Back-port DarkMode Fixes to Preview 6.

.github/copilot-instructions.md

@@ -423,6 +423,16 @@ using Pen focusPen = new(focusColor) // Use 'using' with type name and omit type
 
 - **Don't XML-comment local functions**, as this is not supported. Instead, be more verbose in a comment if the local function's purpose is not immediately obvious.
 
+- **Use `<inheritdoc/>` for inherited members** to avoid duplication and ensure consistency in documentation.
+  ```csharp
+  /// <inheritdoc/>
+  public override void OnClick(EventArgs e)
+  {
+      base.OnClick(e);
+      // Additional logic here
+  }
+  ```
+
 ### 1.9 File Structure and Formatting
 
 - **Use file-scoped namespaces**

.github/copilot/GDI/DarkModeButtonRendererCodeGenerationInstructions.md

@@ -0,0 +1,88 @@
+Create a ButtonDarkModeRenderer class similar to the existing ButtonRenderer in System.Windows.Forms, but specifically designed for dark mode rendering. The class should follow the same architectural patterns as the provided ButtonRenderer while implementing Windows 11 dark mode visual styling.
+
+## Visual Styling Details
+
+### Button Shapes and Corners
+1. All buttons should have rounded corners with a radius of approximately 4-5 pixels
+2. The corners must be properly anti-aliased
+3. For the rounded corners, implement transparency at the very edges so the parent background shows through correctly - this is crucial as the button's rectangular client area includes the corners, but visually they should appear rounded
+4. Use alpha blending at the rounded edges to create a smooth transition between the button and its background
+
+### Color Schemes
+1. Normal Button (non-default):
+   - Background: Dark gray (#2B2B2B) when not hovered
+   - Hover state: Slightly lighter gray (#3B3B3B) - this change should be clearly noticeable
+   - Pressed state: Even lighter gray (#4B4B4B) with a subtle inward appearance
+   - Disabled state: Very dark gray (#252525) with reduced opacity text (around 40% opacity)
+
+2. Default Button:
+   - Background: Accent color (purple tone similar to #6B2FBF when not hovered)
+   - Hover state: Slightly lighter accent color (#7C3FD0)
+   - Pressed state: Darker accent color (#5B1FAF) with subtle inward appearance
+   - Disabled state: Desaturated accent color with reduced opacity text
+
+3. Text Colors:
+   - Normal state: Light gray (#E0E0E0) for standard buttons, white (#FFFFFF) for default buttons
+   - Disabled state: Reduced opacity version of normal text color (around 40% opacity)
+
+### Border Styles
+1. None border style:
+   - No visible border, matching Windows 11 dark mode
+   - Only the fill color and rounded corners are visible
+
+2. Single border style:
+   - Hair-thin (1px) border with a color that provides sufficient contrast
+   - For normal buttons: Medium gray (#555555)
+   - For default buttons: Slightly darker version of the accent color
+
+3. 3D border style:
+   - Slightly thicker border (1-2px)
+   - For normal buttons: Top/left slightly lighter (#555555), bottom/right slightly darker (#222222)
+   - For default buttons: Similar effect but with accent color variations
+   - On hover: Subtly enhance the contrast between the edges
+   - On press: Invert the light/dark edges to create an inset appearance
+
+### Focus Indication
+1. When a button has focus, draw a 1px dotted outline 2px inside the button's edge
+2. The focus indicator should follow the rounded corners
+3. For normal buttons: Use a light gray (#AAAAAA) for the focus indicator
+4. For default buttons: Use white (#FFFFFF) or very light purple for the focus indicator
+5. Ensure the focus indicator doesn't interfere with text or image rendering
+
+### State Transitions
+1. All state changes (hover, press, etc.) should have a subtle fade/transition effect if possible
+2. The hover and pressed state visual changes should be more pronounced than in the standard renderer
+3. Implement a slight scale-down effect (approximately 0.5-1% reduction) when buttons are pressed
+
+## Functional Requirements
+
+1. Maintain complete feature parity with ButtonRenderer:
+   - Support for text rendering with all the same formatting options
+   - Support for image rendering with the same positioning options
+   - Support for combined text and image rendering
+   - Proper handling of all PushButtonState values
+
+2. Use SystemColors appropriately:
+   - Rely on the dark mode SystemColors when Application.IsDarkModeEnabled is true
+   - If specific colors need adjustments beyond SystemColors, implement these within the renderer
+
+3. Transparency and background handling:
+   - Properly support the IsBackgroundPartiallyTransparent method
+   - Correctly implement the DrawParentBackground method to handle transparent areas
+   - Ensure transparent corners are properly rendered showing the parent background
+
+4. Implement all public methods present in ButtonRenderer with identical signatures and parameters
+
+5. Thread safety:
+   - Maintain the same thread-safety approach as ButtonRenderer with ThreadStatic renderer instances
+
+## Implementation Notes
+
+1. Follow the same pattern as ButtonRenderer, creating a static class with identical method signatures
+2. Do not add any additional features beyond what is specified
+3. Maintain backward compatibility with existing button rendering behavior
+4. Handle fallback for systems where visual styles are not enabled or supported
+5. Provide appropriate XML documentation following the same style as the original ButtonRenderer
+6. Prioritize rendering performance, especially for the alpha-blended rounded corners
+
+The class should integrate seamlessly with the existing WinForms infrastructure while providing modern Windows 11 dark mode visuals.

