Update the OwnerDraw flag when BackgroundImage changes

src/System.Windows.Forms/PublicAPI.Unshipped.txt

@@ -1,3 +1,4 @@
+override System.Windows.Forms.Button.BackgroundImage.set -> void
 override System.Windows.Forms.ButtonBase.OnBackColorChanged(System.EventArgs! e) -> void
 override System.Windows.Forms.ButtonBase.OnForeColorChanged(System.EventArgs! e) -> void
 static System.Windows.Forms.Application.SetColorMode(System.Windows.Forms.SystemColorMode systemColorMode) -> void

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

@@ -148,6 +148,21 @@ public virtual DialogResult DialogResult
         }
     }
 
+    public override Image? BackgroundImage
+    {
+        set
+        {
+            base.BackgroundImage = value;
+
+            if (Application.IsDarkModeEnabled)
+            {
+                // BackgroundImage changes may affect rendering logic,
+                // so we manually update the OwnerDraw flag to ensure correct visual behavior.
+                UpdateOwnerDraw();
+            }
+        }
+    }
+
     /// <summary>
     ///  Defines, whether the control is owner-drawn. Based on this,
     ///  the UserPaint flags get set, which in turn makes it later
@@ -161,7 +176,6 @@ private protected override bool OwnerDraw
         get
         {
             if (Application.IsDarkModeEnabled
-
                 // The SystemRenderer cannot render images. So, we flip to our
                 // own DarkMode renderer, if we need to render images, except if...
                 && Image is null

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

@@ -547,21 +547,6 @@ internal void PaintField(
     /// </summary>
     internal void PaintImage(PaintEventArgs e, LayoutData layout)
     {
-        if (Application.IsDarkModeEnabled && Control.DarkModeRequestState is true && Control.BackgroundImage is not null)
-        {
-            Rectangle bounds = Control.ClientRectangle;
-            bounds.Inflate(-ButtonBorderSize, -ButtonBorderSize);
-            ControlPaint.DrawBackgroundImage(
-                e.GraphicsInternal,
-                Control.BackgroundImage,
-                Color.Transparent,
-                Control.BackgroundImageLayout,
-                Control.ClientRectangle,
-                bounds,
-                Control.DisplayRectangle.Location,
-                Control.RightToLeft);
-        }
-
         if (Control.Image is not null)
         {
             // Setup new clip region & draw

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/DarkMode/ButtonDarkModeAdapter.cs

@@ -70,6 +70,32 @@ private Color GetButtonBackColor(PushButtonState state)
         return textColor;
     }
 
+    internal void PaintBackgroundImage(PaintEventArgs e, int borderSize, Rectangle paddedBounds)
+    {
+        if (Application.IsDarkModeEnabled && Control.DarkModeRequestState is true && Control.BackgroundImage is not null)
+        {
+            Rectangle bounds = paddedBounds;
+            if (Control.FlatStyle == FlatStyle.Popup)
+            {
+                bounds.Inflate(-1, -1);
+            }
+            else
+            {
+                bounds.Inflate(-1 - borderSize, -1 - borderSize);
+            }
+
+            ControlPaint.DrawBackgroundImage(
+                e.GraphicsInternal,
+                Control.BackgroundImage,
+                Color.Transparent,
+                Control.BackgroundImageLayout,
+                paddedBounds,
+                bounds,
+                bounds.Location,
+                Control.RightToLeft);
+        }
+    }
+
     internal override void PaintUp(PaintEventArgs e, CheckState state)
     {
         try
@@ -86,13 +112,18 @@ internal override void PaintUp(PaintEventArgs e, CheckState state)
                 g,
                 Control.ClientRectangle,
                 Control.FlatStyle,
+                Control.FlatAppearance.BorderSize,
                 pushButtonState,
                 Control.IsDefault,
                 Control.Focused,
                 Control.ShowFocusCues,
                 Control.Parent?.BackColor ?? Control.BackColor,
                 GetButtonBackColor(pushButtonState),
                 _ => PaintImage(e, layout),
+                _ => PaintBackgroundImage(
+                    e,
+                    Control.FlatAppearance.BorderSize,
+                    Control.ClientRectangle),
                 () => PaintField(
                     e,
                     layout,
@@ -124,13 +155,18 @@ internal override void PaintDown(PaintEventArgs e, CheckState state)
                 g,
                 Control.ClientRectangle,
                 Control.FlatStyle,
+                Control.FlatAppearance.BorderSize,
                 PushButtonState.Pressed,
                 Control.IsDefault,
                 Control.Focused,
                 Control.ShowFocusCues,
                 Control.Parent?.BackColor ?? Control.BackColor,
                 GetButtonBackColor(PushButtonState.Pressed),
                 _ => PaintImage(e, layout),
+                _ => PaintBackgroundImage(
+                    e,
+                    Control.FlatAppearance.BorderSize,
+                    Control.ClientRectangle),
                 () => PaintField(
                     e,
                     layout,
@@ -156,19 +192,23 @@ internal override void PaintOver(PaintEventArgs e, CheckState state)
             var g = e.GraphicsInternal;
             var smoothingMode = g.SmoothingMode;
             g.SmoothingMode = Drawing.Drawing2D.SmoothingMode.AntiAlias;
-
             LayoutData layout = CommonLayout().Layout();
             ButtonDarkModeRenderer.RenderButton(
                 g,
                 Control.ClientRectangle,
                 Control.FlatStyle,
+                Control.FlatAppearance.BorderSize,
                 PushButtonState.Hot,
                 Control.IsDefault,
                 Control.Focused,
                 Control.ShowFocusCues,
                 Control.Parent?.BackColor ?? Control.BackColor,
                 GetButtonBackColor(PushButtonState.Hot),
                 _ => PaintImage(e, layout),
+                _ => PaintBackgroundImage(
+                    e,
+                    Control.FlatAppearance.BorderSize,
+                    Control.ClientRectangle),
                 () => PaintField(
                     e,
                     layout,

