imagescaling.cpp Example File

imagescaling/imagescaling.cpp
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 #include "imagescaling.h"

 #include <qmath.h>

 #include <functional>

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

     imageScaling = new QFutureWatcher<QImage>(this);
     connect(imageScaling, &QFutureWatcher<QImage>::resultReadyAt, this, &Images::showImage);
     connect(imageScaling, &QFutureWatcher<QImage>::finished, this, &Images::finished);

     openButton = new QPushButton(tr("Open Images"));
     connect(openButton, &QPushButton::clicked, this, &Images::open);

     cancelButton = new QPushButton(tr("Cancel"));
     cancelButton->setEnabled(false);
     connect(cancelButton, &QPushButton::clicked, imageScaling, &QFutureWatcher<QImage>::cancel);

     pauseButton = new QPushButton(tr("Pause/Resume"));
     pauseButton->setEnabled(false);
     connect(pauseButton, &QPushButton::clicked, imageScaling, &QFutureWatcher<QImage>::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 QStandardPaths::PicturesLocation.
     QStringList files = QFileDialog::getOpenFileNames(this, tr("Select Images"),
                             QStandardPaths::writableLocation(QStandardPaths::PicturesLocation),
                             "*.jpg *.png");

     if (files.isEmpty())
         return;

     const int imageSize = 100;

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

     int dim = qSqrt(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);
         }
     }

     std::function<QImage(const QString&)> scale = [imageSize](const QString &imageFileName) {
         QImage image(imageFileName);
         return image.scaled(QSize(imageSize, imageSize), Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
     };

     // 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);
 }