imagescaling.cpp Example File

qtconcurrent/imagescaling/imagescaling.cpp
 /****************************************************************************
 **
 ** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
 ** All rights reserved.
 ** Contact: Nokia Corporation (qt-info@nokia.com)
 **
 ** This file is part of the examples of the Qt Toolkit.
 **
 ** $QT_BEGIN_LICENSE:BSD$
 ** You may use this file under the terms of the BSD license as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
 **     the names of its contributors may be used to endorse or promote
 **     products derived from this software without specific prior written
 **     permission.
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 ** $QT_END_LICENSE$
 **
 ****************************************************************************/
 #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()));

     pauseButton = new QPushButton(tr("Pause/Resume"));
     pauseButton->setEnabled(false);
     connect(pauseButton, SIGNAL(clicked()), imageScaling, SLOT(togglePaused()));

     QHBoxLayout *buttonLayout = new QHBoxLayout();
     buttonLayout->addWidget(openButton);
     buttonLayout->addWidget(cancelButton);
     buttonLayout->addWidget(pauseButton);
     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);
     pauseButton->setEnabled(true);
 }

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

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

 #endif // QT_NO_CONCURRENT