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

@@ -229,15 +229,22 @@ void MainWindow::adjustWindowSizeBySceneRect()
             // we can show the picture by increase the window size.
             QSize finalSize = (screenSize.expandedTo(sceneSizeWithMargins) == screenSize) ?
                               sceneSizeWithMargins : screenSize;
+
+            // to avoid the window appearing maximized while not being actually maximized
+            // which is common when viewing screenshots of the same screen size
+            if (finalSize == screenSize) {
+                showMaximized();
+            } else {
                 // We have a very reasonable sizeHint() value ;P
                 this->resize(finalSize.expandedTo(this->sizeHint()));
+                centerWindow();
+            }
 
             // We're sure the window can display the whole thing with 1:1 scale.
             // The old window size may cause fitInView call from resize() and the
             // above resize() call won't reset the scale back to 1:1, so we
             // just call resetScale() here to ensure the thing is no longer scaled.
             m_graphicsView->resetScale();
-            centerWindow();
         } else {
             // toggle maximum
             showMaximized();
@@ -346,11 +353,14 @@ void MainWindow::leaveEvent(QEvent *event)
 
 void MainWindow::mousePressEvent(QMouseEvent *event)
 {
-    if (event->buttons() & Qt::LeftButton && !isMaximized()) {
+#if defined(Q_OS_WIN)
+    const bool shouldAcceptDrag = !isMaximized() && !isFullScreen();
+#else
+    const bool shouldAcceptDrag = !isFullScreen();
+#endif
+
+    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();
     }
 
@@ -359,9 +369,9 @@ void MainWindow::mousePressEvent(QMouseEvent *event)
 
 void MainWindow::mouseMoveEvent(QMouseEvent *event)
 {
-    if (event->buttons() & Qt::LeftButton && m_clickedOnWindow && !isMaximized() && !isFullScreen()) {
-        if (!window()->windowHandle()->startSystemMove()) {
-            move(event->globalPosition().toPoint() - m_oldMousePos);
+    if (event->buttons() & Qt::LeftButton && m_clickedOnWindow) {
+        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();
 }
 
@@ -129,11 +128,18 @@ void TitleBar::mouseMoveEvent(QMouseEvent *event)
         }
     }
 
-    if (event->buttons() & Qt::LeftButton && m_dragPending
-        && !window()->isMaximized() && !window()->isFullScreen()) {
+#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 (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