Question

This example implements the famous scribble example. You can draw around in the canvas with different pens and save the result as picture.

---

Header file:

/****************************************************************************
** $Id:  qt/scribble.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 SCRIBBLE_H
#define SCRIBBLE_H

#include <qmainwindow.h>
#include <qpen.h>
#include <qpoint.h>
#include <qpixmap.h>
#include <qwidget.h>
#include <qstring.h>
#include <qpointarray.h>

class QMouseEvent;
class QResizeEvent;
class QPaintEvent;
class QToolButton;
class QSpinBox;

class Canvas : public QWidget
{
    Q_OBJECT

public:
    Canvas( QWidget *parent = 0, const char *name = 0 );

    void setPenColor( const QColor &c )
    { pen.setColor( c ); }

    void setPenWidth( int w )
    { pen.setWidth( w ); }

    QColor penColor()
    { return pen.color(); }

    int penWidth()
    { return pen.width(); }

    void save( const QString &filename, const QString &format );

    void clearScreen();

protected:
    void mousePressEvent( QMouseEvent *e );
    void mouseReleaseEvent( QMouseEvent *e );
    void mouseMoveEvent( QMouseEvent *e );
    void resizeEvent( QResizeEvent *e );
    void paintEvent( QPaintEvent *e );

    QPen pen;
    QPointArray polyline;

    bool mousePressed;

    QPixmap buffer;

};

class Scribble : public QMainWindow
{
    Q_OBJECT

public:
    Scribble( QWidget *parent = 0, const char *name = 0 );

protected:
    Canvas* canvas;

    QSpinBox *bPWidth;
    QToolButton *bPColor, *bSave, *bClear;

protected slots:
    void slotSave();
    void slotColor();
    void slotWidth( int );
    void slotClear();

};

#endif

---

Implementation:

/****************************************************************************
** $Id:  qt/scribble.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 "scribble.h"

#include <qapplication.h>
#include <qevent.h>
#include <qpainter.h>
#include <qtoolbar.h>
#include <qtoolbutton.h>
#include <qspinbox.h>
#include <qtooltip.h>
#include <qrect.h>
#include <qpoint.h>
#include <qcolordialog.h>
#include <qfiledialog.h>
#include <qcursor.h>
#include <qimage.h>
#include <qstrlist.h>
#include <qpopupmenu.h>
#include <qintdict.h>

const bool no_writing = FALSE;

Canvas::Canvas( QWidget *parent, const char *name )
    : QWidget( parent, name, WStaticContents ), pen( Qt::red, 3 ), polyline(3),
      mousePressed( FALSE ), buffer( width(), height() )
{

    if ((qApp->argc() > 0) && !buffer.load(qApp->argv()[1]))
        buffer.fill( colorGroup().base() );
    setBackgroundMode( QWidget::PaletteBase );
#ifndef QT_NO_CURSOR
    setCursor( Qt::crossCursor );
#endif
}

void Canvas::save( const QString &filename, const QString &format )
{
    if ( !no_writing )
        buffer.save( filename, format.upper() );
}

void Canvas::clearScreen()
{
    buffer.fill( colorGroup().base() );
    repaint( FALSE );
}

void Canvas::mousePressEvent( QMouseEvent *e )
{
    mousePressed = TRUE;
    polyline[2] = polyline[1] = polyline[0] = e->pos();
}

void Canvas::mouseReleaseEvent( QMouseEvent * )
{
    mousePressed = FALSE;
}

void Canvas::mouseMoveEvent( QMouseEvent *e )
{
    if ( mousePressed ) {
        QPainter painter;
        painter.begin( &buffer );
        painter.setPen( pen );
        polyline[2] = polyline[1];
        polyline[1] = polyline[0];
        polyline[0] = e->pos();
        painter.drawPolyline( polyline );
        painter.end();

