Almost working. Doesn't apply on my small monitor running at 150% scaling.

src/modules/fancyzones/editor/FancyZonesEditor/Models/LayoutModel.cs

@@ -186,14 +186,12 @@ namespace FancyZonesEditor.Models
             // Scale all the zones to the DPI and then pack them up to be marshalled.
             int zoneCount = zones.Length;
             var zoneArray = new int[zoneCount * 4];
-            var graphics = System.Drawing.Graphics.FromHwnd(IntPtr.Zero);
-            float dpi = graphics.DpiX / 96;
             for (int i = 0; i < zones.Length; i++)
             {
-                var left = (int)(zones[i].X * dpi);
+                var left = (int)(zones[i].X * Settings.Dpi);
-                var top = (int)(zones[i].Y * dpi);
+                var top = (int)(zones[i].Y * Settings.Dpi);
-                var right = left + (int)(zones[i].Width * dpi);
+                var right = left + (int)(zones[i].Width * Settings.Dpi);
-                var bottom = top + (int)(zones[i].Height * dpi);
+                var bottom = top + (int)(zones[i].Height * Settings.Dpi);
 
                 var index = i * 4;
                 zoneArray[index] = left;
@@ -202,19 +200,8 @@ namespace FancyZonesEditor.Models
                 zoneArray[index+3] = bottom;
             }
 
-            string[] args = Environment.GetCommandLineArgs();
+            var persistZoneSet = Marshal.GetDelegateForFunctionPointer<Native.PersistZoneSet>(pfn);
-            if (args.Length > 1)
+            persistZoneSet(Settings.UniqueKey, Settings.Monitor, _id, zoneCount, zoneArray);
-            {
-                string uniqueId = args[1];
-                uint monitor = 0;
-                if (args.Length > 3)
-                {
-                    monitor = uint.Parse(args[4]);
-                }
-
-                var persistZoneSet = Marshal.GetDelegateForFunctionPointer<Native.PersistZoneSet>(pfn);
-                persistZoneSet(uniqueId, monitor, _id, zoneCount, zoneArray);
-            }
         }
 
         private static readonly string c_registryPath = Settings.RegistryPath + "\\Layouts";

src/modules/fancyzones/editor/FancyZonesEditor/Models/Settings.cs

@@ -23,21 +23,7 @@ namespace FancyZonesEditor
     {
         public Settings()
         {
-            _workArea = System.Windows.SystemParameters.WorkArea;
+            ParseCommandLineArgs();
-            string[] args = Environment.GetCommandLineArgs();
-            if (args.Length > 2)
-            {
-                var foregroundWindow = uint.Parse(args[3]);
-                var screen = System.Windows.Forms.Screen.FromHandle(new IntPtr(foregroundWindow));
-
-                var graphics = System.Drawing.Graphics.FromHwnd(IntPtr.Zero);
-                float dpi = graphics.DpiX / 96;
-                _workArea = new Rect(
-                    screen.WorkingArea.X / dpi,
-                    screen.WorkingArea.Y / dpi,
-                    screen.WorkingArea.Width / dpi,
-                    screen.WorkingArea.Height / dpi);
-            }
 
             // Initialize the five default layout models: Focus, Columns, Rows, Grid, and PriorityGrid
             _defaultModels = new List<LayoutModel>(5);
@@ -62,9 +48,9 @@ namespace FancyZonesEditor
 
             _blankCustomModel = new CanvasLayoutModel("Create new custom", c_blankCustomModelId, (int)_workArea.Width, (int)_workArea.Height);
 
-            _zoneCount = (int)Registry.GetValue(FullRegistryPath, "ZoneCount", 3);
+            _zoneCount = (int)Registry.GetValue(_uniqueRegistryPath, "ZoneCount", 3);
-            _spacing = (int)Registry.GetValue(FullRegistryPath, "Spacing", 16);
+            _spacing = (int)Registry.GetValue(_uniqueRegistryPath, "Spacing", 16);
-            _showSpacing = (int)Registry.GetValue(FullRegistryPath, "ShowSpacing", 1) == 1;
+            _showSpacing = (int)Registry.GetValue(_uniqueRegistryPath, "ShowSpacing", 1) == 1;
 
