Qt 5.9 | Qt Concurrent | Image Scaling Example | imagescaling.cpp Example File

Qt 5.9.9 Reference Documentation

# 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);
      }