From f2bf43a8bc39530e5c7d0cbc1d06bd400bb540b1 Mon Sep 17 00:00:00 2001
From: edde746 <86283021+edde746@users.noreply.github.com>
Date: Sun, 23 Aug 2026 10:57:42 +0200
Subject: [PATCH] fix(windows): restore window placement onto a live monitor
 without a blank flash

The remembered window placement restored invisible when its monitor was
gone (undocked laptop, powered-off TV), briefly flashed a blank window at
the restored spot before the first Flutter frame, and could lose the
maximized state: the exit path hides the window before a multi-second
teardown, so a debounced save landing in that gap recorded SW_HIDE, and a
window closed while minimized-from-maximized restored as a normal window.

Validate the saved rect against current monitors and keep only the size on
a miss, apply the placement with SW_HIDE so the first-frame callback stays
the single show, skip persisting while the window is hidden, and honor
WPF_RESTORETOMAXIMIZED when deciding to relaunch maximized.
---
 windows/runner/flutter_window.cpp | 43 ++++++++++++++++++++++++++-----
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/windows/runner/flutter_window.cpp b/windows/runner/flutter_window.cpp
index 519650177..05cd9799e 100644
--- a/windows/runner/flutter_window.cpp
+++ b/windows/runner/flutter_window.cpp
@@ -35,12 +35,19 @@ static void WriteWindowPlacement(const WINDOWPLACEMENT& wp) {
 }
 
 static void SaveWindowPlacement(HWND hwnd) {
+  // Never persist a hidden window: the exit path hides the window before its
+  // multi-second teardown, and a save landing in that gap would record
+  // SW_HIDE over the user's real show state.
+  if (!IsWindowVisible(hwnd)) return;
   WINDOWPLACEMENT wp{};
   wp.length = sizeof(wp);
   if (!GetWindowPlacement(hwnd, &wp)) return;
   WriteWindowPlacement(wp);
 }
 
+// Loads the saved WINDOWPLACEMENT and applies it while keeping the window
+// hidden; the first-frame callback in OnCreate performs the single show.
+// Returns whether the window should be shown maximized.
 static bool LoadWindowPlacement(HWND hwnd) {
   HKEY hKey;
   if (RegOpenKeyExW(HKEY_CURRENT_USER, kWindowPlacementKey, 0, KEY_READ, &hKey) != ERROR_SUCCESS) return false;
@@ -53,10 +60,34 @@ static bool LoadWindowPlacement(HWND hwnd) {
   if (RegQueryValueExW(hKey, kWindowPlacementValue, nullptr, nullptr, reinterpret_cast<BYTE*>(&wp), &size) ==
           ERROR_SUCCESS &&
       size == sizeof(wp)) {
-    // Prevent restoring as minimized
-    if (wp.showCmd == SW_SHOWMINIMIZED) wp.showCmd = SW_SHOWNORMAL;
+    // A window minimized away from the maximized state stores SW_SHOWMINIMIZED
+    // plus WPF_RESTORETOMAXIMIZED; both spellings mean "maximized" on relaunch.
+    wasMaximized = wp.showCmd == SW_SHOWMAXIMIZED || (wp.flags & WPF_RESTORETOMAXIMIZED) != 0;
+
+    // The saved monitor may be gone (undocked laptop, powered-off TV).
+    // rcNormalPosition is in workspace coordinates — screen coordinates offset
+    // by the primary work area — so convert before testing against monitors.
+    // On a miss, keep the size but fall back to the default creation position
+    // so the window never restores invisible.
+    RECT workArea{};
+    SystemParametersInfoW(SPI_GETWORKAREA, 0, &workArea, 0);
+    RECT screenRect = wp.rcNormalPosition;
+    OffsetRect(&screenRect, workArea.left, workArea.top);
+    if (MonitorFromRect(&screenRect, MONITOR_DEFAULTTONULL) == nullptr) {
+      RECT current{};
+      GetWindowRect(hwnd, &current);
+      const LONG width = wp.rcNormalPosition.right - wp.rcNormalPosition.left;
+      const LONG height = wp.rcNormalPosition.bottom - wp.rcNormalPosition.top;
+      wp.rcNormalPosition.left = current.left - workArea.left;
+      wp.rcNormalPosition.top = current.top - workArea.top;
+      wp.rcNormalPosition.right = wp.rcNormalPosition.left + width;
+      wp.rcNormalPosition.bottom = wp.rcNormalPosition.top + height;
+    }
+
+    // Apply hidden. A visible showCmd here would display a blank window at
+    // the restored spot before Flutter has rendered anything.
+    wp.showCmd = SW_HIDE;
     SetWindowPlacement(hwnd, &wp);
-    wasMaximized = (wp.showCmd == SW_SHOWMAXIMIZED);
   }
 
   RegCloseKey(hKey);
@@ -155,9 +186,9 @@ FlutterWindow::MessageHandler(HWND hwnd, UINT const message, WPARAM const wparam
       flutter_controller_->engine()->ReloadSystemFonts();
       break;
     case WM_WINDOWPOSCHANGED:
-      // Don't persist placement while in fullscreen or mid-toggle — the rect
-      // would overwrite the user's real window position.
-      if (!is_fullscreen_ && !g_suppressPlacementSave) {
+      // Don't persist placement while fullscreen, mid-toggle, or hidden — the
+      // rect would overwrite the user's real window position or show state.
+      if (!is_fullscreen_ && !g_suppressPlacementSave && IsWindowVisible(hwnd)) {
         DebounceSaveWindowPlacement(hwnd);
       }
       break;