Add split views within a group

.github/workflows/build.yml

@@ -62,7 +62,7 @@ jobs:
       matrix:
         include:
           - group: architecture
-            suites: 'Architecture,StartupGrouping,WindowIcon'
+            suites: 'Architecture,SplitView,StartupGrouping,WindowIcon'
           - group: operations
             suites: 'GroupOperations,SettingsEditors'
           - group: ui

AGENTS.md

@@ -22,7 +22,9 @@ powershell -NoProfile -ExecutionPolicy Bypass -Command "& ./tests/Run-Tests.ps1
   a later build), so build without exiting first. Starting any copy asks the running one to
   exit as from its tray menu and takes over.
 - New suites must be added to the `$Suites` default in `tests/Run-Tests.ps1`, start
-  with `TestInit.run main`, and reference the app as `#r "Debug/WindowTabs.exe"`.
+  with `TestInit.run main`, and reference the app as `#r "Debug/WindowTabs.exe"`. A suite
+  that moves the real pointer, such as `SplitViewDesktop`, goes in the `ValidateSet` only
+  and runs on request with `-VisibleDesktop` (see [docs/testing.md](docs/testing.md)).
 - Desktop E2E (`tests/Run-DesktopE2E.ps1`) drives real input and takes over the
   desktop; only run it when asked. See [docs/desktop-e2e.md](docs/desktop-e2e.md).
 - CI (`.github/workflows/build.yml`) runs Release checks and three regression
@@ -83,6 +85,8 @@ powershell -NoProfile -ExecutionPolicy Bypass -Command "& ./tests/Run-Tests.ps1
 
 ## Style
 
+- Documents committed to the repository (`docs/`, `README.md`, this file) are written in
+  English; user-visible text in other languages lives only in `Shared/Strings.fs`.
 - Match the surrounding F#: short `///` comments that say why, not what; no banner
   comments; existing helpers (`List2`, `Set2`, `Map2`, `Cell`) where the file uses them.
 - Commit subjects are imperative, sentence case, describe the user-visible effect and

README.md

@@ -58,9 +58,16 @@ right-drag asks, and **Ctrl + Z** in Explorer undoes it.
 - **App rules:** choose which running apps get tabs and which group automatically.
   Under **Groups across apps**, create named groups so windows of different apps join
   one group. Groups made by dragging tabs are remembered and listed there too.
+- **Split view:** show two or more of a group's windows side by side or stacked, as in a
+  browser or editor. Right-click a tab → **Split view** and pick a window for each side, or
+  drag a tab to a window's edge. Drag the bar between the panes to resize them, right-click
+  it to swap, equalize, switch direction or end the split. Shortcuts for a window on the right
+  or below and for moving the focus between panes are under **Settings → Shortcuts**, unset by
+  default.
 - **Workspaces:** save groups and window positions, then restore them onto open windows;
   apps that are not running can be launched and their windows restored.
-- **Taskbar:** optionally combine each group into one taskbar button.
+- **Taskbar:** optionally combine each group into one taskbar button, which shows every
+  app in the group.
 - **Languages:** English, 中文, 日本語.
 
 <a href="docs/images/settings.png"><img src="docs/images/settings.png" width="600" alt="WindowTabs settings" /></a>

Win32/DwmApi.cs

@@ -72,6 +72,8 @@ public sealed class DwmApi
         public static extern int DwmRegisterThumbnail(IntPtr dest, IntPtr src, out IntPtr thumb);
         [DllImport("dwmapi.dll")]
         public static extern int DwmUpdateThumbnailProperties(IntPtr hThumbnail, ref DWM_THUMBNAIL_PROPERTIES props);
+        [DllImport("dwmapi.dll")]
+        public static extern int DwmUnregisterThumbnail(IntPtr hThumbnail);
         [DllImport("dwmapi.dll", EntryPoint = "#113", SetLastError = true)]
         public static extern uint DwmpActivateLivePreview(bool doPeek, IntPtr hWnd, IntPtr hwndTop, bool unknown);
 

Win32/Win32Helper.cs

@@ -161,6 +161,22 @@ private static IntPtr QueryWindowIcon(IntPtr handle, int iconType)
             return icon;
         }
 
