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# QMag

This is a simple magnifier-type program. It shows how one can do some quite low-level operations in a portable way using Qt.

Run it, click in the magnifier window, then click where you want to magnify or drag out a rectangle. Two combo boxes let you select amplification and refresh frequency, a text label tells you the color of the pixel the cursor is on, and a button lets you save the magnified area as a .bmp file.

Implementation:

    /****************************************************************************
    ** $Id: qt/qmag.cpp   3.3.8   edited Jan 11 14:37 $
    **
    ** Copyright (C) 1992-2007 Trolltech ASA.  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 <qcombobox.h>
    #include <qpushbutton.h>
    #include <qpixmap.h>
    #include <qimage.h>
    #include <qlabel.h>
    #include <qfiledialog.h>
    #include <qregexp.h>

    #include <qapplication.h>
    #include <qpainter.h>
    #include <qwmatrix.h>

    class MagWidget : public QWidget
    {
        Q_OBJECT
    public:
        MagWidget( QWidget *parent=0, const char *name=0 );

    public slots:
        void        setZoom( int );
        void        setRefresh( int );
        void        save();
        void        multiSave();

    protected:
        void        paintEvent( QPaintEvent * );
        void        mousePressEvent( QMouseEvent * );
        void        mouseReleaseEvent( QMouseEvent * );
        void        mouseMoveEvent( QMouseEvent * );
        void        focusOutEvent( QFocusEvent * );
        void        timerEvent( QTimerEvent * );
        void        resizeEvent( QResizeEvent * );

    private:
        void        grabAround(QPoint pos);
        void        grab();

        QComboBox   *zoom;
        QComboBox   *refresh;
        QPushButton *saveButton;
        QPushButton *multiSaveButton;
        QPushButton *quitButton;
        QPixmap     pm;             // pixmap, magnified
        QPixmap     p;              // pixmap
        QImage      image;          // image of pixmap (for RGB)
        QLabel      *rgb;
        int         yoffset;        // pixels in addition to the actual picture
        int         z;              // magnification factor
        int         r;              // autorefresh rate (index into refreshrates)
        bool        grabbing;       // TRUE if qmag is currently grabbing
        int         grabx, graby;
        QString     multifn;        // filename for multisave
    };

    #ifdef COMPLEX_GUI
    static const char *zoomfactors[] = {
        "100%", "200%", "300%", "400%", "500%",
        "600%", "700%", "800%", "1600%", 0 };

    static const char *refreshrates[] = {
        "No autorefresh", "50 per second", "4 per second", "3 per second", "2 per second",
        "Every second", "Every two seconds", "Every three seconds",
        "Every five seconds", "Every ten seconds", 0 };
    #endif

    static const int timer[] = {
        0, 20, 250, 333, 500, 1000, 2000, 3000, 5000, 10000 };

    MagWidget::MagWidget( QWidget *parent, const char *name )
        : QWidget( parent, name)
    {
        z = 1;                      // default zoom (100%)
        r = 0;                      // default refresh (none)

    #ifdef COMPLEX_GUI
        int w=0, x=0, n;

        zoom = new QComboBox( FALSE, this );
        Q_CHECK_PTR(zoom);
        zoom->insertStrList( zoomfactors, 9 );
        connect( zoom, SIGNAL(activated(int)), SLOT(setZoom(int)) );

        refresh = new QComboBox( FALSE, this );
        Q_CHECK_PTR(refresh);
        refresh->insertStrList( refreshrates, 9 );
        connect( refresh, SIGNAL(activated(int)), SLOT(setRefresh(int)) );

        for( n=0; n<9; n++) {
            int w2 = zoom->fontMetrics().width( zoomfactors[n] );
            w = QMAX(w2, w);
        }
        zoom->setGeometry( 2, 2, w+30, 20 );

        x = w+34;
        w = 0;
        for( n=0; n<9; n++) {
            int w2 = refresh->fontMetrics().width( refreshrates[n] );
            w = QMAX(w2, w);
        }
        refresh->setGeometry( x, 2, w+30, 20 );

