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imagescaling.cpp Example File
qtconcurrent/imagescaling/imagescaling.cpp

 /****************************************************************************
 **
 ** Copyright (C) 2007-2008 Nokia Corporation and/or its subsidiary(-ies). All rights reserved.
 **
 ** This file is part of the documentation of the Qt Toolkit.
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 ** Licensees holding a valid Qt License Agreement may use this file in
 ** accordance with the rights, responsibilities and obligations
 ** contained therein.  Please consult your licensing agreement or
 ** contact [email protected] if any conditions of this licensing
 ** agreement are not clear to you.
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 ** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
 ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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 ****************************************************************************/
 #include "imagescaling.h"
 #include "math.h"

 #ifndef QT_NO_CONCURRENT

 const int imageSize = 100;

 QImage scale(const QString &imageFileName)
 {
     QImage image(imageFileName);
     return image.scaled(QSize(imageSize, imageSize), Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
 }

 Images::Images(QWidget *parent)
 : QWidget(parent)
 {
     setWindowTitle(tr("Image loading and scaling example"));
     resize(800, 600);

     imageScaling = new QFutureWatcher<QImage>(this);
     connect(imageScaling, SIGNAL(resultReadyAt(int)), SLOT(showImage(int)));
     connect(imageScaling, SIGNAL(finished()), SLOT(finished()));

     openButton = new QPushButton(tr("Open Images"));
     connect(openButton, SIGNAL(clicked()), SLOT(open()));

     cancelButton = new QPushButton(tr("Cancel"));
     cancelButton->setEnabled(false);
     connect(cancelButton, SIGNAL(clicked()), imageScaling, SLOT(cancel()));

     QHBoxLayout *buttonLayout = new QHBoxLayout();
     buttonLayout->addWidget(openButton);
     buttonLayout->addWidget(cancelButton);
     buttonLayout->addStretch();

     imagesLayout = new QGridLayout();

     mainLayout = new QVBoxLayout();
     mainLayout->addLayout(buttonLayout);
     mainLayout->addLayout(imagesLayout);
     mainLayout->addStretch();
     setLayout(mainLayout);
 }

 Images::~Images()
 {
     imageScaling->cancel();
     imageScaling->waitForFinished();
 }

 void Images::open()
 {
     // Cancel and wait if we are already loading images.
     if (imageScaling->isRunning()) {
         imageScaling->cancel();
         imageScaling->waitForFinished();
     }

     // Show a file open dialog at QDesktopServices::PicturesLocation.
     QStringList files = QFileDialog::getOpenFileNames(this, tr("Select Images"),
                             QDesktopServices::storageLocation(QDesktopServices::PicturesLocation),
                             "*.jpg *.png");

     if (files.count() == 0)
         return;

     // Do a simple layout.
     qDeleteAll(labels);
     labels.clear();

     int dim = sqrt(qreal(files.count())) + 1;
     for (int i = 0; i < dim; ++i) {
         for (int j = 0; j < dim; ++j) {
             QLabel *imageLabel = new QLabel;
             imageLabel->setFixedSize(imageSize,imageSize);
             imagesLayout->addWidget(imageLabel,i,j);
             labels.append(imageLabel);
         }
     }

     // Use mapped to run the thread safe scale function on the files.
     imageScaling->setFuture(QtConcurrent::mapped(files, scale));

     openButton->setEnabled(false);
     cancelButton->setEnabled(true);
 }

 void Images::showImage(int num)
 {
     labels[num]->setPixmap(QPixmap::fromImage(imageScaling->resultAt(num)));
 }

 void Images::finished()
 {
     openButton->setEnabled(true);
     cancelButton->setEnabled(false);
 }

 #endif // QT_NO_CONCURRENT