Winforms.sln

@@ -213,9 +213,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Copilot", "Copilot", "{02EA
 		.github\copilot-instructions.md = .github\copilot-instructions.md
 	EndProjectSection
 EndProject
-Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Rendering", "Rendering", "{D619FF8C-D99A-48AB-B16B-2F0E819B46D5}"
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "GDI", "GDI", "{D619FF8C-D99A-48AB-B16B-2F0E819B46D5}"
 	ProjectSection(SolutionItems) = preProject
-		.github\copilot\GDIPlus-copilot-instructions.md = .github\copilot\GDIPlus-copilot-instructions.md
+		.github\copilot\GDI\DarkModeButtonRendererCodeGenerationInstructions.md = .github\copilot\GDI\DarkModeButtonRendererCodeGenerationInstructions.md
+		.github\copilot\GDI\GDIPlus-copilot-instructions.md = .github\copilot\GDI\GDIPlus-copilot-instructions.md
 	EndProjectSection
 EndProject
 Global

src/System.Windows.Forms/System/Windows/Forms/Control.cs

@@ -162,6 +162,8 @@ public unsafe partial class Control :
     internal const string ExplorerThemeIdentifier = "Explorer";
     internal const string ItemsViewThemeIdentifier = "ItemsView";
     internal const string ComboBoxButtonThemeIdentifier = "CFD";
+    internal const string BannerContainerThemeIdentifier = "FileExplorerBannerContainer";
+    internal const string ComboboxClassIdentifier = "COMBOBOX";
 
     private const short PaintLayerBackground = 1;
     private const short PaintLayerForeground = 2;
@@ -9207,9 +9209,12 @@ internal virtual void RecreateHandleCore()
 
             bool focused = ContainsFocus;
 
-            Debug.WriteLineIf(CoreSwitches.PerfTrack.Enabled, $"RecreateHandle: {GetType().FullName} [Text={Text}]");
+            Debug.WriteLineIf(
+                CoreSwitches.PerfTrack.Enabled,
+                $"RecreateHandle: {GetType().FullName} [Text={Text}]");
 
             bool created = GetState(States.Created);
+
             if (GetState(States.TrackingMouseEvent))
             {
                 SetState(States.MouseEnterPending, true);
@@ -9232,9 +9237,11 @@ internal virtual void RecreateHandleCore()
                 if (ChildControls is { } children && children.Count > 0)
                 {
                     controlSnapshot = new Control[children.Count];
+
                     for (int i = 0; i < children.Count; i++)
                     {
                         Control childControl = children[i];
+
                         if (childControl is not null && childControl.IsHandleCreated)
                         {
                             // SetParent to parking window
@@ -9294,6 +9301,7 @@ internal virtual void RecreateHandleCore()
                     for (int i = 0; i < controlSnapshot.Length; i++)
                     {
                         Control? childControl = controlSnapshot[i];
+
                         if (childControl is not null && childControl.IsHandleCreated)
                         {
                             // Re-parent the control.

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/Button.cs

@@ -75,11 +75,11 @@ public AutoSizeMode AutoSizeMode
 
     protected override AccessibleObject CreateAccessibilityInstance() => new ButtonAccessibleObject(this);
 
-    internal override ButtonBaseAdapter CreateFlatAdapter() => new ButtonFlatAdapter(this);
+    internal override ButtonBaseAdapter CreateFlatAdapter() => DarkModeAdapterFactory.CreateFlatAdapter(this);
 
-    internal override ButtonBaseAdapter CreatePopupAdapter() => new ButtonPopupAdapter(this);
+    internal override ButtonBaseAdapter CreatePopupAdapter() => DarkModeAdapterFactory.CreatePopupAdapter(this);
 
-    internal override ButtonBaseAdapter CreateStandardAdapter() => new ButtonStandardAdapter(this);
+    internal override ButtonBaseAdapter CreateStandardAdapter() => DarkModeAdapterFactory.CreateStandardAdapter(this);
 
     internal override Size GetPreferredSizeCore(Size proposedConstraints)
     {
@@ -121,6 +121,7 @@ protected override CreateParams CreateParams
             else
             {
                 cp.Style |= PInvoke.BS_PUSHBUTTON;
+
                 if (IsDefault)
                 {
                     cp.Style |= PInvoke.BS_DEFPUSHBUTTON;