             UpdateLayoutModels();
         }
@@ -78,7 +64,7 @@ namespace FancyZonesEditor
                 if (_zoneCount != value)
                 {
                     _zoneCount = value;
-                    Registry.SetValue(FullRegistryPath, "ZoneCount", _zoneCount, RegistryValueKind.DWord);
+                    Registry.SetValue(_uniqueRegistryPath, "ZoneCount", _zoneCount, RegistryValueKind.DWord);
                     UpdateLayoutModels();
                     FirePropertyChanged("ZoneCount");
                 }
@@ -95,7 +81,7 @@ namespace FancyZonesEditor
                 if (_spacing != value)
                 {
                     _spacing = value;
-                    Registry.SetValue(FullRegistryPath, "Spacing", _spacing, RegistryValueKind.DWord);
+                    Registry.SetValue(_uniqueRegistryPath, "Spacing", _spacing, RegistryValueKind.DWord);
                     FirePropertyChanged("Spacing");
                 }
             }
@@ -111,7 +97,7 @@ namespace FancyZonesEditor
                 if (_showSpacing != value)
                 {
                     _showSpacing = value;
-                    Registry.SetValue(FullRegistryPath, "ShowSpacing", _showSpacing, RegistryValueKind.DWord);
+                    Registry.SetValue(_uniqueRegistryPath, "ShowSpacing", _showSpacing, RegistryValueKind.DWord);
                     FirePropertyChanged("ShowSpacing");
                 }
             }
@@ -154,6 +140,25 @@ namespace FancyZonesEditor
         }
         private Rect _workArea;
 
+        public static uint Monitor
+        {
+            get { return _monitor; }
+        }
+        private static uint _monitor;
+
+        public static String UniqueKey
+        {
+            get { return _uniqueKey; }
+        }
+        private static String _uniqueKey;
+        private String _uniqueRegistryPath;
+
+        public static float Dpi
+        {
+            get { return _dpi; }
+        }
+        private static float _dpi;
+
         // UpdateLayoutModels
         //  Update the five default layouts based on the new ZoneCount
         private void UpdateLayoutModels()
@@ -251,7 +256,45 @@ namespace FancyZonesEditor
                 _priorityGridModel.ColumnPercents = _gridModel.ColumnPercents;
                 _priorityGridModel.CellChildMap = _gridModel.CellChildMap;
             }
-        }
+        }
+
+        private void ParseCommandLineArgs()
+        {
+            _workArea = System.Windows.SystemParameters.WorkArea;
+            _monitor = 0;
+            _uniqueKey = "";
+            _dpi = 1;
+
+            string[] args = Environment.GetCommandLineArgs();
+            if (args.Length == 5)
+            {
+                // 1 = unique key for per-monitor settings
+                // 2 = layoutid used to generate current layout
+                // 3 = handle to foreground window (used to figure out which monitor to show on)
+                // 4 = handle to monitor (passed back to engine to persist data)
+
+                _uniqueKey = args[1];
+                _uniqueRegistryPath = FullRegistryPath + "\\" + _uniqueKey;
+
+                var foregroundWindow = new IntPtr(uint.Parse(args[3]));
+                var screen = System.Windows.Forms.Screen.FromHandle(foregroundWindow);
+
+                var graphics = System.Drawing.Graphics.FromHwnd(foregroundWindow);
+                _dpi = graphics.DpiX / 96;
+                _workArea = new Rect(
+                    screen.WorkingArea.X / _dpi,
+                    screen.WorkingArea.Y / _dpi,
+                    screen.WorkingArea.Width / _dpi,
+                    screen.WorkingArea.Height / _dpi);
+
+                uint monitor = 0;
+                if (uint.TryParse(args[4], out monitor))
+                {
+                    _monitor = monitor;
+                }
+            }
+        }
+
 
         public IList<LayoutModel> DefaultModels { get { return _defaultModels; } }
         public ObservableCollection<LayoutModel> CustomModels

src/modules/fancyzones/lib/FancyZones.cpp

@@ -237,7 +237,7 @@ void FancyZones::ToggleEditor() noexcept
         m_terminateEditorEvent.reset(CreateEvent(nullptr, true, false, nullptr));
     }
 
-	const HWND foregroundWindow = GetForegroundWindow();
+    const HWND foregroundWindow = GetForegroundWindow();
     if (const HMONITOR monitor = MonitorFromWindow(foregroundWindow, MONITOR_DEFAULTTOPRIMARY))
     {
         std::shared_lock readLock(m_lock);
@@ -245,10 +245,10 @@ void FancyZones::ToggleEditor() noexcept
         if (iter != m_zoneWindowMap.end())
         {
             const std::wstring params =
-				iter->second->UniqueId() + L" " +
+                iter->second->UniqueId() + L" " +
-				std::to_wstring(iter->second->ActiveZoneSet()->LayoutId()) + L" " +
+                std::to_wstring(iter->second->ActiveZoneSet()->LayoutId()) + L" " +
-				std::to_wstring(reinterpret_cast<UINT_PTR>(foregroundWindow)) + L" " +
+                std::to_wstring(reinterpret_cast<UINT_PTR>(foregroundWindow)) + L" " +
-				std::to_wstring(reinterpret_cast<UINT_PTR>(monitor));
+                std::to_wstring(reinterpret_cast<UINT_PTR>(monitor));
 
             SHELLEXECUTEINFO sei{ sizeof(sei) };
             sei.fMask = { SEE_MASK_NOCLOSEPROCESS | SEE_MASK_FLAG_NO_UI };