YACReader 10: Add support for using Lanczos algorithm scaling.

CHANGELOG.md

@@ -7,6 +7,7 @@ Version counting is based on semantic versioning (Major.Feature.Patch)
 ### YACReader
 * Add support for continuous scroll mode.
 * Fix the translator.
+* Add Lanczos interpolation for image scaling. You can control the method used via the settings under `Image adjustments`.
 
 ### All GUI Apps
 * Migrate Flow implementation from OpenGL to QRhi. This is a full new implementation with better performance and compatibility with operating systems and hardware.
@@ -131,7 +132,7 @@ Version counting is based on semantic versioning (Major.Feature.Patch)
 
 ### YACReaderLibraryServer
 * Add `rescan-xml-info` command.
-* Improved API to provide better integration with the clients (Android 1.4.0 and iOS 3.29.0). 
+* Improved API to provide better integration with the clients (Android 1.4.0 and iOS 3.29.0).
 
 ### All Apps
 * New universal builds for macos.

CMakeLists.txt

@@ -132,6 +132,7 @@ add_subdirectory(common)
 if(NOT BUILD_SERVER_STANDALONE)
     add_subdirectory(shortcuts_management)
     add_subdirectory(custom_widgets)
+    add_subdirectory(image_processing)
 endif()
 
 add_subdirectory(YACReaderLibrary/server)

YACReader/CMakeLists.txt

@@ -98,6 +98,7 @@ target_link_libraries(YACReader PRIVATE
     custom_widgets_reader
     shortcuts_reader
     cbx_backend
+    image_processing
     QsLog
 )
 

YACReader/configuration.h

@@ -10,6 +10,7 @@
 #include <QDate>
 
 #include "yacreader_global_gui.h"
+#include "resize_image.h"
 
 #define CONF_FILE_PATH "."
 #define SLIDE_ASPECT_RATIO 1.585
@@ -117,6 +118,9 @@ class Configuration : public QObject
 
     MouseMode getMouseMode() { return static_cast<MouseMode>(settings->value(MOUSE_MODE, MouseMode::Normal).toInt()); }
     void setMouseMode(MouseMode mouseMode) { settings->setValue(MOUSE_MODE, static_cast<int>(mouseMode)); }
+
+    ScaleMethod getScalingMethod() { return static_cast<ScaleMethod>(settings->value(SCALING_METHOD, static_cast<int>(ScaleMethod::Lanczos)).toInt()); }
+    void setScalingMethod(ScaleMethod method) { settings->setValue(SCALING_METHOD, static_cast<int>(method)); }
 };
 
 }

YACReader/continuous_page_widget.cpp

@@ -1,6 +1,8 @@
 #include "continuous_page_widget.h"
 #include "continuous_view_model.h"
 #include "render.h"
+#include "resize_image.h"
+#include "configuration.h"
 
 #include <QPainter>
 #include <QPaintEvent>
@@ -77,6 +79,12 @@ QSize ContinuousPageWidget::sizeHint() const
     return QSize(width(), continuousViewModel->totalHeight());
 }
 
+void ContinuousPageWidget::invalidateScaledImageCache()
+{
+    scaledPageCache.invalidateAll();
+    update();
+}
+
 void ContinuousPageWidget::onPageAvailable(int absolutePageIndex)
 {
     if (!render || !continuousViewModel || absolutePageIndex < 0 || absolutePageIndex >= continuousViewModel->numPages()) {
@@ -183,7 +191,8 @@ const QImage *ContinuousPageWidget::scaledImageForPaint(int pageIndex, const QIm
     entry.sourceCacheKey = sourceKey;
     entry.sourceSize = source->size();
     entry.targetSize = targetSize;
-    entry.scaledImage = source->scaled(targetSize, Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
+    entry.scaledImage = scaleImage(*source, targetSize.width(), targetSize.height(),
+                                   Configuration::getConfiguration().getScalingMethod());
     scaledPageCache.pages.insert(pageIndex, std::move(entry));
 
     return &scaledPageCache.pages[pageIndex].scaledImage;

YACReader/continuous_page_widget.h

@@ -28,6 +28,7 @@ class ContinuousPageWidget : public QWidget, protected Themable
 
 public slots:
     void onPageAvailable(int absolutePageIndex);
+    void invalidateScaledImageCache();
 
 protected:
     void paintEvent(QPaintEvent *event) override;

YACReader/main_window_viewer.cpp

@@ -148,7 +148,7 @@ void MainWindowViewer::setupUI()
     connect(optionsDialog, &QDialog::accepted, viewer, &Viewer::updateOptions);
     connect(optionsDialog, &YACReaderOptionsDialog::optionsChanged, this, &MainWindowViewer::reloadOptions);
     connect(optionsDialog, &OptionsDialog::changedFilters, viewer, &Viewer::updateFilters);
-    connect(optionsDialog, &OptionsDialog::changedImageOptions, viewer, &Viewer::updatePage);
+    connect(optionsDialog, &OptionsDialog::changedImageOptions, viewer, &Viewer::onImageOptionsChanged);
 
     optionsDialog->restoreOptions(settings);
     // shortcutsDialog = new ShortcutsDialog(this);

