imageviewer.cpp Example File | Qt Widgets 5.12.12

- Qt 5.12
- Qt Widgets
- Image Viewer Example
- imageviewer.cpp Example File
- Qt 5.12.12 Reference Documentation

# imageviewer.cpp Example File

widgets/imageviewer/imageviewer.cpp

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     #include <QtWidgets>
     #if defined(QT_PRINTSUPPORT_LIB)
     #include <QtPrintSupport/qtprintsupportglobal.h>
     #if QT_CONFIG(printdialog)
     #include <QPrintDialog>
     #endif
     #endif

     #include "imageviewer.h"

     ImageViewer::ImageViewer()
        : imageLabel(new QLabel)
        , scrollArea(new QScrollArea)
        , scaleFactor(1)
     {
         imageLabel->setBackgroundRole(QPalette::Base);
         imageLabel->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
         imageLabel->setScaledContents(true);

         scrollArea->setBackgroundRole(QPalette::Dark);
         scrollArea->setWidget(imageLabel);
         scrollArea->setVisible(false);
         setCentralWidget(scrollArea);

         createActions();

         resize(QGuiApplication::primaryScreen()->availableSize() * 3 / 5);
     }

     bool ImageViewer::loadFile(const QString &fileName)
     {
         QImageReader reader(fileName);
         reader.setAutoTransform(true);
         const QImage newImage = reader.read();
         if (newImage.isNull()) {
             QMessageBox::information(this, QGuiApplication::applicationDisplayName(),
                                      tr("Cannot load %1: %2")
                                      .arg(QDir::toNativeSeparators(fileName), reader.errorString()));
             return false;
         }

         setImage(newImage);

         setWindowFilePath(fileName);

         const QString message = tr("Opened \"%1\", %2x%3, Depth: %4")
             .arg(QDir::toNativeSeparators(fileName)).arg(image.width()).arg(image.height()).arg(image.depth());
         statusBar()->showMessage(message);
         return true;
     }

     void ImageViewer::setImage(const QImage &newImage)
     {
         image = newImage;
         imageLabel->setPixmap(QPixmap::fromImage(image));
         scaleFactor = 1.0;

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

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

     bool ImageViewer::saveFile(const QString &fileName)
     {
         QImageWriter writer(fileName);

         if (!writer.write(image)) {
             QMessageBox::information(this, QGuiApplication::applicationDisplayName(),
                                      tr("Cannot write %1: %2")
                                      .arg(QDir::toNativeSeparators(fileName)), writer.errorString());
             return false;
         }
         const QString message = tr("Wrote \"%1\"").arg(QDir::toNativeSeparators(fileName));
         statusBar()->showMessage(message);
         return true;
     }

     static void initializeImageFileDialog(QFileDialog &dialog, QFileDialog::AcceptMode acceptMode)
     {
         static bool firstDialog = true;

         if (firstDialog) {
             firstDialog = false;
             const QStringList picturesLocations = QStandardPaths::standardLocations(QStandardPaths::PicturesLocation);
             dialog.setDirectory(picturesLocations.isEmpty() ? QDir::currentPath() : picturesLocations.last());
         }

         QStringList mimeTypeFilters;
         const QByteArrayList supportedMimeTypes = acceptMode == QFileDialog::AcceptOpen
             ? QImageReader::supportedMimeTypes() : QImageWriter::supportedMimeTypes();
         foreach (const QByteArray &mimeTypeName, supportedMimeTypes)
             mimeTypeFilters.append(mimeTypeName);
         mimeTypeFilters.sort();
         dialog.setMimeTypeFilters(mimeTypeFilters);
         dialog.selectMimeTypeFilter("image/jpeg");
         if (acceptMode == QFileDialog::AcceptSave)
             dialog.setDefaultSuffix("jpg");
     }

     void ImageViewer::open()
     {
         QFileDialog dialog(this, tr("Open File"));
         initializeImageFileDialog(dialog, QFileDialog::AcceptOpen);

         while (dialog.exec() == QDialog::Accepted && !loadFile(dialog.selectedFiles().first())) {}
     }

     void ImageViewer::saveAs()
     {
         QFileDialog dialog(this, tr("Save File As"));
         initializeImageFileDialog(dialog, QFileDialog::AcceptSave);

         while (dialog.exec() == QDialog::Accepted && !saveFile(dialog.selectedFiles().first())) {}
     }

     void ImageViewer::print()
     {
         Q_ASSERT(imageLabel->pixmap());
     #if QT_CONFIG(printdialog)
         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());
         }
     #endif
     }

     void ImageViewer::copy()
     {
     #ifndef QT_NO_CLIPBOARD
         QGuiApplication::clipboard()->setImage(image);
     #endif // !QT_NO_CLIPBOARD
     }

