make cover art window draggable

src/library/dlgcoverartfullsize.cpp

@@ -164,14 +164,38 @@ void DlgCoverArtFullSize::slotCoverInfoSelected(const CoverInfoRelative& coverIn
 }
 
 void DlgCoverArtFullSize::mousePressEvent(QMouseEvent* event) {
-    Q_UNUSED(event);
+    if (!m_pCoverMenu->isVisible() && event->button() == Qt::LeftButton) {
+        m_clickTimer.setSingleShot(true);
+        m_clickTimer.start(500);
+        m_coverPressed = true;
+        m_dragStartPosition = event->globalPos() - frameGeometry().topLeft();
+    }
+}
 
+void DlgCoverArtFullSize::mouseReleaseEvent(QMouseEvent* event) {
+    m_coverPressed = false;
     if (m_pCoverMenu->isVisible()) {
         return;
     }
 
     if (event->button() == Qt::LeftButton && isVisible()) {
-        close();
+        if (m_clickTimer.isActive()) {
+        // short press
+            close();
+        } else {
+        // long press
+            return;
+        }
+        event->accept();
+    }
+}
+
+void DlgCoverArtFullSize::mouseMoveEvent(QMouseEvent* event) {
+    if (m_coverPressed) {
+        move(event->globalPos() - m_dragStartPosition);
+        event->accept();
+    } else {
+        return;
     }
 }
 

src/library/dlgcoverartfullsize.h

@@ -2,6 +2,8 @@
 #define DLGCOVERARTFULLSIZE_H
 
 #include <QDialog>
+#include <QTimer>
+#include <QPoint>
 
 #include "library/ui_dlgcoverartfullsize.h"
 #include "library/coverart.h"
@@ -18,7 +20,9 @@ class DlgCoverArtFullSize
     virtual ~DlgCoverArtFullSize();
 
     void init(TrackPointer pTrack);
-    void mousePressEvent(QMouseEvent* /* unused */) override;
+    void mousePressEvent(QMouseEvent* event) override;
+    void mouseReleaseEvent(QMouseEvent* ) override;
+    void mouseMoveEvent(QMouseEvent* ) override;
     void resizeEvent(QResizeEvent* event) override;
     void wheelEvent(QWheelEvent* event) override;
 
@@ -38,6 +42,9 @@ class DlgCoverArtFullSize
     TrackPointer m_pLoadedTrack;
     BaseTrackPlayer* m_pPlayer;
     WCoverArtMenu* m_pCoverMenu;
+    QTimer m_clickTimer;
+    QPoint m_dragStartPosition;
+    bool m_coverPressed;
 };
 
 #endif // DLGCOVERARTFULLSIZE_H