Qt Reference Documentation

# imagescaling.cpp Example File

qtconcurrent/imagescaling/imagescaling.cpp

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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()));

         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