Qt 5.11 | Qt Widgets | Image Gestures Example | imagewidget.cpp Example File

Qt 5.11.3 Reference Documentation

# imagewidget.cpp Example File

gestures/imagegestures/imagewidget.cpp

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      #include "imagewidget.h"

      #include <QtWidgets>

      Q_LOGGING_CATEGORY(lcExample, "qt.examples.imagegestures")

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

      {
          setMinimumSize(QSize(100,100));
      }

      void ImageWidget::grabGestures(const QList<Qt::GestureType> &gestures)
      {
          foreach (Qt::GestureType gesture, gestures)
              grabGesture(gesture);
      }

      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);

          const qreal iw = currentImage.width();
          const qreal ih = currentImage.height();
          const qreal wh = height();
          const qreal 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();
          qCDebug(lcExample) << "reset on mouse double click";
      }

      bool ImageWidget::gestureEvent(QGestureEvent *event)
      {
          qCDebug(lcExample) << "gestureEvent():" << 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();
          qCDebug(lcExample) << "panTriggered():" << gesture;
          horizontalOffset += delta.x();
          verticalOffset += delta.y();
          update();
      }

      void ImageWidget::pinchTriggered(QPinchGesture *gesture)
      {
          QPinchGesture::ChangeFlags changeFlags = gesture->changeFlags();
          if (changeFlags & QPinchGesture::RotationAngleChanged) {
              qreal rotationDelta = gesture->rotationAngle() - gesture->lastRotationAngle();
              rotationAngle += rotationDelta;
              qCDebug(lcExample) << "pinchTriggered(): rotate by" <<
                  rotationDelta << "->" << rotationAngle;
          }
          if (changeFlags & QPinchGesture::ScaleFactorChanged) {
              currentStepScaleFactor = gesture->totalScaleFactor();
              qCDebug(lcExample) << "pinchTriggered(): zoom by" <<
                  gesture->scaleFactor() << "->" << currentStepScaleFactor;
          }
          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) {
                  qCDebug(lcExample) << "swipeTriggered(): swipe to previous";
                  goPrevImage();
              } else {
                  qCDebug(lcExample) << "swipeTriggered(): swipe to next";
                  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);
          reader.setAutoTransform(true);
          qCDebug(lcExample) << "loading" << QDir::toNativeSeparators(fileName) << position << '/' << files.size();
          if (!reader.canRead()) {
              qCWarning(lcExample) << QDir::toNativeSeparators(fileName) << ": can't load image";
              return QImage();
          }

          QImage image;
          if (!reader.read(&image)) {
              qCWarning(lcExample) << QDir::toNativeSeparators(fileName) << ": corrupted image: " << reader.errorString();
              return QImage();
          }
          const QSize maximumSize(2000, 2000); // Reduce in case someone has large photo images.
          if (image.size().width() > maximumSize.width() || image.height() > maximumSize.height())
              image = image.scaled(maximumSize, Qt::KeepAspectRatio, Qt::SmoothTransformation);
          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 + QLatin1Char('/') + 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 + QLatin1Char('/') + files.at(position-1));
              else
                  prevImage = QImage();
          }
          update();
      }

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

          if (index < 0 || index >= files.size()) {
              qCWarning(lcExample) << "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 + QLatin1Char('/') + files.at(position-1));
          else
              prevImage = QImage();
          currentImage = loadImage(path + QLatin1Char('/') + files.at(position));
          if (position+1 < files.size())
              nextImage = loadImage(path + QLatin1Char('/') + files.at(position+1));
          else
              nextImage = QImage();
          update();
      }