (image.valid(pickx,picky)) {
                moremsg.sprintf("(%d,%d)=#%0*x ",
                              pickx, picky,
                              image.hasAlphaBuffer() ? 8 : 6,
                              image.pixel(pickx,picky));
                message += moremsg;
            }
            if ( image.numColors() > 0 ) {
                if (image.valid(pickx,picky)) {
                    moremsg.sprintf(", %d/%d colors", image.pixelIndex(pickx,picky),
                        image.numColors());
                } else {
                    moremsg.sprintf(", %d colors", image.numColors());
                }
                message += moremsg;
            }
            if ( image.hasAlphaBuffer() ) {
                if ( image.depth() == 8 ) {
                    int i;
                    bool alpha[256];
                    int nalpha=0;

                    for (i=0; i<256; i++)
                        alpha[i] = FALSE;

                    for (i=0; i<image.numColors(); i++) {
                        int alevel = image.color(i) >> 24;
                        if (!alpha[alevel]) {
                            alpha[alevel] = TRUE;
                            nalpha++;
                        }
                    }
                    moremsg.sprintf(", %d alpha levels", nalpha);
                } else {
                    // Too many pixels to bother counting.
                    moremsg = ", 8-bit alpha channel";
                }
                message += moremsg;
            }
            status->setText(message);
        }
    }

    /*
      This function saves the image.
    */
    void ImageViewer::saveImage( int item )
    {
        const char* fmt = saveimage->text(item);
        QString savefilename = QFileDialog::getSaveFileName(QString::null, QString::null,
                                            this, filename);
        if ( !savefilename.isEmpty() )
            if ( !image.save( savefilename, fmt ) )
                QMessageBox::warning( this, "Save failed", "Error saving file" );
    }

    /*
      This function saves the converted image.
    */
    void ImageViewer::savePixmap( int item )
    {
        const char* fmt = savepixmap->text(item);
        QString savefilename = QFileDialog::getSaveFileName(QString::null,
                                            QString::null, this, filename);
        if ( !savefilename.isEmpty() )
            if ( !pmScaled.save( savefilename, fmt ) )
                QMessageBox::warning( this, "Save failed", "Error saving file" );
    }

    void ImageViewer::newWindow()
    {
        ImageViewer* that = new ImageViewer(0, "new window", WDestructiveClose);
        that->options->setItemChecked( that->cc, useColorContext() );
        that->show();
    }

    /*
      This function is the slot for processing the Open menu item.
    */
    void ImageViewer::openFile()
    {
        QString newfilename = QFileDialog::getOpenFileName( QString::null,
                                                            QString::null,
                                                            this );
        if ( !newfilename.isEmpty() ) {
            loadImage( newfilename ) ;
            repaint();                      // show image in widget
        }
    }

    /*
      This function loads an image from a file and resizes the widget to
      exactly fit the image size. If the file was not found or the image
      format was unknown it will resize the widget to fit the errorText
      message (see above) displayed in the current font.

      Returns TRUE if the image was successfully loaded.
    */

    bool ImageViewer::loadImage( const QString& fileName )
    {
        filename = fileName;
        bool ok = FALSE;
        if ( !filename.isEmpty() ) {
            QApplication::setOverrideCursor( waitCursor ); // this might take time
            ok = image.load(filename, 0);
            pickx = -1;
            clickx = -1;
            if ( ok )
                ok = reconvertImage();
            if ( ok ) {
                setCaption( filename );                     // set window caption
                int w = pm.width();
                int h = pm.height();

                const int reasonable_width = 128;
                if ( w < reasonable_width ) {
                    // Integer scale up to something reasonable
                    int multiply = ( reasonable_width + w - 1 ) / w;
                    w *= multiply;
                    h *= multiply;
                }

                h += menubar->heightForWidth(w) + status->height();
                resize( w, h );                             // we resize to fit image
            } else {
                pm.resize(0,0);                             // couldn't load image
                update();
            }
            QApplication::restoreOverrideCursor();  // restore original cursor
        }
        updateStatus();
        setMenuItemFlags();
        return ok;
    }

    bool ImageViewer::reconvertImage()
    {
        bool success = FALSE;

        if ( image.isNull() ) return FALSE;

        if ( alloc_context ) {
            QColor::destroyAllocContext( alloc_context );
            alloc_context = 0;
        }
        if ( useColorContext() ) {
            alloc_context = QColor::enterAllocContext();
            // Clear the image to hide flickering palette
            QPainter painter(this);
            painter.eraseRect(0, menubar->heightForWidth( width() ), width(), height());
        }

