Fix fullscreen composition artifact

Author: Marcelo Jorquera

src/apps/mplayerc/MainFrm.cpp

@@ -11096,6 +11096,17 @@ void CMainFrame::ToggleFullscreen(bool fToNearest, bool fSwitchScreenResWhenHasT
 
 	m_bFullScreen = !m_bFullScreen;
 
+	// Keep the main HWND logically visible so the normal MFC/child layout runs
+	// during the fullscreen resize, but temporarily remove it from DWM
+	// presentation while its frame and geometry are being rewritten.  Cloaking
+	// is Windows 8+, so Windows 7 and earlier retain the original code path.
+	bool bCloakedForFullscreenTransition = false;
+	if (SysVersion::IsWin8orLater() && IsWindowVisible()) {
+		const BOOL bCloak = TRUE;
+		bCloakedForFullscreenTransition = SUCCEEDED(DwmSetWindowAttribute(
+			m_hWnd, DWMWA_CLOAK, &bCloak, sizeof(bCloak)));
+	}
+
 	ModifyStyle(dwRemove, dwAdd, SWP_NOZORDER);
 
 	static bool bChangeMonitor = false;
@@ -11209,6 +11220,17 @@ void CMainFrame::ToggleFullscreen(bool fToNearest, bool fSwitchScreenResWhenHasT
 	m_bFullScreenChangingMode = false;
 	MoveVideoWindow();
 
+	// Reveal only after the final top-level and video-child geometry has been
+	// processed. Wait for the compositor to reach the transition's final
+	// presentation point first; unlike a forced RedrawWindow this does not
+	// synchronously repaint a stale pre-WM_SIZE child surface.
+	if (bCloakedForFullscreenTransition) {
+		DwmFlush();
+
+		const BOOL bCloak = FALSE;
+		DwmSetWindowAttribute(m_hWnd, DWMWA_CLOAK, &bCloak, sizeof(bCloak));
+	}
+
 	if (bChangeMonitor && (!m_bToggleShader || !m_bToggleShaderScreenSpace)) { // Enabled shader ...
 		SetShaders();
 	}