     #ifndef QT_NO_CLIPBOARD
     static QImage clipboardImage()
     {
         if (const QMimeData *mimeData = QGuiApplication::clipboard()->mimeData()) {
             if (mimeData->hasImage()) {
                 const QImage image = qvariant_cast<QImage>(mimeData->imageData());
                 if (!image.isNull())
                     return image;
             }
         }
         return QImage();
     }
     #endif // !QT_NO_CLIPBOARD

     void ImageViewer::paste()
     {
     #ifndef QT_NO_CLIPBOARD
         const QImage newImage = clipboardImage();
         if (newImage.isNull()) {
             statusBar()->showMessage(tr("No image in clipboard"));
         } else {
             setImage(newImage);
             setWindowFilePath(QString());
             const QString message = tr("Obtained image from clipboard, %1x%2, Depth: %3")
                 .arg(newImage.width()).arg(newImage.height()).arg(newImage.depth());
             statusBar()->showMessage(message);
         }
     #endif // !QT_NO_CLIPBOARD
     }

     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)
             normalSize();
         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()
     {
         QMenu *fileMenu = menuBar()->addMenu(tr("&File"));

         QAction *openAct = fileMenu->addAction(tr("&Open..."), this, &ImageViewer::open);
         openAct->setShortcut(QKeySequence::Open);

         saveAsAct = fileMenu->addAction(tr("&Save As..."), this, &ImageViewer::saveAs);
         saveAsAct->setEnabled(false);

         printAct = fileMenu->addAction(tr("&Print..."), this, &ImageViewer::print);
         printAct->setShortcut(QKeySequence::Print);
         printAct->setEnabled(false);

         fileMenu->addSeparator();

         QAction *exitAct = fileMenu->addAction(tr("E&xit"), this, &QWidget::close);
         exitAct->setShortcut(tr("Ctrl+Q"));

         QMenu *editMenu = menuBar()->addMenu(tr("&Edit"));

         copyAct = editMenu->addAction(tr("&Copy"), this, &ImageViewer::copy);
         copyAct->setShortcut(QKeySequence::Copy);
         copyAct->setEnabled(false);

         QAction *pasteAct = editMenu->addAction(tr("&Paste"), this, &ImageViewer::paste);
         pasteAct->setShortcut(QKeySequence::Paste);

         QMenu *viewMenu = menuBar()->addMenu(tr("&View"));

         zoomInAct = viewMenu->addAction(tr("Zoom &In (25%)"), this, &ImageViewer::zoomIn);
         zoomInAct->setShortcut(QKeySequence::ZoomIn);
         zoomInAct->setEnabled(false);

         zoomOutAct = viewMenu->addAction(tr("Zoom &Out (25%)"), this, &ImageViewer::zoomOut);
         zoomOutAct->setShortcut(QKeySequence::ZoomOut);
         zoomOutAct->setEnabled(false);

         normalSizeAct = viewMenu->addAction(tr("&Normal Size"), this, &ImageViewer::normalSize);
         normalSizeAct->setShortcut(tr("Ctrl+S"));
         normalSizeAct->setEnabled(false);

         viewMenu->addSeparator();

         fitToWindowAct = viewMenu->addAction(tr("&Fit to Window"), this, &ImageViewer::fitToWindow);
         fitToWindowAct->setEnabled(false);
         fitToWindowAct->setCheckable(true);
         fitToWindowAct->setShortcut(tr("Ctrl+F"));

         QMenu *helpMenu = menuBar()->addMenu(tr("&Help"));

         helpMenu->addAction(tr("&About"), this, &ImageViewer::about);
         helpMenu->addAction(tr("About &Qt"), &QApplication::aboutQt);
     }

     void ImageViewer::updateActions()
     {
         saveAsAct->setEnabled(!image.isNull());
         copyAct->setEnabled(!image.isNull());
         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)));
     }