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/DarkMode/ButtonDarkModeRendererBase.cs

@@ -32,13 +32,15 @@ public void RenderButton(
         Graphics graphics,
         Rectangle bounds,
         FlatStyle flatStyle,
+        int borderSize,
         PushButtonState state,
         bool isDefault,
         bool focused,
         bool showFocusCues,
         Color parentBackgroundColor,
         Color backColor,
         Action<Rectangle> paintImage,
+        Action<Rectangle> paintBackgroundImage,
         Action paintField)
     {
         ArgumentNullException.ThrowIfNull(graphics);
@@ -61,11 +63,15 @@ public void RenderButton(
                 height: bounds.Height - padding.Vertical);
 
             // Draw button background and get content bounds
-            Rectangle contentBounds = DrawButtonBackground(graphics, paddedBounds, state, isDefault, backColor);
+            Rectangle contentBounds = DrawButtonBackground(graphics, paddedBounds, borderSize, state, isDefault, backColor);
+
+            paintBackgroundImage(paddedBounds);
 
             // Paint image and field using the provided delegates
             paintImage(contentBounds);
 
+            DrawButtonBorder(graphics, bounds, borderSize, state, isDefault);
+
             paintField();
 
             if (focused && showFocusCues)
@@ -76,7 +82,9 @@ public void RenderButton(
         }
     }
 
-    public abstract Rectangle DrawButtonBackground(Graphics graphics, Rectangle bounds, PushButtonState state, bool isDefault, Color backColor);
+    public abstract void DrawButtonBorder(Graphics graphics, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault);
+
+    public abstract Rectangle DrawButtonBackground(Graphics graphics, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault, Color backColor);
 
     public abstract void DrawFocusIndicator(Graphics graphics, Rectangle contentBounds, bool isDefault);
 

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/DarkMode/FlatButtonDarkModeRenderer.cs

@@ -17,21 +17,19 @@ namespace System.Windows.Forms;
 internal sealed class FlatButtonDarkModeRenderer : ButtonDarkModeRendererBase
 {
     private const int FocusIndicatorInflate = -3;
-    private const int CornerRadius = 6;
-    private static readonly Size s_corner = new(CornerRadius, CornerRadius);
 
     private protected override Padding PaddingCore { get; } = new(0);
 
     public override Rectangle DrawButtonBackground(
-        Graphics graphics, Rectangle bounds, PushButtonState state, bool isDefault, Color backColor)
+        Graphics graphics, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault, Color backColor)
     {
         // fill background
         using var back = backColor.GetCachedSolidBrushScope();
-        graphics.FillRectangle(back, bounds);
 
-        // draw border identical to Win32
-        DrawButtonBorder(graphics, bounds, state, isDefault);
+        Rectangle rectangle = bounds;
+        rectangle.Inflate(-1 - borderSize, -1 - borderSize);
 
+        graphics.FillRectangle(back, rectangle);
         // return inner content area (border + 1 px system padding)
         return Rectangle.Inflate(bounds, -3, -3);
     }
@@ -77,33 +75,29 @@ public override Color GetBackgroundColor(PushButtonState state, bool isDefault)
                 _ => DefaultColors.StandardBackColor
             };
 
-    private static void DrawButtonBorder(Graphics g, Rectangle bounds, PushButtonState state, bool isDefault)
+    public override void DrawButtonBorder(Graphics g, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault)
     {
         g.SmoothingMode = SmoothingMode.AntiAlias;
 
         // Win32 draws its stroke fully *inside* the control → inset by 1 px
         Rectangle outer = Rectangle.Inflate(bounds, -1, -1);
 
-        DrawSingleBorder(g, outer, GetBorderColor(state));
+        DrawSingleBorder(g, outer, borderSize, GetBorderColor(state));
 
         // Default button gets a second 1‑px border one pixel further inside
         if (isDefault)
         {
             Rectangle inner = Rectangle.Inflate(outer, -1, -1);
-            DrawSingleBorder(g, inner, DefaultColors.AcceptFocusIndicatorBackColor);
+            DrawSingleBorder(g, inner, borderSize, DefaultColors.AcceptFocusIndicatorBackColor);
         }
     }
 
-    private static void DrawSingleBorder(Graphics g, Rectangle rect, Color color)
+    private static void DrawSingleBorder(Graphics g, Rectangle rect, int borderSize, Color color)
     {
         g.SmoothingMode = SmoothingMode.AntiAlias;
 
