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# imageviewer.cpp Example File
widgets/imageviewer/imageviewer.cpp

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        #include <QtGui>

        #include "imageviewer.h"

        ImageViewer::ImageViewer()
        {
            imageLabel = new QLabel;
            imageLabel->setBackgroundRole(QPalette::Base);
            imageLabel->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
            imageLabel->setScaledContents(true);

            scrollArea = new QScrollArea;
            scrollArea->setBackgroundRole(QPalette::Dark);
            scrollArea->setWidget(imageLabel);
            setCentralWidget(scrollArea);

            createActions();
            createMenus();

            setWindowTitle(tr("Image Viewer"));
            resize(500, 400);
        }

        void ImageViewer::open()
        {
            QString fileName = QFileDialog::getOpenFileName(this,
                                            tr("Open File"), QDir::currentPath());
            if (!fileName.isEmpty()) {
                QImage image(fileName);
                if (image.isNull()) {
                    QMessageBox::information(this, tr("Image Viewer"),
                                             tr("Cannot load %1.").arg(fileName));
                    return;
                }
                imageLabel->setPixmap(QPixmap::fromImage(image));
                scaleFactor = 1.0;

                printAct->setEnabled(true);
                fitToWindowAct->setEnabled(true);
                updateActions();

                if (!fitToWindowAct->isChecked())
                    imageLabel->adjustSize();
            }
        }

        void ImageViewer::print()
        {
            Q_ASSERT(imageLabel->pixmap());
            QPrintDialog dialog(&printer, this);
            if (dialog.exec()) {
                QPainter painter(&printer);
                QRect rect = painter.viewport();
                QSize size = imageLabel->pixmap()->size();
                size.scale(rect.size(), Qt::KeepAspectRatio);
                painter.setViewport(rect.x(), rect.y(), size.width(), size.height());
                painter.setWindow(imageLabel->pixmap()->rect());
                painter.drawPixmap(0, 0, *imageLabel->pixmap());
            }
        }

        void ImageViewer::zoomIn()
        {
            scaleImage(1.25);
        }

        void ImageViewer::zoomOut()
        {
            scaleImage(0.8);
        }

        void ImageViewer::normalSize()
        {
            imageLabel->adjustSize();
            scaleFactor = 1.0;
        }

        void ImageViewer::fitToWindow()
        {
            bool fitToWindow = fitToWindowAct->isChecked();
            scrollArea->setWidgetResizable(fitToWindow);
            if (!fitToWindow)
                imageLabel->adjustSize();

            updateActions();
        }

        void ImageViewer::about()
        {
            QMessageBox::about(this, tr("About Image Viewer"),
                    tr("<p>The <b>Image Viewer</b> example shows how to combine QLabel "
                       "and QScrollArea to display an image. QLabel is typically used "
                       "for displaying a text, but it can also display an image. "
                       "QScrollArea provides a scrolling view around another widget. "
                       "If the child widget exceeds the size of the frame, QScrollArea "
                       "automatically provides scroll bars. </p><p>The example "
                       "demonstrates how QLabel's ability to scale its contents "
                       "(QLabel::scaledContents), and QScrollArea's ability to "
                       "automatically resize its contents "
                       "(QScrollArea::widgetResizable), can be used to implement "
                       "zooming and scaling features. </p><p>In addition the example "
                       "shows how to use QPainter to print an image.</p>"));
        }

        void ImageViewer::createActions()
        {
            openAct = new QAction(tr("&Open..."), this);
            openAct->setShortcut(tr("Ctrl+O"));
            connect(openAct, SIGNAL(triggered()), this, SLOT(open()));

            printAct = new QAction(tr("&Print..."), this);
            printAct->setShortcut(tr("Ctrl+P"));
            printAct->setEnabled(false);
            connect(printAct, SIGNAL(triggered()), this, SLOT(print()));

            exitAct = new QAction(tr("E&xit"), this);
            exitAct->setShortcut(tr("Ctrl+Q"));
            connect(exitAct, SIGNAL(triggered()), this, SLOT(close()));

            zoomInAct = new QAction(tr("Zoom &In (25%)"), this);
            zoomInAct->setShortcut(tr("Ctrl++"));
            zoomInAct->setEnabled(false);
            connect(zoomInAct, SIGNAL(triggered()), this, SLOT(zoomIn()));

            zoomOutAct = new QAction(tr("Zoom &Out (25%)"), this);
            zoomOutAct->setShortcut(tr("Ctrl+-"));
            zoomOutAct->setEnabled(false);
            connect(zoomOutAct, SIGNAL(triggered()), this, SLOT(zoomOut()));

            normalSizeAct = new QAction(tr("&Normal Size"), this);
            normalSizeAct->setShortcut(tr("Ctrl+S"));
            normalSizeAct->setEnabled(false);
            connect(normalSizeAct, SIGNAL(triggered()), this, SLOT(normalSize()));

            fitToWindowAct = new QAction(tr("&Fit to Window"), this);
            fitToWindowAct->setEnabled(false);
            fitToWindowAct->setCheckable(true);
            fitToWindowAct->setShortcut(tr("Ctrl+F"));
            connect(fitToWindowAct, SIGNAL(triggered()), this, SLOT(fitToWindow()));

            aboutAct = new QAction(tr("&About"), this);
            connect(aboutAct, SIGNAL(triggered()), this, SLOT(about()));

            aboutQtAct = new QAction(tr("About &Qt"), this);
            connect(aboutQtAct, SIGNAL(triggered()), qApp, SLOT(aboutQt()));
        }

        void ImageViewer::createMenus()
        {
            fileMenu = new QMenu(tr("&File"), this);
            fileMenu->addAction(openAct);
            fileMenu->addAction(printAct);
            fileMenu->addSeparator();
            fileMenu->addAction(exitAct);

            viewMenu = new QMenu(tr("&View"), this);
            viewMenu->addAction(zoomInAct);
            viewMenu->addAction(zoomOutAct);
            viewMenu->addAction(normalSizeAct);
            viewMenu->addSeparator();
            viewMenu->addAction(fitToWindowAct);

            helpMenu = new QMenu(tr("&Help"), this);
            helpMenu->addAction(aboutAct);
            helpMenu->addAction(aboutQtAct);

            menuBar()->addMenu(fileMenu);
            menuBar()->addMenu(viewMenu);
            menuBar()->addMenu(helpMenu);
        }

        void ImageViewer::updateActions()
        {
            zoomInAct->setEnabled(!fitToWindowAct->isChecked());
            zoomOutAct->setEnabled(!fitToWindowAct->isChecked());
            normalSizeAct->setEnabled(!fitToWindowAct->isChecked());
        }

        void ImageViewer::scaleImage(double factor)
        {
            Q_ASSERT(imageLabel->pixmap());
            scaleFactor *= factor;
            imageLabel->resize(scaleFactor * imageLabel->pixmap()->size());

            adjustScrollBar(scrollArea->horizontalScrollBar(), factor);
            adjustScrollBar(scrollArea->verticalScrollBar(), factor);

            zoomInAct->setEnabled(scaleFactor < 3.0);
            zoomOutAct->setEnabled(scaleFactor > 0.333);
        }

        void ImageViewer::adjustScrollBar(QScrollBar *scrollBar, double factor)
        {
            scrollBar->setValue(int(factor * scrollBar->value()
                                    + ((factor - 1) * scrollBar->pageStep()/2)));
        }