QWidget(parent),

ui(new Ui::ImageViewer),

m_image_size(0, 0),

m_pan_mode{false}

{

ui->setupUi(this);

ui->scrollArea->viewport()->installEventFilter(this);

connect(ui->buttonOriginalSize, &QToolButton::clicked, this, [this]{ scaleImage(100); });

ui->labelView->addAction(ui->actionPrintImage);

{

auto widget_size = ui->scrollArea->viewport()->size();

m_image_size = image.size();

ui->labelView->setMaximumSize(m_image_size.scaled(widget_size, Qt::KeepAspectRatio));

ui->labelView->setPixmap(QPixmap::fromImage(image));

// If the image is larger than the viewport scale it to fit the viewport.

// If the image is smaller than the viewport show it in its original size.

if(!isQSizeCovered(m_image_size))

ui->buttonFitToWindow->setChecked(true);

else

scaleImage(100);

{

auto widget_size = ui->scrollArea->viewport()->size();

return widget_size.width() >= rect.width() && widget_size.height() >= rect.height();

auto e_type = e->type();

if (e_type == QEvent::Wheel) {

auto *wheel_event = static_cast<QWheelEvent*>(e);

auto step = ui->sliderScale->pageStep();

if (wheel_event->angleDelta().y() < 0) {

step = -step;

}

scaleImage(ui->sliderScale->value() + step);

e->accept();

return true;

}

if (ui->buttonFitToWindow->isChecked()) {

if (e_type == QEvent::Resize)

scaleToFitWindow(true);

} else if (e_type >= QEvent::MouseButtonPress && e_type <= QEvent::MouseMove) {

auto *mouse_event = static_cast<QMouseEvent*>(e);

if (e_type == QEvent::MouseButtonPress && mouse_event->button() == Qt::LeftButton &&

!isQSizeCovered(ui->labelView->size())) {

m_mouse_down = mouse_event->globalPos();

m_pan_mode = true;

ui->scrollArea->setCursor(Qt::ClosedHandCursor);

} else if (e_type == QEvent::MouseMove && m_pan_mode) {

auto dx = mouse_event->globalX() - m_mouse_down.x();

auto dy = mouse_event->globalY() - m_mouse_down.y();

m_mouse_down = mouse_event->globalPos();

if (dx != 0) {

ui->scrollArea->horizontalScrollBar()->setValue(ui->scrollArea->horizontalScrollBar()->value() - dx);

}

if (dy != 0) {

ui->scrollArea->verticalScrollBar()->setValue(ui->scrollArea->verticalScrollBar()->value() - dy);

}

} else if (e_type == QEvent::MouseButtonRelease && mouse_event->button() == Qt::LeftButton) {

m_pan_mode = false;

ui->scrollArea->setCursor(Qt::ArrowCursor);

}

}

return false;

{

QPrinter printer;

QPrintPreviewDialog dialog(&printer);

connect(&dialog, &QPrintPreviewDialog::paintRequested, &dialog, [&](QPrinter* previewPrinter) {

QPainter painter(previewPrinter);

QRect rect = painter.viewport();

#if QT_VERSION < QT_VERSION_CHECK(5, 15, 0)

QPixmap pixmap = *ui->labelView->pixmap();

#else

QPixmap pixmap = ui->labelView->pixmap(Qt::ReturnByValue);

#endif

QSize size = pixmap.size();

size.scale(rect.size(), Qt::KeepAspectRatio);

painter.setViewport(rect.x(), rect.y(), size.width(), size.height());

painter.setWindow(pixmap.rect());

painter.drawPixmap(0, 0, pixmap);

});

dialog.exec();

{

// Enable/disable the automatic resizing of the label inside the scrollbar

ui->scrollArea->setWidgetResizable(enabled);

// When disabling the fit to window scaling, revert back to the original image size

if(!enabled) {

scaleImage(100);

} else {

ui->labelView->setMaximumSize(m_image_size.scaled(ui->scrollArea->viewport()->size(), Qt::KeepAspectRatio));

setSliderValueWithoutSignal(static_cast<int>(ui->labelView->maximumWidth() / static_cast<double>(m_image_size.width()) * 100));

}

{

if (ui->buttonFitToWindow->isChecked()) {

ui->buttonFitToWindow->blockSignals(true);

ui->scrollArea->setWidgetResizable(false);

ui->buttonFitToWindow->setChecked(false);

ui->buttonFitToWindow->blockSignals(false);

}

{

ui->sliderScale->blockSignals(true);

ui->sliderScale->setValue(value);

ui->sliderScale->blockSignals(false);

{

// Clamp scale to the sliderScale min/max

scale = std::min(ui->sliderScale->maximum(), std::max(ui->sliderScale->minimum(), scale));

// Make sure the slider is updated when this is called programmatically

setSliderValueWithoutSignal(scale);

// Uncheck the fit to window button

setNoFitWithoutSignal();

// Update our scale factor

auto scale_factor = scale / 100.0;

// Resize the image

auto max_size_old = ui->labelView->maximumSize();

ui->labelView->setMaximumSize(m_image_size * scale_factor);

ui->labelView->resize(ui->labelView->maximumSize());

auto factor_change = ui->labelView->maximumWidth() / static_cast<double>(max_size_old.width());

// Fix scroll bars to zoom into center of viewport instead of the upper left corner

const auto adjust_scrollbar = [](QScrollBar* scroll_bar, qreal factor) {

scroll_bar->setValue(static_cast<int>(factor * scroll_bar->value() + ((factor - 1) * scroll_bar->pageStep() / 2)));

};

adjust_scrollbar(ui->scrollArea->horizontalScrollBar(), factor_change);

adjust_scrollbar(ui->scrollArea->verticalScrollBar(), factor_change);