        QRect r = polyline.boundingRect();
        r = r.normalize();
        r.setLeft( r.left() - penWidth() );
        r.setTop( r.top() - penWidth() );
        r.setRight( r.right() + penWidth() );
        r.setBottom( r.bottom() + penWidth() );

        bitBlt( this, r.x(), r.y(), &buffer, r.x(), r.y(), r.width(), r.height() );
    }
}

void Canvas::resizeEvent( QResizeEvent *e )
{
    QWidget::resizeEvent( e );

    int w = width() > buffer.width() ?
            width() : buffer.width();
    int h = height() > buffer.height() ?
            height() : buffer.height();

    QPixmap tmp( buffer );
    buffer.resize( w, h );
    buffer.fill( colorGroup().base() );
    bitBlt( &buffer, 0, 0, &tmp, 0, 0, tmp.width(), tmp.height() );
}

void Canvas::paintEvent( QPaintEvent *e )
{
    QWidget::paintEvent( e );

    QMemArray<QRect> rects = e->region().rects();
    for ( uint i = 0; i < rects.count(); i++ ) {
        QRect r = rects[(int)i];
        bitBlt( this, r.x(), r.y(), &buffer, r.x(), r.y(), r.width(), r.height() );
    }
}

//------------------------------------------------------

Scribble::Scribble( QWidget *parent, const char *name )
    : QMainWindow( parent, name )
{
    canvas = new Canvas( this );
    setCentralWidget( canvas );

    QToolBar *tools = new QToolBar( this );

    bSave = new QToolButton( QPixmap(), "Save", "Save as PNG image", this, SLOT( slotSave() ), tools );
    bSave->setText( "Save as..." );

    tools->addSeparator();

    bPColor = new QToolButton( QPixmap(), "Choose Pen Color", "Choose Pen Color", this, SLOT( slotColor() ), tools );
    bPColor->setText( "Choose Pen Color..." );

    tools->addSeparator();

    bPWidth = new QSpinBox( 1, 20, 1, tools );
    QToolTip::add( bPWidth, "Choose Pen Width" );
    connect( bPWidth, SIGNAL( valueChanged( int ) ), this, SLOT( slotWidth( int ) ) );
    bPWidth->setValue( 3 );

    tools->addSeparator();

    bClear = new QToolButton( QPixmap(), "Clear Screen", "Clear Screen", this, SLOT( slotClear() ), tools );
    bClear->setText( "Clear Screen" );
}

void Scribble::slotSave()
{
    QPopupMenu *menu = new QPopupMenu( 0 );
    QIntDict<QString> formats;
    formats.setAutoDelete( TRUE );

    for ( unsigned int i = 0; i < QImageIO::outputFormats().count(); i++ ) {
        QString str = QString( QImageIO::outputFormats().at( i ) );
        formats.insert( menu->insertItem( QString( "%1..." ).arg( str ) ), new QString( str ) );
    }

    menu->setMouseTracking( TRUE );
    int id = menu->exec( bSave->mapToGlobal( QPoint( 0, bSave->height() + 1 ) ) );

    if ( id != -1 ) {
        QString format = *formats[ id ];

        QString filename = QFileDialog::getSaveFileName( QString::null, QString( "*.%1" ).arg( format.lower() ), this );
        if ( !filename.isEmpty() )
            canvas->save( filename, format );
    }

    delete menu;
}

void Scribble::slotColor()
{
    QColor c = QColorDialog::getColor( canvas->penColor(), this );
    if ( c.isValid() )
        canvas->setPenColor( c );
}

void Scribble::slotWidth( int w )
{
    canvas->setPenWidth( w );
}

void Scribble::slotClear()
{
    canvas->clearScreen();
}

---

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


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

    Scribble scribble;

    scribble.resize( 500, 350 );
    scribble.setCaption("Qt Example - Scribble");
    a.setMainWidget( &scribble );
    if ( QApplication::desktop()->width() > 550
         && QApplication::desktop()->height() > 366 )
        scribble.show();
    else
        scribble.showMaximized();
    return a.exec();
}

See also Examples.