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonBase.cs

@@ -337,6 +337,44 @@ protected internal bool IsDefault
     /// <summary>
     ///  Gets or sets the flat style appearance of the button control.
     /// </summary>
+    /// <remarks>
+    ///  <para>
+    ///   The <see cref="FlatStyle"/> property determines how the button is rendered. The following values are supported:
+    ///  </para>
+    ///  <list type="bullet">
+    ///   <item>
+    ///    <term><see cref="FlatStyle.Standard"/></term>
+    ///    <description>
+    ///     The default style. The button is not wrapping the system button. It is rendered using the StandardButton adapter.
+    ///     VisualStyleRenderer from the OS is used for certain parts, which may have issues in high-resolution scenarios.
+    ///     Dark mode works to some extent, but improvements are needed.
+    ///    </description>
+    ///   </item>
+    ///   <item>
+    ///    <term><see cref="FlatStyle.Popup"/></term>
+    ///    <description>
+    ///     The button is fully owner-drawn. No rendering is delegated to the OS, not even VisualStyleRenderer.
+    ///     This style works well in dark mode and is fully controlled by the application.
+    ///     3D effects are expected but may not be rendered; consider revisiting for meaningful styling.
+    ///    </description>
+    ///   </item>
+    ///   <item>
+    ///    <term><see cref="FlatStyle.Flat"/></term>
+    ///    <description>
+    ///     The button is fully owner-drawn, with no OS calls or VisualStyleRenderer usage.
+    ///     This fits modern design language and works well in dark mode.
+    ///    </description>
+    ///   </item>
+    ///   <item>
+    ///    <term><see cref="FlatStyle.System"/></term>
+    ///    <description>
+    ///     The button wraps the system button and is not owner-drawn.
+    ///     No <c>OnPaint</c>, <c>OnPaintBackground</c>, or adapter is involved.
+    ///     In dark mode, this style is used as a fallback for Standard-style buttons.
+    ///    </description>
+    ///   </item>
+    ///  </list>
+    /// </remarks>
     [SRCategory(nameof(SR.CatAppearance))]
     [DefaultValue(FlatStyle.Standard)]
     [Localizable(true)]
@@ -356,6 +394,7 @@ public FlatStyle FlatStyle
             _flatStyle = value;
             LayoutTransaction.DoLayoutIf(AutoSize, ParentInternal, this, PropertyNames.FlatStyle);
             Invalidate();
+
             UpdateOwnerDraw();
         }
     }
@@ -409,12 +448,18 @@ public Image? Image
             StopAnimate();
 
             _image = value;
+
             if (_image is not null)
             {
                 ImageIndex = ImageList.Indexer.DefaultIndex;
                 ImageList = null;
             }
 
+            // If we have an Image, for some flat styles we need to change the rendering approach from
+            // being a wrapper around the Win32 control to being owner-drawn. The Win32 control does not
+            // support images in the same flexible way as we need it.
+            UpdateOwnerDraw();
+
             LayoutTransaction.DoLayoutIf(AutoSize, ParentInternal, this, PropertyNames.Image);
             Animate();
             Invalidate();
@@ -620,7 +665,14 @@ internal virtual Rectangle OverChangeRectangle
         }
     }
 
-    private protected virtual bool OwnerDraw => FlatStyle != FlatStyle.System;
+    /// <summary>
+    ///  OwnerDraw ultimately determines, if we're wrapping the respective Win32 control
+    ///  (Button, CheckBox, RadioButton - OwnerDraw == false) or not. When we're not OwnerDraw,
+    ///  both Light- and DarkMode are (and can be) rendered by the System, but then there is
+    ///  no image rendering, and no OnPaint. This is the original behavior of the Win32 controls.
+    /// </summary>
+    private protected virtual bool OwnerDraw =>
+            FlatStyle != FlatStyle.System;
 
     bool? ICommandBindingTargetProvider.PreviousEnabledStatus { get; set; }
 
@@ -960,15 +1012,20 @@ public override Size GetPreferredSize(Size proposedSize)
 
     internal override Size GetPreferredSizeCore(Size proposedConstraints)
     {
-        Size preferedSize = Adapter.GetPreferredSizeCore(proposedConstraints);
-        return LayoutUtils.UnionSizes(preferedSize + Padding.Size, MinimumSize);
+        Size preferredSize = Adapter.GetPreferredSizeCore(proposedConstraints);
+        return LayoutUtils.UnionSizes(preferredSize + Padding.Size, MinimumSize);
     }
 