        saveButton = new QPushButton( this );
        Q_CHECK_PTR(saveButton);
        connect( saveButton, SIGNAL(clicked()), this, SLOT(save()) );
        saveButton->setText( "Save" );
        saveButton->setGeometry( x+w+30+2, 2,
                                 10+saveButton->fontMetrics().width("Save"), 20 );

        multiSaveButton = new QPushButton( this );
        multiSaveButton->setToggleButton(TRUE);
        Q_CHECK_PTR(multiSaveButton);
        connect( multiSaveButton, SIGNAL(clicked()), this, SLOT(multiSave()) );
        multiSaveButton->setText( "MultiSave" );
        multiSaveButton->setGeometry( saveButton->geometry().right() + 2, 2,
                                 10+multiSaveButton->fontMetrics().width("MultiSave"), 20 );

        quitButton = new QPushButton( this );
        Q_CHECK_PTR(quitButton);
        connect( quitButton, SIGNAL(clicked()), qApp, SLOT(quit()) );
        quitButton->setText( "Quit" );
        quitButton->setGeometry( multiSaveButton->geometry().right() + 2, 2,
                                 10+quitButton->fontMetrics().width("Quit"), 20 );
    #else
        zoom = 0;
        multiSaveButton = 0;
    #endif

        setRefresh(1);
        setZoom(5);

        rgb = new QLabel( this );
        Q_CHECK_PTR( rgb );
        rgb->setText( "" );
        rgb->setAlignment( AlignVCenter );
        rgb->resize( width(), rgb->fontMetrics().height() + 4 );

    #ifdef COMPLEX_GUI
        yoffset = zoom->height()    // top buttons
            + 4                     // space around top buttons
            + rgb->height();        // color-value text height
        setMinimumSize( quitButton->pos().x(), yoffset+20 );
        resize( quitButton->geometry().topRight().x() + 2, yoffset+60 );
    #else
        yoffset = 0;
        resize(350,350);
    #endif

        grabx = graby = -1;
        grabbing = FALSE;

        setMouseTracking( TRUE );   // and do let me know what pixel I'm at, eh?

        grabAround( QPoint(grabx=qApp->desktop()->width()/2, graby=qApp->desktop()->height()/2) );
    }

    void MagWidget::setZoom( int index )
    {
        if (index == 8)
            z = 16;
        else
            z = index+1;
        grab();
    }

    void MagWidget::setRefresh( int index )
    {
        r = index;
        killTimers();
        if (index && !grabbing)
            startTimer( timer[r] );
    }

    void MagWidget::save()
    {
        if ( !p.isNull() ) {
            killTimers();
            QString fn = QFileDialog::getSaveFileName();
            if ( !fn.isEmpty() )
                p.save( fn, "BMP" );
            if ( r )
                startTimer( timer[r] );
        }
    }

    void MagWidget::multiSave()
    {
        if ( !p.isNull() ) {
            multifn = ""; // stops saving
            multifn = QFileDialog::getSaveFileName();
            if ( multifn.isEmpty() )
                multiSaveButton->setOn(FALSE);
            if ( !r )
                p.save( multifn, "BMP" );
        } else {
            multiSaveButton->setOn(FALSE);
        }
    }

    void MagWidget::grab()
    {
        if ( !isVisible() )
            return;                 // don't eat resources when iconified

        if ( grabx < 0 || graby < 0 )
            return;                 // don't grab until the user has said to

        int x,y, w,h;

        w = (width()+z-1)/z;
        h = (height()+z-1-yoffset)/z;
        if ( w<1 || h<1 )
            return;                 // don't ask too much from the window system :)

        x = grabx-w/2;              // find a suitable position to grab from
        y = graby-h/2;
        if ( x + w > QApplication::desktop()->width() )
            x = QApplication::desktop()->width()-w;
        else if ( x < 0 )
            x = 0;
        if ( y + h > QApplication::desktop()->height() )
            y = QApplication::desktop()->height()-h;
        else if ( y < 0 )
            y = 0;

        p = QPixmap::grabWindow( QApplication::desktop()->winId(),  x, y, w, h );
        image = p.convertToImage();
        QWMatrix m;                 // after getting it, scale it
        m.scale( (double)z, (double)z );
        pm = p.xForm( m );

        if ( !multiSaveButton || !multiSaveButton->isOn() )
            repaint( FALSE );               // and finally repaint, flicker-free
    }

