- Qt 5.5
- Qt Concurrent
- Image Scaling Example
- imagescaling.cpp Example File
- Qt 5.5.1 Reference Documentation

# imagescaling.cpp Example File

imagescaling/imagescaling.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2015 The Qt Company Ltd.
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
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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);
    }