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# Scrollview

This example shows how to use Qt's scrollview. This is a widget optimized for very large contents.

Implementation:

    /****************************************************************************
    ** $Id: qt/scrollview.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 <qscrollview.h>
    #include <qapplication.h>
    #include <qmenubar.h>
    #include <qpopupmenu.h>
    #include <qpushbutton.h>
    #include <qpainter.h>
    #include <qpixmap.h>
    #include <qmessagebox.h>
    #include <qlayout.h>
    #include <qlabel.h>
    #include <qmultilineedit.h>
    #include <qsizegrip.h>
    #include <stdlib.h>

    static const int style_id       = 0x1000;
    static const int lw_id          = 0x2000;
    static const int mlw_id         = 0x4000;
    static const int mw_id          = 0x8000;
    static const int max_lw         = 16;
    static const int max_mlw        = 5;
    static const int max_mw         = 10;

    class BigShrinker : public QFrame {
        Q_OBJECT
    public:
        BigShrinker(QWidget* parent) :
            QFrame(parent)
        {
            setFrameStyle(QFrame::Box|QFrame::Sunken);
            int h=35;
            int b=0;
            for (int y=0; y<2000-h; y+=h+10) {
                if (y == 0) {
                    QButton* q=new QPushButton("Quit", this);
                    connect(q, SIGNAL(clicked()), qApp, SLOT(quit()));
                } else {
                    QString str;
                    if ( b > 0 ) {
                        str.sprintf("Button %d", b++);
                    } else {
                        str = "I'm shrinking!";
                        ++b;
                    }
                    (new QPushButton(str, this))->move(y/2,y);
                }
            }
            resize(1000,2000);

            startTimer(250);
        }

        void timerEvent(QTimerEvent*)
        {
            int w=width();
            int h=height();
            if ( w > 50 ) w -= 1;
            if ( h > 50 ) h -= 2;
            resize(w,h);
        }

        void mouseReleaseEvent(QMouseEvent* e)
        {
            emit clicked(e->x(), e->y());
        }

    signals:
        void clicked(int,int);
    };

    class BigMatrix : public QScrollView {
        QMultiLineEdit *dragging;
    public:
        BigMatrix(QWidget* parent) :
            QScrollView(parent,"matrix", WStaticContents),
            bg("bg.ppm")
        {
            bg.load("bg.ppm");
            resizeContents(400000,300000);

            dragging = 0;
        }

        void viewportMousePressEvent(QMouseEvent* e)
        {
            int x, y;
            viewportToContents( e->x(),  e->y(), x, y );
            dragging = new QMultiLineEdit(viewport(),"Another");
            dragging->setText("Thanks!");
            dragging->resize(100,100);
            addChild(dragging, x, y);
            showChild(dragging);
        }

        void viewportMouseReleaseEvent(QMouseEvent*)
        {
            dragging = 0;
        }

        void viewportMouseMoveEvent(QMouseEvent* e)
        {
            if ( dragging ) {
                int mx, my;
                viewportToContents( e->x(),  e->y(), mx, my );
                int cx = childX(dragging);
                int cy = childY(dragging);
                int w = mx - cx + 1;
                int h = my - cy + 1;
                QString msg;
                msg.sprintf("at (%d,%d) %d by %d",cx,cy,w,h);
                dragging->setText(msg);
                dragging->resize(w,h);
            }
        }

    protected:
        void drawContents(QPainter* p, int cx, int cy, int cw, int ch)
        {
            // The Background
            if ( !bg.isNull() ) {
                int rowheight=bg.height();
                int toprow=cy/rowheight;
                int bottomrow=(cy+ch+rowheight-1)/rowheight;
                int colwidth=bg.width();
                int leftcol=cx/colwidth;
                int rightcol=(cx+cw+colwidth-1)/colwidth;
                for (int r=toprow; r<=bottomrow; r++) {
                    int py=r*rowheight;
                    for (int c=leftcol; c<=rightcol; c++) {
                        int px=c*colwidth;
                        p->drawPixmap(px, py, bg);
                    }
                }
            } else {
                p->fillRect(cx, cy, cw, ch, QColor(240,222,208));
            }

            // The Numbers
            {
                QFontMetrics fm=p->fontMetrics();
                int rowheight=fm.lineSpacing();
                int toprow=cy/rowheight;
                int bottomrow=(cy+ch+rowheight-1)/rowheight;
                int colwidth=fm.width("00000,000000 ")+3;
                int leftcol=cx/colwidth;
                int rightcol=(cx+cw+colwidth-1)/colwidth;
                QString str;
                for (int r=toprow; r<=bottomrow; r++) {
                    int py=r*rowheight;
                    for (int c=leftcol; c<=rightcol; c++) {
                        int px=c*colwidth;
                        str.sprintf("%d,%d",c,r);
                        p->drawText(px+3, py+fm.ascent(), str);
                    }
                }

                // The Big Hint
                if (leftcol<10 && toprow<5) {
                    p->setFont(QFont("Charter",30));
                    p->setPen(red);
                    QString text;
                    text.sprintf("HINT:  Look at %d,%d",215000/colwidth,115000/rowheight);
                    p->drawText(100,50,text);
                }
            }