+    /// <summary>
+    ///  Returns an adapter for Rendering one of the FlatStyles. Note, that we always render
+    ///  buttons ourselves, except when the User explicitly requests FlatStyle.System rendering!
+    /// </summary>
     internal ButtonBaseAdapter Adapter
     {
         get
         {
-            if (_adapter is null || FlatStyle != _cachedAdapterType)
+            if (_adapter is null
+                || FlatStyle != _cachedAdapterType)
             {
                 switch (FlatStyle)
                 {
@@ -980,7 +1037,6 @@ internal ButtonBaseAdapter Adapter
                         break;
                     case FlatStyle.Flat:
                         _adapter = CreateFlatAdapter();
-                        ;
                         break;
                     default:
                         Debug.Fail($"Unsupported FlatStyle: \"{FlatStyle}\"");
@@ -1238,7 +1294,11 @@ private void SetFlag(int flag, bool value)
 
     private bool ShouldSerializeImage() => _image is not null;
 
-    private void UpdateOwnerDraw()
+    // Indicates whether this control uses owner drawing, enabling UserPaint and determining
+    // if we wrap the native Win32 control (OwnerDraw == false) or render it ourselves.
+    // Also needed to detect a Dark Mode opt-out for FlatStyle.Standard when system painting
+    // cannot be forced.
+    private protected void UpdateOwnerDraw()
     {
         if (OwnerDraw != GetStyle(ControlStyles.UserPaint))
         {

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/ButtonBaseAdapter.cs

@@ -23,11 +23,12 @@ internal abstract partial class ButtonBaseAdapter
     /// <summary>
     ///  Returns a darkened color according to the required color contrast ratio.
     /// </summary>
-    private protected static Color GetContrastingBorderColor(Color buttonBorderShadowColor) => Color.FromArgb(
-        buttonBorderShadowColor.A,
-        (int)(buttonBorderShadowColor.R * 0.8f),
-        (int)(buttonBorderShadowColor.G * 0.8f),
-        (int)(buttonBorderShadowColor.B * 0.8f));
+    private protected static Color GetContrastingBorderColor(Color buttonBorderShadowColor) =>
+        Color.FromArgb(
+            buttonBorderShadowColor.A,
+            (int)(buttonBorderShadowColor.R * 0.8f),
+            (int)(buttonBorderShadowColor.G * 0.8f),
+            (int)(buttonBorderShadowColor.B * 0.8f));
 
     internal void Paint(PaintEventArgs e)
     {
@@ -48,6 +49,7 @@ internal void Paint(PaintEventArgs e)
     internal virtual Size GetPreferredSizeCore(Size proposedSize)
     {
         LayoutOptions? options = default;
+
         using (var screen = GdiCache.GetScreenHdc())
         using (PaintEventArgs e = new(screen, default))
         {
@@ -277,11 +279,10 @@ private void Draw3DBorderRaised(IDeviceContext deviceContext, ref Rectangle boun
         hdc.DrawLine(topLeftInsetPen, p2, p3);      // Left (up-down)
 
         // Bottom + right inset
-
         using CreatePenScope bottomRightInsetPen = new(
             disabledHighContrast
-            ? colors.WindowDisabled
-            : stockColor ? SystemColors.ControlDark : colors.ButtonShadow);
+                ? colors.WindowDisabled
+                : stockColor ? SystemColors.ControlDark : colors.ButtonShadow);
 
         p1.Offset(0, -1);                           // Need to paint last pixel too.
         hdc.DrawLine(bottomRightInsetPen, p3, p4);  // Bottom (left-right)
@@ -342,6 +343,7 @@ internal static void DrawFlatBorderWithSize(
             g.FillRectangle(brush, right);
             g.FillRectangle(brush, top);
             g.FillRectangle(brush, bottom);
+
             return;
         }
 
@@ -648,10 +650,12 @@ private ColorOptions CommonRender(IDeviceContext deviceContext) =>
     internal static ColorOptions PaintFlatRender(Graphics g, Color foreColor, Color backColor, bool enabled) =>
         CommonRender(g, foreColor, backColor, enabled);
 
-    protected ColorOptions PaintFlatRender(IDeviceContext deviceContext) => CommonRender(deviceContext);
+    protected ColorOptions PaintFlatRender(IDeviceContext deviceContext)
+        => CommonRender(deviceContext);
 
     internal static ColorOptions PaintPopupRender(Graphics g, Color foreColor, Color backColor, bool enabled) =>
         CommonRender(g, foreColor, backColor, enabled);
 
-    protected ColorOptions PaintPopupRender(IDeviceContext deviceContext) => CommonRender(deviceContext);
+    protected ColorOptions PaintPopupRender(IDeviceContext deviceContext)
+        => CommonRender(deviceContext);
 }