Image Gestures Example

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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();
}