            // The Big X
            {
                if (cx+cw>200000 && cy+ch>100000 && cx<230000 && cy<130000) {
                    // Note that some X server cannot even handle co-ordinates
                    // beyond about 4000, so you might not see this.
                    p->drawLine(200000,100000,229999,129999);
                    p->drawLine(229999,100000,200000,129999);

                    // X marks the spot!
                    p->setFont(QFont("Charter",100));
                    p->setPen(blue);
                    p->drawText(215000-500,115000-100,1000,200,AlignCenter,"YOU WIN!!!!!");
                }
            }
        }

    private:
        QPixmap bg;
    };

    class ScrollViewExample : public QWidget {
        Q_OBJECT

    public:
        ScrollViewExample(int technique, QWidget* parent=0, const char* name=0) :
            QWidget(parent,name)
        {
            QMenuBar* menubar = new QMenuBar(this);
            Q_CHECK_PTR( menubar );

            QPopupMenu* file = new QPopupMenu( menubar );
            Q_CHECK_PTR( file );
            menubar->insertItem( "&File", file );
            file->insertItem( "Quit", qApp,  SLOT(quit()) );

            vp_options = new QPopupMenu( menubar );
            Q_CHECK_PTR( vp_options );
            vp_options->setCheckable( TRUE );
            menubar->insertItem( "&ScrollView", vp_options );
            connect( vp_options, SIGNAL(activated(int)),
                this, SLOT(doVPMenuItem(int)) );

            vauto_id = vp_options->insertItem( "Vertical Auto" );
            vaoff_id = vp_options->insertItem( "Vertical AlwaysOff" );
            vaon_id = vp_options->insertItem( "Vertical AlwaysOn" );
            vp_options->insertSeparator();
            hauto_id = vp_options->insertItem( "Horizontal Auto" );
            haoff_id = vp_options->insertItem( "Horizontal AlwaysOff" );
            haon_id = vp_options->insertItem( "Horizontal AlwaysOn" );
            vp_options->insertSeparator();
            corn_id = vp_options->insertItem( "cornerWidget" );

            if (technique == 1) {
                vp = new QScrollView(this);
                BigShrinker *bs = new BigShrinker(0);//(vp->viewport());
                vp->addChild(bs);
                bs->setAcceptDrops(TRUE);
                QObject::connect(bs, SIGNAL(clicked(int,int)),
                                vp, SLOT(center(int,int)));
            } else {
                vp = new BigMatrix(this);
                if ( technique == 3 )
                    vp->enableClipper(TRUE);
                srand(1);
                for (int i=0; i<30; i++) {
                    QMultiLineEdit *l = new QMultiLineEdit(vp->viewport(),"First");
                    l->setText("Drag out more of these.");
                    l->resize(100,100);
                    vp->addChild(l, rand()%800, rand()%10000);
                }
                vp->viewport()->setBackgroundMode(NoBackground);
            }

            f_options = new QPopupMenu( menubar );
            Q_CHECK_PTR( f_options );
            f_options->setCheckable( TRUE );
            menubar->insertItem( "F&rame", f_options );
            connect( f_options, SIGNAL(activated(int)),
                this, SLOT(doFMenuItem(int)) );

            f_options->insertItem( "No Frame", style_id );
            f_options->insertItem( "Box", style_id|QFrame::Box );
            f_options->insertItem( "Panel", style_id|QFrame::Panel );
            f_options->insertItem( "WinPanel", style_id|QFrame::WinPanel );
            f_options->insertSeparator();
            f_options->insertItem( "Plain", style_id|QFrame::Plain );
            f_options->insertItem( "Raised", style_id|QFrame::Raised );
            f_laststyle = f_options->indexOf(
                f_options->insertItem( "Sunken", style_id|QFrame::Sunken ));
            f_options->insertSeparator();
            lw_options = new QPopupMenu( menubar );
            Q_CHECK_PTR( lw_options );
            lw_options->setCheckable( TRUE );
            for (int lw = 1; lw <= max_lw; lw++) {
                QString str;
                str.sprintf("%d Pixels", lw);
                lw_options->insertItem( str, lw_id | lw );
            }
            f_options->insertItem( "Line Width", lw_options );
            connect( lw_options, SIGNAL(activated(int)),
                this, SLOT(doFMenuItem(int)) );
            mlw_options = new QPopupMenu( menubar );
            Q_CHECK_PTR( mlw_options );
            mlw_options->setCheckable( TRUE );
            for (int mlw = 0; mlw <= max_mlw; mlw++) {
                QString str;
                str.sprintf("%d Pixels", mlw);
                mlw_options->insertItem( str, mlw_id | mlw );
            }
            f_options->insertItem( "Midline Width", mlw_options );
            connect( mlw_options, SIGNAL(activated(int)),
                this, SLOT(doFMenuItem(int)) );
            mw_options = new QPopupMenu( menubar );
            Q_CHECK_PTR( mw_options );
            mw_options->setCheckable( TRUE );
            for (int mw = 0; mw <= max_mw; mw++) {
                QString str;
                str.sprintf("%d Pixels", mw);
                mw_options->insertItem( str, mw_id | mw );
            }
            f_options->insertItem( "Margin Width", mw_options );
            connect( mw_options, SIGNAL(activated(int)),
                this, SLOT(doFMenuItem(int)) );

            setVPMenuItems();
            setFMenuItems();