        QApplication::setOverrideCursor( waitCursor ); // this might take time
        if ( pm.convertFromImage(image, conversion_flags) )
        {
            pmScaled = QPixmap();
            scale();
            resize( width(), height() );
            success = TRUE;                         // load successful
        } else {
            pm.resize(0,0);                         // couldn't load image
        }
        updateStatus();
        setMenuItemFlags();
        QApplication::restoreOverrideCursor();      // restore original cursor

        if ( useColorContext() )
            QColor::leaveAllocContext();

        return success;                             // TRUE if loaded OK
    }

    bool ImageViewer::smooth() const
    {
        return options->isItemChecked(ss);
    }

    bool ImageViewer::useColorContext() const
    {
        return options->isItemChecked(cc);
    }

    /*
      This functions scales the pixmap in the member variable "pm" to fit the
      widget size and  puts the resulting pixmap in the member variable "pmScaled".
    */

    void ImageViewer::scale()
    {
        int h = height() - menubar->heightForWidth( width() ) - status->height();

        if ( image.isNull() ) return;

        QApplication::setOverrideCursor( waitCursor ); // this might take time
        if ( width() == pm.width() && h == pm.height() )
        {                                           // no need to scale if widget
            pmScaled = pm;                          // size equals pixmap size
        } else {
            if (smooth()) {
                pmScaled.convertFromImage(image.smoothScale(width(), h),
                    conversion_flags);
            } else {
                QWMatrix m;                         // transformation matrix
                m.scale(((double)width())/pm.width(),// define scale factors
                        ((double)h)/pm.height());
                pmScaled = pm.xForm( m );           // create scaled pixmap
            }
        }
        QApplication::restoreOverrideCursor();      // restore original cursor
    }

    /*
      The resize event handler, if a valid pixmap was loaded it will call
      scale() to fit the pixmap to the new widget size.
    */

    void ImageViewer::resizeEvent( QResizeEvent * )
    {
        status->setGeometry(0, height() - status->height(),
                            width(), status->height());

        if ( pm.size() == QSize( 0, 0 ) )           // we couldn't load the image
            return;

        int h = height() - menubar->heightForWidth( width() ) - status->height();
        if ( width() != pmScaled.width() || h != pmScaled.height())
        {                                           // if new size,
            scale();                                // scale pmScaled to window
            updateStatus();
        }
        if ( image.hasAlphaBuffer() )
            erase();
    }

    bool ImageViewer::convertEvent( QMouseEvent* e, int& x, int& y)
    {
        if ( pm.size() != QSize( 0, 0 ) ) {
            int h = height() - menubar->heightForWidth( width() ) - status->height();
            int nx = e->x() * image.width() / width();
            int ny = (e->y()-menubar->heightForWidth( width() )) * image.height() / h;
            if (nx != x || ny != y ) {
                x = nx;
                y = ny;
                updateStatus();
                return TRUE;
            }
        }
        return FALSE;
    }

    void ImageViewer::mousePressEvent( QMouseEvent *e )
    {
        may_be_other = convertEvent(e, clickx, clicky);
    }

    void ImageViewer::mouseReleaseEvent( QMouseEvent * )
    {
        if ( may_be_other )
            other = this;
    }

    /*
      Record the pixel position of interest.
    */
    void ImageViewer::mouseMoveEvent( QMouseEvent *e )
    {
        if (convertEvent(e,pickx,picky)) {
            updateStatus();
            if ((e->state()&LeftButton)) {
                may_be_other = FALSE;
                if ( clickx >= 0 && other) {
                    copyFrom(other);
                }
            }
        }
    }

    /*
      Draws the portion of the scaled pixmap that needs to be updated or prints
      an error message if no legal pixmap has been loaded.
    */

    void ImageViewer::paintEvent( QPaintEvent *e )
    {
        if ( pm.size() != QSize( 0, 0 ) ) {         // is an image loaded?
            QPainter painter(this);
            painter.setClipRect(e->rect());
            painter.drawPixmap(0, menubar->heightForWidth( width() ), pmScaled);
        }
    }

