views: Use scene devicePixelRatio rather than qApp

When possible, use the devicePixelRatio from the scene which on Wayland
unlike the QApplication will properly support fractional scaling.

A KItemViewsUtils class is introduced that can be reused elsewhere.

src/CMakeLists.txt

@@ -83,6 +83,7 @@ target_sources(dolphinprivate PRIVATE
     kitemviews/private/kitemlistsmoothscroller.cpp
     kitemviews/private/kitemlistviewanimation.cpp
     kitemviews/private/kitemlistviewlayouter.cpp
+    kitemviews/private/kitemviewsutils.cpp
     kitemviews/private/kpixmapmodifier.cpp
     settings/applyviewpropsjob.cpp
     settings/viewmodes/viewmodesettings.cpp

src/kitemviews/kfileitemlistview.cpp

@@ -9,6 +9,7 @@
 #include "kfileitemlistwidget.h"
 #include "kfileitemmodel.h"
 #include "kfileitemmodelrolesupdater.h"
+#include "private/kitemviewsutils.h"
 #include "private/kpixmapmodifier.h"
 
 #include <KIconLoader>
@@ -157,7 +158,7 @@ QPixmap KFileItemListView::createDragPixmap(const KItemSet &indexes) const
         yCount = xCount;
     }
 
-    const qreal dpr = scene()->views()[0]->devicePixelRatio();
+    const qreal dpr = KItemViewsUtils::devicePixelRatio(this);
     // Draw the selected items into the grid cells.
     QPixmap dragPixmap(QSize(xCount * size + xCount, yCount * size + yCount) * dpr);
     dragPixmap.setDevicePixelRatio(dpr);
@@ -255,6 +256,7 @@ void KFileItemListView::onModelChanged(KItemModelBase *current, KItemModelBase *
     if (current) {
         m_modelRolesUpdater = new KFileItemModelRolesUpdater(static_cast<KFileItemModel *>(current), this);
         m_modelRolesUpdater->setIconSize(availableIconSize());
+        m_modelRolesUpdater->setDevicePixelRatio(KItemViewsUtils::devicePixelRatio(this));
 
         applyRolesToModel();
     }
@@ -414,6 +416,7 @@ void KFileItemListView::updateIconSize()
     }
 
     m_modelRolesUpdater->setIconSize(availableIconSize());
+    m_modelRolesUpdater->setDevicePixelRatio(KItemViewsUtils::devicePixelRatio(this));
 
     // Update the visible index range (which has most likely changed after the
     // icon size change) before unpausing m_modelRolesUpdater.

src/kitemviews/kstandarditemlistwidget.cpp

@@ -10,6 +10,7 @@
 #include "kfileitemmodel.h"
 #include "private/kfileitemclipboard.h"
 #include "private/kitemlistroleeditor.h"
+#include "private/kitemviewsutils.h"
 #include "private/kpixmapmodifier.h"
 
 #include <KIconEffect>
@@ -965,6 +966,7 @@ void KStandardItemListWidget::updatePixmapCache()
     const bool iconOnTop = (m_layout == IconsLayout);
     const KItemListStyleOption &option = styleOption();
     const qreal padding = option.padding;
+    const qreal dpr = KItemViewsUtils::devicePixelRatio(this);
 
     const int widgetIconSize = iconSize();
     const int maxIconWidth = iconOnTop ? widgetSize.width() - 2 * padding : widgetIconSize;
@@ -1025,7 +1027,7 @@ void KStandardItemListWidget::updatePixmapCache()
         } else if (m_pixmap.width() / m_pixmap.devicePixelRatio() != maxIconWidth || m_pixmap.height() / m_pixmap.devicePixelRatio() != maxIconHeight) {
             // A custom pixmap has been applied. Assure that the pixmap
             // is scaled to the maximum available size.
-            KPixmapModifier::scale(m_pixmap, QSize(maxIconWidth, maxIconHeight) * qApp->devicePixelRatio());
+            KPixmapModifier::scale(m_pixmap, QSize(maxIconWidth, maxIconHeight) * dpr);
         }
 
         if (m_pixmap.isNull()) {
@@ -1073,8 +1075,8 @@ void KStandardItemListWidget::updatePixmapCache()
     const int maxScaledIconHeight = scaledIconSize;
 
     m_scaledPixmapSize = m_pixmap.size();
-    m_scaledPixmapSize.scale(maxScaledIconWidth * qApp->devicePixelRatio(), maxScaledIconHeight * qApp->devicePixelRatio(), Qt::KeepAspectRatio);
+    m_scaledPixmapSize.scale(maxScaledIconWidth * dpr, maxScaledIconHeight * dpr, Qt::KeepAspectRatio);
-    m_scaledPixmapSize = m_scaledPixmapSize / qApp->devicePixelRatio();
+    m_scaledPixmapSize = m_scaledPixmapSize / dpr;
 