-        using var path = new GraphicsPath();
-        path.AddRoundedRectangle(rect, s_corner);
-
-        // a 1‑px stroke, aligned *inside*, is exactly what Win32 draws
-        using var pen = new Pen(color) { Alignment = PenAlignment.Inset };
-        g.DrawPath(pen, path);
+        using var pen = new Pen(color, borderSize) { Alignment = PenAlignment.Inset };
+        g.DrawRectangle(pen, rect);
     }
 
     private static Color GetBorderColor(PushButtonState state) =>

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/DarkMode/IButtonRenderer.cs

@@ -43,24 +43,27 @@ void RenderButton(
         Graphics graphics,
         Rectangle bounds,
         FlatStyle flatStyle,
+        int BorderSize,
         PushButtonState state,
         bool isDefault,
         bool focused,
         bool showFocusCues,
         Color parentBackgroundColor,
         Color backColor,
         Action<Rectangle> paintImage,
+        Action<Rectangle> paintBackgroundImage,
         Action paintField);
 
     /// <summary>
     ///  Draws button background with appropriate styling.
     /// </summary>
     /// <param name="graphics">Graphics context to draw on</param>
     /// <param name="bounds">Bounds of the button</param>
+    /// <param name="borderSize">BorderSize of the button</param>
     /// <param name="state">State of the button (normal, hot, pressed, disabled)</param>
     /// <param name="isDefault">True if button is the default button</param>
     /// <returns>The content bounds (area inside the button for text/image)</returns>
-    Rectangle DrawButtonBackground(Graphics graphics, Rectangle bounds, PushButtonState state, bool isDefault, Color backColor);
+    Rectangle DrawButtonBackground(Graphics graphics, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault, Color backColor);
 
     /// <summary>
     ///  Draws focus indicator appropriate for this style.

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/DarkMode/PopupButtonDarkModeRenderer.cs

@@ -30,11 +30,11 @@ internal class PopupButtonDarkModeRenderer : ButtonDarkModeRendererBase
     /// <summary>
     ///  Draws button background with popup styling, including subtle 3D effect.
     /// </summary>
-    public override Rectangle DrawButtonBackground(Graphics graphics, Rectangle bounds, PushButtonState state, bool isDefault, Color backColor)
+    public override Rectangle DrawButtonBackground(Graphics graphics, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault, Color backColor)
     {
         // Use padding from ButtonDarkModeRenderer
         Padding padding = PaddingCore;
-        Rectangle paddedBounds = Rectangle.Inflate(bounds, -padding.Left, -padding.Top);
+        Rectangle paddedBounds = Rectangle.Inflate(bounds, -1 - padding.Left, -1 - padding.Top);
 
         // Content rect will be used to position text and images
         Rectangle contentBounds = Rectangle.Inflate(paddedBounds, -padding.Left, -padding.Top);
@@ -52,9 +52,6 @@ public override Rectangle DrawButtonBackground(Graphics graphics, Rectangle boun
         using var brush = backColor.GetCachedSolidBrushScope();
         graphics.FillPath(brush, path);
 
-        // Draw 3D effect borders
-        DrawButtonBorder(graphics, paddedBounds, state, isDefault);
-
         // Return content bounds (area inside the button for text/image)
         return contentBounds;
     }
@@ -120,7 +117,7 @@ public override Color GetBackgroundColor(PushButtonState state, bool isDefault)
     /// <summary>
     ///  Draws the 3D effect border for the button.
     /// </summary>
-    private static void DrawButtonBorder(Graphics graphics, Rectangle bounds, PushButtonState state, bool isDefault)
+    public override void DrawButtonBorder(Graphics graphics, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault)
     {
         // Save original smoothing mode to restore later
         SmoothingMode originalMode = graphics.SmoothingMode;

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/DarkMode/SystemButtonDarkModeRenderer.cs

@@ -30,7 +30,7 @@ internal class SystemButtonDarkModeRenderer : ButtonDarkModeRendererBase
     /// <summary>
     ///  Draws button background with system styling (larger rounded corners).
     /// </summary>
-    public override Rectangle DrawButtonBackground(Graphics graphics, Rectangle bounds, PushButtonState state, bool isDefault, Color backColor)
+    public override Rectangle DrawButtonBackground(Graphics graphics, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault, Color backColor)
     {
         // Shrink for DarkBorderGap and FocusBorderThickness
         Rectangle fillBounds = Rectangle.Inflate(bounds, -SystemStylePadding, -SystemStylePadding);
@@ -108,6 +108,9 @@ public override Color GetBackgroundColor(PushButtonState state, bool isDefault)
                 _ => DefaultColors.StandardBackColor
             };
 
+    public override void DrawButtonBorder(Graphics graphics, Rectangle bounds, int borderSize, PushButtonState state, bool isDefault) =>
+        DrawButtonBorder(graphics, bounds, state, isDefault, false);
+
     /// <summary>
     ///  Draws the button border based on the current state, using anti-aliasing and an additional inner border.
     /// </summary>