chore: clean up mouse drag to resize/move logic a little bit

1. No longer fallback to use move(), since all known platforms
   support startSystemMove(), and it's unlikely going to work
   if it's not supported on a specific platform.
2. Fix titlebar move check missing `window()->`.

This amends a10bbb4e8d

app/mainwindow.cpp

@@ -353,16 +353,14 @@ void MainWindow::leaveEvent(QEvent *event)
 
 void MainWindow::mousePressEvent(QMouseEvent *event)
 {
-    bool optionalMaximized = false;
-    #if defined(Q_OS_WIN)
-        optionalMaximized = isMaximized();
-    #endif
+#if defined(Q_OS_WIN)
+    const bool shouldAcceptDrag = !isMaximized() && !isFullScreen();
+#else
+    const bool shouldAcceptDrag = !isFullScreen();
+#endif
 
-    if (event->buttons() & Qt::LeftButton && !optionalMaximized && !isFullScreen()) {
+    if (event->buttons() & Qt::LeftButton && shouldAcceptDrag) {
         m_clickedOnWindow = true;
-        m_oldMousePos = event->pos();
-//        qDebug() << m_oldMousePos << m_graphicsView->transform().m11()
-//                 << m_graphicsView->transform().m22() << m_graphicsView->matrix().m12();
         event->accept();
     }
 
@@ -372,8 +370,8 @@ void MainWindow::mousePressEvent(QMouseEvent *event)
 void MainWindow::mouseMoveEvent(QMouseEvent *event)
 {
     if (event->buttons() & Qt::LeftButton && m_clickedOnWindow) {
-        if (!window()->windowHandle()->startSystemMove()) {
-            move(event->globalPosition().toPoint() - m_oldMousePos);
+        if (window()->windowHandle()->startSystemMove()) {
+            m_clickedOnWindow = false;
         }
         event->accept();
     }

app/mainwindow.h

@@ -119,7 +119,6 @@ private:
     ActionManager *m_am;
     PlaylistManager *m_pm;
 
-    QPoint m_oldMousePos;
     QPropertyAnimation *m_fadeOutAnimation;
     QPropertyAnimation *m_floatUpAnimation;
     QParallelAnimationGroup *m_exitAnimationGroup;

app/titlebar.cpp

@@ -115,7 +115,6 @@ void TitleBar::mousePressEvent(QMouseEvent *event)
     }
 
     m_dragPending = true;
-    m_moveStartPos = event->pos();
     event->accept();
 }
 
@@ -129,17 +128,18 @@ void TitleBar::mouseMoveEvent(QMouseEvent *event)
         }
     }
 
-    bool optionalMaximized = false;
-    #if defined(Q_OS_WIN)
-        optionalMaximized = isMaximized();
-    #endif
+#if defined(Q_OS_WIN)
+    const bool shouldAcceptDrag = !window()->isMaximized() && !window()->isFullScreen();
+#else
+    const bool shouldAcceptDrag = !window()->isFullScreen();
+#endif
+
+    if (event->buttons() & Qt::LeftButton && m_dragPending && shouldAcceptDrag) {
 
-    if (event->buttons() & Qt::LeftButton && m_dragPending
-        && !window()->isFullScreen() && !optionalMaximized) {
-        
         if (QWindow *wh = window()->windowHandle()) {
-            if (!wh->startSystemMove())
-                window()->move(event->globalPosition().toPoint() - m_moveStartPos);
+            if (wh->startSystemMove()) {
+                m_dragPending = false;
+            }
         }
         event->accept();
     }

app/titlebar.h

@@ -54,7 +54,6 @@ private:
     bool m_closeHovered = false;
     bool m_closePressed = false;
     bool m_dragPending = false;
-    QPoint m_moveStartPos;
 };
 
 #endif // TITLEBAR_H