    /*
      Explain anything that might be confusing.
    */
    void ImageViewer::giveHelp()
    {
        if (!helpmsg) {
            QString helptext =
                "<b>Usage:</b> <tt>showimg [-m] <i>filename ...</i></tt>"
                "<blockquote>"
                    "<tt>-m</tt> - use <i>ManyColor</i> color spec"
                "</blockquote>"
                "<p>Supported input formats:"
                "<blockquote>";
            helptext += QImage::inputFormatList().join(", ");
            helptext += "</blockquote>";

            helpmsg = new QMessageBox( "Help", helptext,
                QMessageBox::Information, QMessageBox::Ok, 0, 0, 0, 0, FALSE );
        }
        helpmsg->show();
        helpmsg->raise();
    }

    void ImageViewer::copyFrom(ImageViewer* s)
    {
        if ( clickx >= 0 ) {
            int dx = clickx;
            int dy = clicky;
            int sx = s->clickx;
            int sy = s->clicky;
            int sw = QABS(clickx - pickx)+1;
            int sh = QABS(clicky - picky)+1;
            if ( clickx > pickx ) {
                dx = pickx;
                sx -= sw-1;
            }
            if ( clicky > picky ) {
                dy = picky;
                sy -= sh-1;
            }
            bitBlt( &image, dx, dy, &s->image, sx, sy, sw, sh );
            reconvertImage();
            repaint( image.hasAlphaBuffer() );
        }
    }
    ImageViewer* ImageViewer::other = 0;

    void ImageViewer::hFlip()
    {
        setImage(image.mirror(TRUE,FALSE));
    }

    void ImageViewer::vFlip()
    {
        setImage(image.mirror(FALSE,TRUE));
    }

    void ImageViewer::rot180()
    {
        setImage(image.mirror(TRUE,TRUE));
    }

    void ImageViewer::copy()
    {
    #ifndef QT_NO_MIMECLIPBOARD
        QApplication::clipboard()->setImage(image); // Less information loss
    #endif
    }

    void ImageViewer::paste()
    {
    #ifndef QT_NO_MIMECLIPBOARD
        QImage p = QApplication::clipboard()->image();
        if ( !p.isNull() ) {
            filename = "pasted";
            setImage(p);
        }
    #endif
    }

    void ImageViewer::setImage(const QImage& newimage)
    {
        image = newimage;

        pickx = -1;
        clickx = -1;
        setCaption( filename );                     // set window caption
        int w = image.width();
        int h = image.height();
        if ( !w )
            return;

        const int reasonable_width = 128;
        if ( w < reasonable_width ) {
            // Integer scale up to something reasonable
            int multiply = ( reasonable_width + w - 1 ) / w;
            w *= multiply;
            h *= multiply;
        }

        h += menubar->heightForWidth(w) + status->height();
        resize( w, h );                             // we resize to fit image

        reconvertImage();
        repaint( image.hasAlphaBuffer() );

        updateStatus();
        setMenuItemFlags();
    }

    void ImageViewer::editText()
    {
        ImageTextEditor editor(image,this);
        editor.exec();
    }

    void ImageViewer::to1Bit()
    {
        toBitDepth(1);
    }

    void ImageViewer::to8Bit()
    {
        toBitDepth(8);
    }

    void ImageViewer::to32Bit()
    {
        toBitDepth(32);
    }

    void ImageViewer::toBitDepth(int d)
    {
        image = image.convertDepth(d);
        reconvertImage();
        repaint( image.hasAlphaBuffer() );
    }

Main:

    /****************************************************************************
    ** $Id: qt/main.cpp   3.3.5   edited Aug 31 12:13 $
    **
    ** 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 "showimg.h"
    #include "imagefip.h"
    #include <qapplication.h>
    #include <qimage.h>

    int main( int argc, char **argv )
    {
        if ( argc > 1 && QString(argv[1]) == "-m" ) {
            QApplication::setColorSpec( QApplication::ManyColor );
            argc--;
            argv++;
        }
        else if ( argc > 1 && QString(argv[1]) == "-n" ) {
            QApplication::setColorSpec( QApplication::NormalColor );
            argc--;
            argv++;
        }
        else {
            QApplication::setColorSpec( QApplication::CustomColor );
        }

        QApplication a( argc, argv );

        ImageIconProvider iip;
        QFileDialog::setIconProvider( &iip );

        if ( argc <= 1 ) {
            // Create a window which looks after its own existence.
            ImageViewer *w =
                new ImageViewer(0, "new window", Qt::WDestructiveClose | Qt::WResizeNoErase );
            w->setCaption("Qt Example - Image Viewer");
            w->show();
        } else {
            for ( int i=1; i<argc; i++ ) {
                // Create a window which looks after its own existence.
                ImageViewer *w =
                    new ImageViewer(0, argv[i], Qt::WDestructiveClose | Qt::WResizeNoErase );
                w->setCaption("Qt Example - Image Viewer");
                w->loadImage( argv[i] );
                w->show();
            }
        }

        QObject::connect(qApp, SIGNAL(lastWindowClosed()), qApp, SLOT(quit()));

        return a.exec();
    }

See also Examples.