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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) {
             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()
     {
         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)));
     }