Some NC paint research

Also add guidelines to editor.config.

.editorconfig

@@ -1,6 +1,9 @@
 # Remove the line below if you want to inherit .editorconfig settings from higher directories
 root = true
 
+[*]
+guidelines = 120 1px dotted 504CFF00, 150 1px dotted 50FF6A00
+
 # Test .cs files
 [**/*Tests.cs]
 

src/samples/Petzold/5th/Clover/Program.cs

@@ -44,9 +44,9 @@ protected override LRESULT WindowProcedure(HWND window, MessageType message, WPA
                     using HRGN region1 = HRGN.FromEllipse(_cxClient / 2, _cyClient / 3, _cxClient, 2 * _cyClient / 3);
                     using HRGN region2 = HRGN.FromEllipse(_cxClient / 3, 0, 2 * _cxClient / 3, _cyClient / 2);
                     using HRGN region3 = HRGN.FromEllipse(_cxClient / 3, _cyClient / 2, 2 * _cxClient / 3, _cyClient);
-                    using HRGN region4 = HRGN.CombineRegion(region0, region1, RegionCombineMode.Or);
-                    using HRGN region5 = HRGN.CombineRegion(region2, region3, RegionCombineMode.Or);
-                    _hrgnClip = HRGN.CombineRegion(region4, region5, RegionCombineMode.Xor);
+                    using HRGN region4 = region0.Combine(region1, RegionCombineMode.Or);
+                    using HRGN region5 = region2.Combine(region3, RegionCombineMode.Or);
+                    _hrgnClip = region4.Combine(region5, RegionCombineMode.Xor);
 
                     return (LRESULT)0;
                 }

src/thirtytwo/Messages/Message.NonClientPaint.cs

@@ -0,0 +1,50 @@
+// Copyright (c) Jeremy W. Kuhne. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Windows;
+
+public static partial class Message
+{
+    /// <summary>
+    ///  Wrapper for the <see href="https://learn.microsoft.com/windows/win32/gdi/wm-ncpaint">frame painting message</see>.
+    /// </summary>
+    public readonly unsafe ref struct NonClientPaint(WPARAM wParam)
+    {
+        /// <summary>
+        ///  Update region clipped to the window frame.
+        /// </summary>
+        /// <remarks>
+        ///  <para>
+        ///   This may sometimes be <see cref="HRGN.Full"/> to indicate the entire window.
+        ///  </para>
+        ///  <para>
+        ///   This is effectively <see cref="Interop.GetWindowRect(HWND, RECT*)"/>. If the window has a clipping region
+        ///   set via <see cref="Interop.SetWindowRgn(HWND, HRGN, BOOL)"/>, that will be intersected with the rect.
+        ///   This isn't very likely as having a clipping region
+        ///   <see href="https://learn.microsoft.com/windows/win32/controls/cookbook-overview#when-visual-styles-are-not-applied">
+        ///   prevents theming</see>.
+        ///  </para>
+        /// </remarks>
+        public HRGN UpdateRegion => (HRGN)(nint)wParam;
+
+        public HDC GetDC(HWND window, bool copyRegion = true)
+        {
+            // GetDCEx will take ownership of the region.
+            HRGN updateRegion = UpdateRegion;
+            if (updateRegion.IsFull)
+            {
+                updateRegion = HRGN.Null;
+            }
+
+            HRGN region = copyRegion && !updateRegion.IsNull ? updateRegion.Copy() : updateRegion;
+
+            // GetDC (as opposed to GetDCEx) will call GetDCEx with a special flag that will set flags based
+            // on the window's style. WS_CLIPCHILDREN will set DCX_CLIPCHILDREN for example.
+
+            return Interop.GetDCEx(
+                window,
+                region,
+                region.IsNull ? GET_DCX_FLAGS.DCX_WINDOW : GET_DCX_FLAGS.DCX_WINDOW | GET_DCX_FLAGS.DCX_INTERSECTRGN);
+        }
+    }
+}

src/thirtytwo/NativeMethods.txt

@@ -144,6 +144,7 @@ GetCurrentThreadId
 GetCursorPos
 GetDC
 GetDCBrushColor
+GetDCEx
 GetDeviceCaps
 GetDialogBaseUnits
 GetDialogBaseUnits

src/thirtytwo/Win32/Graphics/Gdi/HRGN.cs

@@ -10,6 +10,11 @@ public unsafe partial struct HRGN : IDisposable
 {
     public void Dispose()
     {
+        if (IsFull)
+        {
+            return;
+        }
+
         if (!IsNull)
         {
             Interop.DeleteObject(this);
@@ -18,6 +23,18 @@ public void Dispose()
         Unsafe.AsRef(in this) = default;
     }
 
+    /// <summary>
+    ///  Special <see cref="HRGN"/> sent during WM_NCPAINT to indicate the entire window.
+    /// </summary>
+    public static HRGN Full { get; } = (HRGN)1;
+
+    /// <summary>
+    ///  Is special <see cref="HRGN.Full"/> value.
+    /// </summary>
+    public bool IsFull => Value == Full.Value;
+
+    // There is also a special HRGN_MONITOR (2) that is used when maximized. Not sure if this escapes.
+
     public static HRGN FromRectangle(Rectangle rectangle) =>
         Interop.CreateRectRgn(rectangle.X, rectangle.Y, rectangle.Right, rectangle.Bottom);
 
@@ -30,13 +47,27 @@ public static HRGN FromEllipse(Rectangle bounds) =>
 
     public static HRGN CreateEmpty() => Interop.CreateRectRgn(0, 0, 0, 0);
 
-    public static HRGN CombineRegion(HRGN first, HRGN second, RegionCombineMode combineMode) =>
-        CombineRegion(first, second, combineMode, out _);
+    public HRGN Combine(HRGN region, RegionCombineMode combineMode) =>
+        Combine(region, combineMode, out _);
+
+    public HRGN Combine(HRGN region, RegionCombineMode combineMode, out RegionType type)
+    {
+        HRGN hrgn = CreateEmpty();
+        type = (RegionType)Interop.CombineRgn(hrgn, this, region, (RGN_COMBINE_MODE)combineMode);
+        if (type == RegionType.Error)
+        {
+            hrgn.Dispose();
+        }
+
+        return hrgn;
+    }
+
+    public HRGN Copy() => Copy(out _);
 
-    public static HRGN CombineRegion(HRGN first, HRGN second, RegionCombineMode combineMode, out RegionType type)
+    public HRGN Copy(out RegionType type)
     {
         HRGN hrgn = CreateEmpty();
-        type = (RegionType)Interop.CombineRgn(hrgn, first, second, (RGN_COMBINE_MODE)combineMode);
+        type = (RegionType)Interop.CombineRgn(hrgn, this, default, (RGN_COMBINE_MODE)RegionCombineMode.Copy);
         if (type == RegionType.Error)
         {
             hrgn.Dispose();