Change flags / attributes when changing window frame.

Telegram/SourceFiles/window/main_window.cpp

@@ -363,6 +363,21 @@ void MainWindow::refreshTitleWidget() {
 		_title->init();
 		_titleShadow.destroy();
 	}
+
+#ifdef Q_OS_LINUX
+	// setWindowFlag calls setParent(parentWidget(), newFlags), which
+	// always calls hide() explicitly, we have to show() the window back.
+	const auto hidden = isHidden();
+	const auto withShadow = hasShadow();
+	setWindowFlag(Qt::NoDropShadowWindowHint, withShadow);
+	setAttribute(Qt::WA_OpaquePaintEvent, !withShadow);
+	if (!hidden) {
+		base::call_delayed(
+			kShowAfterWindowFlagChangeDelay,
+			this,
+			[=] { show(); });
+	}
+#endif // Q_OS_LINUX
 }
 
 void MainWindow::updateMinimumSize() {

Telegram/SourceFiles/window/window_title_qt.cpp

@@ -24,13 +24,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 namespace Window {
 namespace {
 
-// If we toggle frameless window hint in maximized window, and
-// show it back too quickly, the mouse position inside the window
-// won't be correct (from Qt-s point of view) until we Alt-Tab from
-// that window. If we show the window back with this delay it works.
-constexpr auto kShowAfterFramelessToggleDelay = crl::time(1000);
-
-style::margins ShadowExtents() {
+[[nodiscard]] style::margins ShadowExtents() {
 	return st::callShadow.extend;
 }
 

Telegram/SourceFiles/window/window_title_qt.h

@@ -22,6 +22,12 @@ class PlainShadow;
 
 namespace Window {
 
+// If we toggle frameless window hint in maximized window, and
+// show it back too quickly, the mouse position inside the window
+// won't be correct (from Qt-s point of view) until we Alt-Tab from
+// that window. If we show the window back with this delay it works.
+inline constexpr auto kShowAfterWindowFlagChangeDelay = crl::time(1000);
+
 class TitleWidgetQt : public TitleWidget {
 public:
 	TitleWidgetQt(QWidget *parent);