            QVBoxLayout* vbox = new QVBoxLayout(this);
            vbox->setMenuBar(menubar);
            menubar->setSeparator(QMenuBar::InWindowsStyle);
            vbox->addWidget(vp);
            vbox->activate();

            corner = new QSizeGrip(this);
            corner->hide();
        }

    private slots:
        void doVPMenuItem(int id)
        {
            if (id == vauto_id ) {
                vp->setVScrollBarMode(QScrollView::Auto);
            } else if (id == vaoff_id) {
                vp->setVScrollBarMode(QScrollView::AlwaysOff);
            } else if (id == vaon_id) {
                vp->setVScrollBarMode(QScrollView::AlwaysOn);
            } else if (id == hauto_id) {
                vp->setHScrollBarMode(QScrollView::Auto);
            } else if (id == haoff_id) {
                vp->setHScrollBarMode(QScrollView::AlwaysOff);
            } else if (id == haon_id) {
                vp->setHScrollBarMode(QScrollView::AlwaysOn);
            } else if (id == corn_id) {
                bool corn = !vp->cornerWidget();
                vp->setCornerWidget(corn ? corner : 0);
            } else {
                return; // Not for us to process.
            }
            setVPMenuItems();
        }

        void setVPMenuItems()
        {
            QScrollView::ScrollBarMode vm = vp->vScrollBarMode();
            vp_options->setItemChecked( vauto_id, vm == QScrollView::Auto );
            vp_options->setItemChecked( vaoff_id, vm == QScrollView::AlwaysOff );
            vp_options->setItemChecked( vaon_id, vm == QScrollView::AlwaysOn );

            QScrollView::ScrollBarMode hm = vp->hScrollBarMode();
            vp_options->setItemChecked( hauto_id, hm == QScrollView::Auto );
            vp_options->setItemChecked( haoff_id, hm == QScrollView::AlwaysOff );
            vp_options->setItemChecked( haon_id, hm == QScrollView::AlwaysOn );

            vp_options->setItemChecked( corn_id, !!vp->cornerWidget() );
        }

        void doFMenuItem(int id)
        {
            if (id & style_id) {
                int sty;

                if (id == style_id) {
                    sty = 0;
                } else if (id & QFrame::MShape) {
                    sty = vp->frameStyle()&QFrame::MShadow;
                    sty = (sty ? sty : QFrame::Plain) | (id&QFrame::MShape);
                } else {
                    sty = vp->frameStyle()&QFrame::MShape;
                    sty = (sty ? sty : QFrame::Box) | (id&QFrame::MShadow);
                }
                vp->setFrameStyle(sty);
            } else if (id & lw_id) {
                vp->setLineWidth(id&~lw_id);
            } else if (id & mlw_id) {
                vp->setMidLineWidth(id&~mlw_id);
            } else {
                vp->setMargin(id&~mw_id);
            }

            vp->update();
            setFMenuItems();
        }

        void setFMenuItems()
        {
            int sty = vp->frameStyle();

            f_options->setItemChecked( style_id, !sty );

            for (int i=1; i <= f_laststyle; i++) {
                int id = f_options->idAt(i);
                if (id & QFrame::MShape)
                    f_options->setItemChecked( id,
                        ((id&QFrame::MShape) == (sty&QFrame::MShape)) );
                else
                    f_options->setItemChecked( id,
                        ((id&QFrame::MShadow) == (sty&QFrame::MShadow)) );
            }

            for (int lw=1; lw<=max_lw; lw++)
                lw_options->setItemChecked( lw_id|lw, vp->lineWidth() == lw );

            for (int mlw=0; mlw<=max_mlw; mlw++)
                mlw_options->setItemChecked( mlw_id|mlw, vp->midLineWidth() == mlw );

            for (int mw=0; mw<=max_mw; mw++)
                mw_options->setItemChecked( mw_id|mw, vp->margin() == mw );
        }

    private:
        QScrollView* vp;
        QPopupMenu* vp_options;
        QPopupMenu* f_options;
        QPopupMenu* lw_options;
        QPopupMenu* mlw_options;
        QPopupMenu* mw_options;
        QSizeGrip* corner;

        int vauto_id, vaoff_id, vaon_id,
            hauto_id, haoff_id, haon_id,
            corn_id;

        int f_laststyle;
    };

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

        ScrollViewExample ve1(1,0,"ve1");
        ScrollViewExample ve2(2,0,"ve2");
        ScrollViewExample ve3(3,0,"ve3");
        ve1.setCaption("Qt Example - Scrollviews");
        ve1.show();
        ve2.setCaption("Qt Example - Scrollviews");
        ve2.show();
        ve3.setCaption("Qt Example - Scrollviews");
        ve3.show();

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

        return a.exec();
    }

    #include "scrollview.moc"

See also Examples.