YACReader/options_dialog.cpp

@@ -12,6 +12,7 @@
 #include <QLabel>
 #include <QColorDialog>
 #include <QCheckBox>
+#include <QComboBox>
 #include <QMessageBox>
 #include "theme_manager.h"
 #include "theme_factory.h"
@@ -198,6 +199,23 @@ OptionsDialog::OptionsDialog(QWidget *parent)
     doublePageBoxLayout->addWidget(coverSPCheckBox);
     doublePageBox->setLayout(doublePageBoxLayout);
     layoutImageV->addWidget(doublePageBox);
+
+    auto scalingBox = new QGroupBox(tr("Scaling"));
+    auto scalingLayout = new QHBoxLayout();
+    scalingLayout->addWidget(new QLabel(tr("Scaling method")));
+    scalingMethodCombo = new QComboBox();
+    scalingMethodCombo->addItem(tr("Nearest (fast, low quality)"));
+    scalingMethodCombo->addItem(tr("Bilinear"));
+    scalingMethodCombo->addItem(tr("Lanczos (better quality)"));
+    connect(scalingMethodCombo, &QComboBox::currentIndexChanged, this, [this](int index) {
+        Configuration::getConfiguration().setScalingMethod(static_cast<ScaleMethod>(index));
+        emit changedImageOptions();
+    });
+    scalingLayout->addWidget(scalingMethodCombo);
+    scalingLayout->addStretch();
+    scalingBox->setLayout(scalingLayout);
+    layoutImageV->addWidget(scalingBox);
+
     layoutImageV->addStretch();
 
     // IMAGE ADJUSTMENTS END -----------------------------
@@ -294,6 +312,9 @@ void OptionsDialog::saveOptions()
     }
     Configuration::getConfiguration().setMouseMode(mouseMode);
 
+    Configuration::getConfiguration().setScalingMethod(static_cast<ScaleMethod>(scalingMethodCombo->currentIndex()));
+    emit changedImageOptions();
+
     YACReaderOptionsDialog::saveOptions();
 }
 
@@ -330,6 +351,11 @@ void OptionsDialog::restoreOptions(QSettings *settings)
 #endif
     disableScrollAnimations->setChecked(settings->value(DISABLE_SCROLL_ANIMATION, defaultDisableScrollAnimationsValue).toBool());
 
+    {
+        QSignalBlocker blocker(scalingMethodCombo);
+        scalingMethodCombo->setCurrentIndex(static_cast<int>(Configuration::getConfiguration().getScalingMethod()));
+    }
+
     auto mouseMode = Configuration::getConfiguration().getMouseMode();
 
     switch (mouseMode) {

YACReader/options_dialog.h

@@ -6,6 +6,7 @@
 
 #include <QPointer>
 
+class QComboBox;
 class QDialog;
 class QLabel;
 class QLineEdit;
@@ -62,6 +63,8 @@ class OptionsDialog : public YACReaderOptionsDialog, protected Themable
 
     QColor currentColor;
 
+    QComboBox *scalingMethodCombo;
+
     QRadioButton *normalMouseModeRadioButton;
     QRadioButton *leftRightNavigationMouseModeRadioButton;
     QRadioButton *hotAreasMouseModeRadioButton;

YACReader/viewer.cpp

@@ -1,6 +1,7 @@
 #include "viewer.h"
 #include "continuous_page_widget.h"
 #include "continuous_view_model.h"
+#include "resize_image.h"
 #include "configuration.h"
 #include "magnifying_glass.h"
 #include "goto_flow_widget.h"
@@ -357,6 +358,15 @@ void Viewer::goTo(unsigned int page)
     render->goTo(page);
 }
 
+void Viewer::onImageOptionsChanged()
+{
+    if (continuousScroll) {
+        continuousWidget->invalidateScaledImageCache();
+    } else {
+        updatePage();
+    }
+}
+
 void Viewer::updatePage()
 {
     if (continuousScroll) {
@@ -433,16 +443,17 @@ void Viewer::updateContentSize()
         if (zoom != 100) {
             pagefit.scale(floor(pagefit.width() * zoom / 100.0f), 0, Qt::KeepAspectRatioByExpanding);
         }
-        // apply scaling
+        // apply size to the container
         content->resize(pagefit);
 
-        // TODO: updtateContentSize should only scale the pixmap once
-        if (devicePixelRatioF() > 1) // only in HDPI displays
-        {
-            QPixmap page = currentPage->scaled(content->width() * devicePixelRatioF(), content->height() * devicePixelRatioF(), Qt::KeepAspectRatio, Qt::SmoothTransformation);
-            page.setDevicePixelRatio(devicePixelRatioF());
-            content->setPixmap(page);
-        }
+        // scale the pixmap to physical pixels for crisp rendering on all displays
+        auto dpr = devicePixelRatioF();
+        QPixmap page = scalePixmap(*currentPage,
+                                   qRound(content->width() * dpr),
+                                   qRound(content->height() * dpr),
+                                   Configuration::getConfiguration().getScalingMethod());
+        page.setDevicePixelRatio(dpr);
+        content->setPixmap(page);
 
         emit backgroundChanges();
     }

YACReader/viewer.h

@@ -58,6 +58,7 @@ public slots:
     void goToLastPage();
     void goTo(unsigned int page);
     void updatePage();
+    void onImageOptionsChanged();
     void updateContentSize();
     void updateVerticalScrollBar();
     void updateOptions();

common/yacreader_global_gui.h

@@ -39,6 +39,7 @@
 #define USE_SINGLE_SCROLL_STEP_TO_TURN_PAGE "USE_SINGLE_SCROLL_STEP_TO_TURN_PAGE"
 #define DISABLE_SCROLL_ANIMATION "DISABLE_SCROLL_ANIMATION"
 #define MOUSE_MODE "MOUSE_MODE"
+#define SCALING_METHOD "SCALING_METHOD"
 
 #define FLOW_TYPE_GL "FLOW_TYPE_GL"
 #define Y_POSITION "Y_POSITION"

image_processing/CMakeLists.txt

@@ -0,0 +1,9 @@
+add_library(image_processing STATIC
+    resize_image.h
+    resize_image.cpp
+    lancir.h
+)
+
+target_include_directories(image_processing PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+
+target_link_libraries(image_processing PRIVATE Qt::Gui)