    void MagWidget::paintEvent( QPaintEvent * )
    {
        if ( !pm.isNull() ) {
            QPainter paint( this );
            paint.drawPixmap( 0, zoom ? zoom->height()+4 : 0, pm,
                                  0,0, width(), height()-yoffset );
        }
    }

    void MagWidget::mousePressEvent( QMouseEvent *e )
    {
        if ( !grabbing ) {          // prepare to grab...
            grabbing = TRUE;
            killTimers();
            grabMouse( crossCursor );
            grabx = -1;
            graby = -1;
        } else {                    // REALLY prepare to grab
            grabx = mapToGlobal(e->pos()).x();
            graby = mapToGlobal(e->pos()).y();
        }
    }

    void MagWidget::mouseReleaseEvent( QMouseEvent * e )
    {
        if ( grabbing && grabx >= 0 && graby >= 0 ) {
            grabbing = FALSE;
            grabAround(e->pos());
            releaseMouse();
        }
    }

    void MagWidget::grabAround(QPoint pos)
    {
        int rx, ry;
        rx = mapToGlobal(pos).x();
        ry = mapToGlobal(pos).y();
        int w = QABS(rx-grabx);
        int h = QABS(ry-graby);
        if ( w > 10 && h > 10 ) {
            int pz;
            pz = 1;
            while ( w*pz*h*pz < width()*(height()-yoffset) &&
                    w*pz < QApplication::desktop()->width() &&
                    h*pz < QApplication::desktop()->height() )
                pz++;
            if ( (w*pz*h*pz - width()*(height()-yoffset)) >
                 (width()*(height()-yoffset) - w*(pz-1)*h*(pz-1)) )
                pz--;
            if ( pz < 1 )
                pz = 1;
            if ( pz > 8 )
                pz = 8;
            if ( zoom )
                zoom->setCurrentItem( pz-1 );

            z = pz;
            grabx = QMIN(rx, grabx) + w/2;
            graby = QMIN(ry, graby) + h/2;
            resize( w*z, h*z+yoffset );
        }
        grab();
        if ( r )
            startTimer( timer[r] );
    }

    void MagWidget::mouseMoveEvent( QMouseEvent *e )
    {
        if ( grabbing || pm.isNull() ||
             e->pos().y() > height() - (zoom ? zoom->fontMetrics().height() - 4 : 0) ||
             e->pos().y() < (zoom ? zoom->height()+4 : 4) ) {
            rgb->setText( "" );
        } else {
            int x,y;
            x = e->pos().x() / z;
            y = (e->pos().y() - ( zoom ? zoom->height() : 0 ) - 4) / z;
            QString pixelinfo;
            if ( image.valid(x,y) )
            {
                QRgb px = image.pixel(x,y);
                pixelinfo.sprintf(" %3d,%3d,%3d  #%02x%02x%02x",
                    qRed(px), qGreen(px), qBlue(px),
                    qRed(px), qGreen(px), qBlue(px));
            }
            QString label;
            label.sprintf( "x=%d, y=%d %s",
                x+grabx, y+graby, (const char*)pixelinfo );
            rgb->setText( label );
        }
    }

    void MagWidget::focusOutEvent( QFocusEvent * )
    {
        rgb->setText( "" );
    }

    void MagWidget::timerEvent( QTimerEvent * )
    {
        grab();
    /*
        if ( multiSaveButton->isOn() && !multifn.isEmpty() ) {
            QRegExp num("[0-9][0-9]*");
            int start;
            int len;
            if ((start=num.match(multifn,0,&len))>=0)
                multifn.replace(num,
                    QString().setNum(multifn.mid(start,len).toInt()+1)
                );
            p.save( multifn, "BMP" );
        }
    */
    }

    void MagWidget::resizeEvent( QResizeEvent * )
    {
        rgb->setGeometry( 0, height() - rgb->height(), width(), rgb->height() );
        grab();
    }

    #include "qmag.moc"

    int main( int argc, char **argv )
    {
        QApplication a( argc, argv );
        MagWidget m;
        a.setMainWidget( &m );
        m.show();
        return a.exec();
    }

See also Examples.