     if (iconOnTop) {
         // Center horizontally and align on bottom within the icon-area
@@ -1171,7 +1173,7 @@ void KStandardItemListWidget::updateTextsCache()
         if (ratingSize.width() > availableWidth) {
             ratingSize.rwidth() = availableWidth;
         }
-        const qreal dpr = qApp->devicePixelRatio();
+        const qreal dpr = KItemViewsUtils::devicePixelRatio(this);
         m_rating = QPixmap(ratingSize.toSize() * dpr);
         m_rating.setDevicePixelRatio(dpr);
         m_rating.fill(Qt::transparent);
@@ -1473,9 +1475,10 @@ void KStandardItemListWidget::updateAdditionalInfoTextColor()
 void KStandardItemListWidget::drawPixmap(QPainter *painter, const QPixmap &pixmap)
 {
     if (m_scaledPixmapSize != pixmap.size() / pixmap.devicePixelRatio()) {
+        const qreal dpr = KItemViewsUtils::devicePixelRatio(this);
         QPixmap scaledPixmap = pixmap;
-        KPixmapModifier::scale(scaledPixmap, m_scaledPixmapSize * qApp->devicePixelRatio());
+        KPixmapModifier::scale(scaledPixmap, m_scaledPixmapSize * dpr);
-        scaledPixmap.setDevicePixelRatio(qApp->devicePixelRatio());
+        scaledPixmap.setDevicePixelRatio(dpr);
         painter->drawPixmap(m_pixmapPos, scaledPixmap);
 
 #ifdef KSTANDARDITEMLISTWIDGET_DEBUG
@@ -1559,10 +1562,7 @@ void KStandardItemListWidget::closeRoleEditor()
 QPixmap KStandardItemListWidget::pixmapForIcon(const QString &name, const QStringList &overlays, int size, QIcon::Mode mode) const
 {
     static const QIcon fallbackIcon = QIcon::fromTheme(QStringLiteral("unknown"));
-    qreal dpr = qApp->devicePixelRatio();
+    const qreal dpr = KItemViewsUtils::devicePixelRatio(this);
-    if (scene() && !scene()->views().isEmpty()) {
-        dpr = scene()->views().constFirst()->devicePixelRatioF();
-    }
 
     size *= dpr;
 

src/kitemviews/private/kitemviewsutils.cpp

@@ -0,0 +1,23 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Kai Uwe Broulik <kde@broulik.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "kitemviewsutils.h"
+
+#include <QApplication>
+#include <QGraphicsItem>
+#include <QGraphicsScene>
+#include <QGraphicsView>
+
+qreal KItemViewsUtils::devicePixelRatio(const QGraphicsItem *item)
+{
+    qreal dpr = qApp->devicePixelRatio();
+    if (item->scene()) {
+        if (const auto views = item->scene()->views(); !views.isEmpty()) {
+            dpr = views.first()->devicePixelRatioF();
+        }
+    }
+    return dpr;
+}

src/kitemviews/private/kitemviewsutils.h

@@ -0,0 +1,20 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Kai Uwe Broulik <kde@broulik.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef KITEMVIEWSUTILS_H
+#define KITEMVIEWSUTILS_H
+
+#include <qtypes.h>
+
+class QGraphicsItem;
+
+class KItemViewsUtils
+{
+public:
+    static qreal devicePixelRatio(const QGraphicsItem *item);
+};
+
+#endif // KITEMVIEWSUTILS_H

src/views/dolphinfileitemlistwidget.cpp

@@ -5,6 +5,7 @@
  */
 
 #include "dolphinfileitemlistwidget.h"
+#include "../kitemviews/private/kitemviewsutils.h"
 
 #include "dolphindebug.h"
 
@@ -77,7 +78,7 @@ void DolphinFileItemListWidget::refreshCache()
     setTextColor(color);
 }
 
-QPixmap DolphinFileItemListWidget::overlayForState(KVersionControlPlugin::ItemVersion version, int size)
+QPixmap DolphinFileItemListWidget::overlayForState(KVersionControlPlugin::ItemVersion version, int size) const
 {
     int overlayHeight = KIconLoader::SizeSmall;
     if (size >= KIconLoader::SizeEnormous) {
@@ -122,7 +123,8 @@ QPixmap DolphinFileItemListWidget::overlayForState(KVersionControlPlugin::ItemVe
         break;
     }
 
-    return QIcon::fromTheme(iconName).pixmap(QSize(overlayHeight, overlayHeight));
+    const qreal dpr = KItemViewsUtils::devicePixelRatio(this);
+    return QIcon::fromTheme(iconName).pixmap(QSize(overlayHeight, overlayHeight), dpr);
 }
 
 #include "moc_dolphinfileitemlistwidget.cpp"

src/views/dolphinfileitemlistwidget.h

@@ -29,7 +29,7 @@ protected:
     void refreshCache() override;
 
 private:
-    static QPixmap overlayForState(KVersionControlPlugin::ItemVersion version, int size);
+    QPixmap overlayForState(KVersionControlPlugin::ItemVersion version, int size) const;
 };
 
 #endif