imagescaling.cpp Example File

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  #include "imagescaling.h"
  #include <qmath.h>

  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 QStandardPaths::PicturesLocation.
      QStringList files = QFileDialog::getOpenFileNames(this, tr("Select Images"),
                              QStandardPaths::writableLocation(QStandardPaths::PicturesLocation),
                              "*.jpg *.png");

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

      // 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);
          }
      }

      // 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);
  }