Significantly improve visual when dragging entries to copy/move

* Fixes #6079

share/translations/keepassxc_en.ts

@@ -3997,6 +3997,13 @@ Error: %1</source>
         <source>Reset to defaults</source>
         <translation type="unfinished"></translation>
     </message>
+    <message numerus="yes">
+        <source>+ %1 entry(s)...</source>
+        <translation type="unfinished">
+            <numerusform></numerusform>
+            <numerusform></numerusform>
+        </translation>
+    </message>
 </context>
 <context>
     <name>ExportDialog</name>

src/gui/entry/EntryView.cpp

@@ -19,12 +19,18 @@
 #include "EntryView.h"
 
 #include <QAccessible>
+#include <QDrag>
+#include <QGuiApplication>
 #include <QHeaderView>
+#include <QListWidget>
 #include <QMenu>
 #include <QPainter>
+#include <QScreen>
 #include <QShortcut>
 #include <QStyledItemDelegate>
+#include <QWindow>
 
+#include "gui/Icons.h"
 #include "gui/SortFilterHideProxyModel.h"
 
 #define ICON_ONLY_SECTION_SIZE 26
@@ -507,6 +513,74 @@ void EntryView::showEvent(QShowEvent* event)
     }
 }
 
+void EntryView::startDrag(Qt::DropActions supportedActions)
+{
+    auto selectedIndexes = selectionModel()->selectedRows(EntryModel::Title);
+    if (selectedIndexes.isEmpty()) {
+        return;
+    }
+
+    // Create a mime data object for the selected rows
+    auto mimeData = m_sortModel->mimeData(selectedIndexes);
+    if (!mimeData) {
+        return;
+    }
+
+    // Create a temporary list widget to display the dragged items
+    int i = 0;
+    QListWidget listWidget;
+    for (auto& index : selectedIndexes) {
+        if (++i > 4) {
+            int remaining = selectedIndexes.size() - i + 1;
+            listWidget.addItem(tr("+ %1 entry(s)...", nullptr, remaining).arg(remaining));
+            break;
+        }
+
+        QIcon icon;
+        icon.addPixmap(m_sortModel->data(index, Qt::DecorationRole).value<QPixmap>());
+
+        auto item = new QListWidgetItem;
+        item->setText(m_sortModel->data(index, Qt::DisplayRole).toString());
+        item->setIcon(icon);
+        listWidget.addItem(item);
+    }
+
+    listWidget.setStyleSheet("QListWidget { background-color: palette(highlight); border: 1px solid palette(dark); "
+                             "padding: 4px; color: palette(highlighted-text); }");
+    auto width = listWidget.sizeHintForColumn(0) + 2 * listWidget.frameWidth();
+    auto height = listWidget.sizeHintForRow(0) * listWidget.count() + 2 * listWidget.frameWidth();
+    listWidget.setFixedWidth(width);
+    listWidget.setFixedHeight(height);
+
+    // Grab the screen pixel ratio where the window resides
+    // TODO: Use direct call to screen() when moving to Qt 6
+#if QT_VERSION >= QT_VERSION_CHECK(5, 10, 0)
+    auto screen = QGuiApplication::screenAt(window()->geometry().center());
+    if (!screen) {
+        screen = QGuiApplication::primaryScreen();
+    }
+#else
+    auto screen = QGuiApplication::primaryScreen();
+    if (windowHandle()) {
+        screen = windowHandle()->screen();
+    }
+#endif
+
+    auto pixelRatio = screen->devicePixelRatio();
+
+    // Render the list widget to a pixmap
+    QPixmap pixmap(QSize(width, height) * pixelRatio);
+    pixmap.fill(Qt::transparent);
+    pixmap.setDevicePixelRatio(pixelRatio);
+    listWidget.render(&pixmap);
+
+    // Create a drag object and start the drag
+    auto drag = new QDrag(this);
+    drag->setMimeData(mimeData);
+    drag->setPixmap(pixmap);
+    drag->exec(supportedActions, defaultDropAction());
+}
+
 bool EntryView::isColumnHidden(int logicalIndex)
 {
     return header()->isSectionHidden(logicalIndex) || header()->sectionSize(logicalIndex) == 0;

src/gui/entry/EntryView.h

@@ -61,6 +61,7 @@ protected:
     void keyPressEvent(QKeyEvent* event) override;
     void focusInEvent(QFocusEvent* event) override;
     void showEvent(QShowEvent* event) override;
+    void startDrag(Qt::DropActions supportedActions) override;
 
 private slots:
     void emitEntryActivated(const QModelIndex& index);