From 02dc57bd5504e731260223950ee58f840bd3c166 Mon Sep 17 00:00:00 2001
From: edde746 <86283021+edde746@users.noreply.github.com>
Date: Sun, 6 Sep 2026 01:28:12 +0200
Subject: [PATCH] fix(windows): restore snapped windows in their monitor
 workspace

Snapped windows on secondary displays can restore with the primary monitor's taskbar offset. Normalize the saved screen rect using its own monitor inset and reverse that conversion when checking restored placement. Keep missing-monitor fallback coordinates in the creation monitor's workspace.

The Win32 API model changes four-cycle drift from plus or minus 192 pixels to zero. Single-monitor native fullscreen and quit-fullscreen/relaunch roundtrips passed; physical multi-monitor and mixed-DPI verification remains unavailable in the disconnected session.
---
 windows/runner/flutter_window.cpp | 41 +++++++++++++++++++------------
 1 file changed, 25 insertions(+), 16 deletions(-)

diff --git a/windows/runner/flutter_window.cpp b/windows/runner/flutter_window.cpp
index 215bd99eb..6727bcce7 100644
--- a/windows/runner/flutter_window.cpp
+++ b/windows/runner/flutter_window.cpp
@@ -50,14 +50,14 @@ static bool QueryWindowPlacement(HWND hwnd, WINDOWPLACEMENT* wp) {
       reinterpret_cast<IsWindowArrangedFn>(GetProcAddress(GetModuleHandleW(L"user32.dll"), "IsWindowArranged"));
   if (!is_window_arranged || IsIconic(hwnd) || IsZoomed(hwnd) || !is_window_arranged(hwnd)) return true;
 
-  // rcNormalPosition is in workspace coordinates (offset by the primary work
-  // area) while GetWindowRect is in screen coordinates; LoadWindowPlacement
-  // applies the inverse offset.
+  // rcNormalPosition uses the window monitor's workspace inset, not the
+  // primary work area's screen origin. LoadWindowPlacement reverses this.
   RECT rect{};
   if (!GetWindowRect(hwnd, &rect)) return true;
-  RECT workArea{};
-  SystemParametersInfoW(SPI_GETWORKAREA, 0, &workArea, 0);
-  OffsetRect(&rect, -workArea.left, -workArea.top);
+  MONITORINFO mi{};
+  mi.cbSize = sizeof(mi);
+  if (!GetMonitorInfoW(MonitorFromWindow(hwnd, MONITOR_DEFAULTTONEAREST), &mi)) return true;
+  OffsetRect(&rect, mi.rcMonitor.left - mi.rcWork.left, mi.rcMonitor.top - mi.rcWork.top);
   wp->rcNormalPosition = rect;
   return true;
 }
@@ -92,21 +92,30 @@ static bool LoadWindowPlacement(HWND hwnd) {
     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.
+    // Resolve the saved rect's monitor before reversing its workspace inset.
     // 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);
+    MONITORINFO mi{};
+    mi.cbSize = sizeof(mi);
+    bool on_screen = false;
+    if (GetMonitorInfoW(MonitorFromRect(&screenRect, MONITOR_DEFAULTTONEAREST), &mi)) {
+      OffsetRect(&screenRect, mi.rcWork.left - mi.rcMonitor.left, mi.rcWork.top - mi.rcMonitor.top);
+      on_screen = MonitorFromRect(&screenRect, MONITOR_DEFAULTTONULL) != nullptr;
+    }
+    if (!on_screen) {
+      // GetWindowPlacement already expresses the creation rect in its own
+      // monitor's workspace, including when the default monitor has an inset.
+      WINDOWPLACEMENT current{};
+      current.length = sizeof(current);
+      if (!GetWindowPlacement(hwnd, &current)) {
+        RegCloseKey(hKey);
+        return false;
+      }
       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.left = current.rcNormalPosition.left;
+      wp.rcNormalPosition.top = current.rcNormalPosition.top;
       wp.rcNormalPosition.right = wp.rcNormalPosition.left + width;
       wp.rcNormalPosition.bottom = wp.rcNormalPosition.top + height;
     }