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alphachannel.cpp

/****************************************************************************
**
** Copyright (C) 2006-2008 Trolltech ASA. All rights reserved.
**
** This file is part of the documentation of the Qt Toolkit.
**
** This file may be used under the terms of the GNU General Public
** License versions 2.0 or 3.0 as published by the Free Software
** Foundation and appearing in the files LICENSE.GPL2 and LICENSE.GPL3
** included in the packaging of this file.  Alternatively you may (at
** your option) use any later version of the GNU General Public
** License if such license has been publicly approved by Trolltech ASA
** (or its successors, if any) and the KDE Free Qt Foundation. In
** addition, as a special exception, Trolltech gives you certain
** additional rights. These rights are described in the Trolltech GPL
** Exception version 1.2, which can be found at
** http://www.trolltech.com/products/qt/gplexception/ and in the file
** GPL_EXCEPTION.txt in this package.
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#include <qapplication.h>
#include <qlabel.h>
#include <qpixmap.h>
#include <qprinter.h>
#include <qpainter.h>
#include <qfile.h>
#include <qdir.h>
#include <qfileinfo.h>

#if (QT_VERSION) >= 0x040000
#include <QtGui>
#include <QtCore>
#endif

00058 class MyClass : public QWidget
{
public:
     MyClass(QWidget *parent = 0) : QWidget(parent) { }

protected:
00064      void paintEvent(QPaintEvent *e)
     {
        /*QRadialGradient rg(50, 50, 50, 50, 50);
         rg.setColorAt(0, QColor::fromRgbF(1, 0, 0, 1));
         rg.setColorAt(1, QColor::fromRgbF(0, 0, 0, 0));
         QPainter pmp(&pm);
         pmp.fillRect(0, 0, 100, 100, rg);
         pmp.end();*/

      createImage();

      QPainter p(this);
      p.fillRect(rect(), Qt::white);

      p.drawPixmap(0, 0, pixmap);

      p.drawPixmap(100, 0, channelImage);
     }

00083     void createImage()
    {
//! [0]
      pixmap = QPixmap(100, 100);
      pixmap.fill(Qt::transparent);

      QRadialGradient gradient(50, 50, 50, 50, 50);
      gradient.setColorAt(0, QColor::fromRgbF(1, 0, 0, 1));
      gradient.setColorAt(1, QColor::fromRgbF(0, 0, 0, 0));
      QPainter painter(&pixmap);
      painter.fillRect(0, 0, 100, 100, gradient);

      channelImage = pixmap.alphaChannel();
      update();
//! [0]
    }

    QPixmap channelImage, pixmap; 
    QSize sizeHint() const { return QSize(500, 500); }
};

    

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

     MyClass cl;
     cl.show();
     QObject::connect(&app, SIGNAL(lastWindowClosed()), &app, SLOT(quit()));

     int ret = app.exec();
     return ret;
}

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