imagewidget.cpp Example File

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 #include "imagewidget.h"

 #include <QtWidgets>

 ImageWidget::ImageWidget(QWidget *parent)
     : QWidget(parent),
     position(0),
     horizontalOffset(0),
     verticalOffset(0),
     rotationAngle(0),
     scaleFactor(1),
     currentStepScaleFactor(1)

 {
     setMinimumSize(QSize(100,100));

     grabGesture(Qt::PanGesture);
     grabGesture(Qt::PinchGesture);
     grabGesture(Qt::SwipeGesture);
 }

 bool ImageWidget::event(QEvent *event)
 {
     if (event->type() == QEvent::Gesture)
         return gestureEvent(static_cast<QGestureEvent*>(event));
     return QWidget::event(event);
 }

 void ImageWidget::paintEvent(QPaintEvent*)
 {
     QPainter p(this);

     float iw = currentImage.width();
     float ih = currentImage.height();
     float wh = height();
     float ww = width();

     p.translate(ww/2, wh/2);
     p.translate(horizontalOffset, verticalOffset);
     p.rotate(rotationAngle);
     p.scale(currentStepScaleFactor * scaleFactor, currentStepScaleFactor * scaleFactor);
     p.translate(-iw/2, -ih/2);
     p.drawImage(0, 0, currentImage);
 }

 void ImageWidget::mouseDoubleClickEvent(QMouseEvent *)
 {
     rotationAngle = 0;
     scaleFactor = 1;
     currentStepScaleFactor = 1;
     verticalOffset = 0;
     horizontalOffset = 0;
     update();
 }

 bool ImageWidget::gestureEvent(QGestureEvent *event)
 {
     if (QGesture *swipe = event->gesture(Qt::SwipeGesture))
         swipeTriggered(static_cast<QSwipeGesture *>(swipe));
     else if (QGesture *pan = event->gesture(Qt::PanGesture))
         panTriggered(static_cast<QPanGesture *>(pan));
     if (QGesture *pinch = event->gesture(Qt::PinchGesture))
         pinchTriggered(static_cast<QPinchGesture *>(pinch));
     return true;
 }

 void ImageWidget::panTriggered(QPanGesture *gesture)
 {
 #ifndef QT_NO_CURSOR
     switch (gesture->state()) {
         case Qt::GestureStarted:
         case Qt::GestureUpdated:
             setCursor(Qt::SizeAllCursor);
             break;
         default:
             setCursor(Qt::ArrowCursor);
     }
 #endif
     QPointF delta = gesture->delta();
     horizontalOffset += delta.x();
     verticalOffset += delta.y();
     update();
 }

 void ImageWidget::pinchTriggered(QPinchGesture *gesture)
 {
     QPinchGesture::ChangeFlags changeFlags = gesture->changeFlags();
     if (changeFlags & QPinchGesture::RotationAngleChanged) {
         qreal value = gesture->property("rotationAngle").toReal();
         qreal lastValue = gesture->property("lastRotationAngle").toReal();
         rotationAngle += value - lastValue;
     }
     if (changeFlags & QPinchGesture::ScaleFactorChanged) {
         qreal value = gesture->property("scaleFactor").toReal();
         currentStepScaleFactor = value;
     }
     if (gesture->state() == Qt::GestureFinished) {
         scaleFactor *= currentStepScaleFactor;
         currentStepScaleFactor = 1;
     }
     update();
 }

 void ImageWidget::swipeTriggered(QSwipeGesture *gesture)
 {
     if (gesture->state() == Qt::GestureFinished) {
         if (gesture->horizontalDirection() == QSwipeGesture::Left
             || gesture->verticalDirection() == QSwipeGesture::Up)
             goPrevImage();
         else
             goNextImage();
         update();
     }
 }

 void ImageWidget::resizeEvent(QResizeEvent*)
 {
     update();
 }

 void ImageWidget::openDirectory(const QString &path)
 {
     this->path = path;
     QDir dir(path);
     QStringList nameFilters;
     nameFilters << "*.jpg" << "*.png";
     files = dir.entryList(nameFilters, QDir::Files|QDir::Readable, QDir::Name);

     position = 0;
     goToImage(0);
     update();
 }

 QImage ImageWidget::loadImage(const QString &fileName)
 {
     QImageReader reader(fileName);
     if (!reader.canRead()) {
         qDebug() << fileName << ": can't load image";
         return QImage();
     }

     QImage image;
     if (!reader.read(&image)) {
         qDebug() << fileName << ": corrupted image";
         return QImage();
     }
     return image;
 }

 void ImageWidget::goNextImage()
 {
     if (files.isEmpty())
         return;

     if (position < files.size()-1) {
         ++position;
         prevImage = currentImage;
         currentImage = nextImage;
         if (position+1 < files.size())
             nextImage = loadImage(path+QLatin1String("/")+files.at(position+1));
         else
             nextImage = QImage();
     }
     update();
 }

 void ImageWidget::goPrevImage()
 {
     if (files.isEmpty())
         return;

     if (position > 0) {
         --position;
         nextImage = currentImage;
         currentImage = prevImage;
         if (position > 0)
             prevImage = loadImage(path+QLatin1String("/")+files.at(position-1));
         else
             prevImage = QImage();
     }
     update();
 }

 void ImageWidget::goToImage(int index)
 {
     if (files.isEmpty())
         return;

     if (index < 0 || index >= files.size()) {
         qDebug() << "goToImage: invalid index: " << index;
         return;
     }

     if (index == position+1) {
         goNextImage();
         return;
     }

     if (position > 0 && index == position-1) {
         goPrevImage();
         return;
     }

     position = index;

     if (index > 0)
         prevImage = loadImage(path+QLatin1String("/")+files.at(position-1));
     else
         prevImage = QImage();
     currentImage = loadImage(path+QLatin1String("/")+files.at(position));
     if (position+1 < files.size())
         nextImage = loadImage(path+QLatin1String("/")+files.at(position+1));
     else
         nextImage = QImage();
     update();
 }