+        /// <summary>
+        /// The smallest size the window lets itself be sized to, its invisible borders included;
+        /// an empty size when it does not answer in time.
+        /// </summary>
+        public static Size GetMinTrackSize(IntPtr handle)
+        {
+            var info = new MINMAXINFO();
+            info.ptMaxTrackSize = new SIZE(int.MaxValue, int.MaxValue);
+            IntPtr result;
+            // Foreign windows can be busy or hung. Never block the group on one.
+            if (WinUserApi.SendMessageTimeout(handle, WindowMessages.WM_GETMINMAXINFO, IntPtr.Zero, ref info,
+                SendMessageTimeoutFlags.SMTO_ABORTIFHUNG, 100, out result) == IntPtr.Zero)
+                return Size.Empty;
+            return new Size(Math.Max(0, info.ptMinTrackSize.cx), Math.Max(0, info.ptMinTrackSize.cy));
+        }
+
         public static IntPtr GetWindowIcon(IntPtr handle, int iconType)
         {
             bool small = iconType != IconTypeCodes.ICON_BIG;
@@ -503,6 +519,63 @@ public static void FlashWindow(IntPtr hwnd, uint flags, int count)
             WinUserApi.FlashWindowEx(ref fInfo);
         }
     }
+    /// <summary>
+    /// A per-pixel layered window's picture kept between frames: drawn once per size into a
+    /// memory DC, so each frame only moves the window and sets its opacity. Drawn again at every
+    /// frame of a fade, a window the size of a pane cost a few milliseconds each time.
+    /// </summary>
+    public sealed class LayeredSurface : IDisposable
+    {
+        IntPtr dc;
+        IntPtr bitmap;
+        IntPtr original;
+        Size size;
+
+        public Size Size { get { return size; } }
+
+        public void Render(Bitmap picture)
+        {
+            Release();
+            dc = WinGdiApi.CreateCompatibleDC(IntPtr.Zero);
+            bitmap = picture.GetHbitmap(Color.FromArgb(0));
+            original = WinGdiApi.SelectObject(dc, bitmap);
+            size = picture.Size;
+        }
+
+        public void Update(IntPtr hwnd, Point location, byte alpha)
+        {
+            if (dc == IntPtr.Zero) return;
+            BLENDFUNCTION blend = new BLENDFUNCTION();
+            blend.BlendOp = AlphaChannelFlags.AC_SRC_OVER;
+            blend.BlendFlags = 0;
+            blend.AlphaFormat = AlphaChannelFlags.AC_SRC_ALPHA;
+            blend.SourceConstantAlpha = alpha;
+            POINT srcLocation = new POINT();
+            POINT dstLocation = POINT.FromPoint(location);
+            SIZE dstSize = SIZE.FromSize(size);
+            WinUserApi.UpdateLayeredWindow(hwnd, IntPtr.Zero, ref dstLocation, ref dstSize, dc, ref srcLocation, 0, ref blend, UpdateLayeredWindowFlags.ULW_ALPHA);
+        }
+
+        void Release()
+        {
+            if (dc != IntPtr.Zero)
+            {
+                WinGdiApi.SelectObject(dc, original);
+                WinGdiApi.DeleteObject(bitmap);
+                WinGdiApi.DeleteDC(dc);
+                dc = IntPtr.Zero;
+                bitmap = IntPtr.Zero;
+                original = IntPtr.Zero;
+                size = Size.Empty;
+            }
+        }
+
+        public void Dispose()
+        {
+            Release();
+        }
+    }
+
     public static class ResourceExtractor
     {
         public static void ExtractResourceToFile(string resourceName, string filename)

Win32/WinUser.cs

@@ -2742,6 +2742,8 @@ public static IntPtr GetClassLong(IntPtr hWnd, int nIndex)
         [DllImport("user32.dll", CharSet = CharSet.Auto)]
         public static extern IntPtr SendMessageTimeout(IntPtr hWnd, int message, IntPtr wParam, IntPtr lParam, int flags, int timeout, IntPtr result);
         [DllImport("user32.dll", CharSet = CharSet.Auto)]
+        public static extern IntPtr SendMessageTimeout(IntPtr hWnd, int message, IntPtr wParam, ref MINMAXINFO minMaxInfo, int flags, int timeout, out IntPtr result);
+        [DllImport("user32.dll", CharSet = CharSet.Auto)]
         public static extern IntPtr SendMessageTimeout(IntPtr hWnd, int message, int wParam, StringBuilder buffer, int flags, int timeout, out IntPtr result);
         [DllImport("user32.dll", CharSet = CharSet.Auto)]
 		public static extern IntPtr SendMessage(IntPtr hWnd, int message, IntPtr wParam, StringBuilder lParam);