First batch of addressed review suggestions.

Author: KlausLoeffelmann

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStrip.cs

@@ -1549,7 +1549,7 @@ public ToolStripRenderMode RenderMode
                 return ToolStripRenderMode.ManagerRenderMode;
             }
 
-            if (_renderer is not null && !_renderer.IsAutoGenerated)
+            if (_renderer is not null && !_renderer.IsSystemDefaultAlternative)
             {
                 return ToolStripRenderMode.Custom;
             }

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripManager.cs

@@ -489,7 +489,7 @@ public static ToolStripManagerRenderMode RenderMode
         {
             Type currentType = CurrentRendererType;
 
-            if (t_defaultRenderer is not null && !t_defaultRenderer.IsAutoGenerated)
+            if (t_defaultRenderer is not null && !t_defaultRenderer.IsSystemDefaultAlternative)
             {
                 return ToolStripManagerRenderMode.Custom;
             }

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripRenderer.cs

@@ -37,7 +37,7 @@ public abstract class ToolStripRenderer
     private static ColorMatrix? s_disabledImageColorMatrix;
 
     private EventHandlerList? _events;
-    private readonly bool _isAutoGenerated;
+    private readonly bool _isSystemDefaultAlternative;
 
     private static bool s_isScalingInitialized;
     internal int _previousDeviceDpi = ScaleHelper.InitialSystemDpi;
@@ -52,28 +52,12 @@ public abstract class ToolStripRenderer
     private static int s_offset4X = OFFSET_4PIXELS;
     private static int s_offset4Y = OFFSET_4PIXELS;
 
-    // Used in building up the half pyramid of rectangles that are drawn in a
-    // status strip sizing grip.
-    private static readonly Rectangle[] s_baseSizeGripRectangles =
-    [
-        new(12, 0, 2, 2),
-        new(8, 4, 2, 2),
-        new(4, 8, 2, 2),
-        new(0, 12, 2, 2),
-        new(8, 0, 2, 2),
-        new(4, 4, 2, 2),
-        new(0, 8, 2, 2),
-        new(4, 0, 2, 2),
-        new(0, 4, 2, 2),
-        new(1, 1, 2, 2),
-    ];
-
     protected ToolStripRenderer()
     {
     }
 
     internal ToolStripRenderer(bool isAutoGenerated) =>
-        _isAutoGenerated = isAutoGenerated;
+        _isSystemDefaultAlternative = isAutoGenerated;
 
     // Used in building disabled images.
     private static ColorMatrix DisabledImageColorMatrix
@@ -153,7 +137,13 @@ private EventHandlerList Events
         }
     }
 
-    internal bool IsAutoGenerated => _isAutoGenerated;
+    /// <summary>
+    ///  Defines, if there is a variation of the system default renderer, that is chosen by the system
+    ///  to address the current environment context. Like DarkMode, HighContrast, LowRes etc.
+    ///  (Used to be 'AutoGenerated', presuming to indicate, that the renderer was 'generated' (picked) by the system.)
+    /// </summary>
+    internal bool IsSystemDefaultAlternative
+        => _isSystemDefaultAlternative;
 
     // if we're in a low contrast, high resolution situation, use this renderer under the covers instead.
     internal virtual ToolStripRenderer? RendererOverride => null;
@@ -1012,39 +1002,57 @@ protected virtual void OnRenderToolStripStatusLabelBackground(ToolStripItemRende
         }
     }
 
+    // Used in building up the half pyramid of rectangles that are drawn in a
+    // status strip sizing grip.
+    private static readonly Rectangle[] s_baseSizeGripRectangles =
+    [
+        new(12, 0, 2, 2),
+        new(8, 4, 2, 2),
+        new(4, 8, 2, 2),
+        new(0, 12, 2, 2),
+        new(8, 0, 2, 2),
+        new(4, 4, 2, 2),
+        new(0, 8, 2, 2),
+        new(4, 0, 2, 2),
+        new(0, 4, 2, 2),
+        new(1, 1, 2, 2),
+    ];
+
     protected virtual void OnRenderStatusStripSizingGrip(ToolStripRenderEventArgs e)
     {
         ArgumentNullException.ThrowIfNull(e);
 
+        if (RendererOverride is not null)
+        {
+            RendererOverride.OnRenderStatusStripSizingGrip(e);
+            return;
+        }
+
         OnRenderStatusStripSizingGrip(
             eArgs: e,
             highLightBrush: SystemBrushes.ButtonHighlight,
-            shadowBrush: SystemBrushes.ButtonShadow);
+            shadowBrush: SystemBrushes.GrayText);
     }
 
-    private protected void OnRenderStatusStripSizingGrip(
+    private protected static void OnRenderStatusStripSizingGrip(
         ToolStripRenderEventArgs eArgs,
         Brush highLightBrush,
         Brush shadowBrush)
     {
-        if (RendererOverride is not null)
-        {
-            RendererOverride.OnRenderStatusStripSizingGrip(eArgs);
-            return;
-        }
-
         if (eArgs.ToolStrip is not StatusStrip statusStrip)
         {
             return;
         }
 
         Rectangle sizeGripBounds = statusStrip.SizeGripBounds;
+
         if (LayoutUtils.IsZeroWidthOrHeight(sizeGripBounds))
         {
             return;
         }
 
         Graphics g = eArgs.Graphics;
+        ReadOnlySpan<Rectangle> baseRects = s_baseSizeGripRectangles;
 
         // Use device DPI for scaling
         float dpiScale = 1.0f;
@@ -1054,12 +1062,13 @@ private protected void OnRenderStatusStripSizingGrip(
             dpiScale = statusStrip.DeviceDpi / 96f;
         }
 
-        // Scale the base rectangles for the grip dots
-        Rectangle[] scaledRects = new Rectangle[s_baseSizeGripRectangles.Length];
+        // Create a buffer on the stack for the scaled rectangles
+        Span<Rectangle> scaledRects = stackalloc Rectangle[baseRects.Length];
 
-        for (int i = 0; i < s_baseSizeGripRectangles.Length; i++)
+        // Scale the base rectangles for the grip dots
+        for (int i = 0; i < baseRects.Length; i++)
         {
-            Rectangle r = s_baseSizeGripRectangles[i];
+            Rectangle r = baseRects[i];
 
             scaledRects[i] = new Rectangle(
                 (int)(r.X * dpiScale),
@@ -1074,40 +1083,49 @@ private protected void OnRenderStatusStripSizingGrip(
         SmoothingMode oldSmoothing = g.SmoothingMode;
         g.SmoothingMode = SmoothingMode.AntiAlias;
 
+        // Optimize for RTL check by determining the calculation function once
+        bool isRtl = statusStrip.RightToLeft == RightToLeft.Yes;
+
         // Draw the grip dots, bottom-right aligned (mirrored for RTL)
-        foreach (Rectangle dotRect in scaledRects)
+        Span<Rectangle> workingRects = stackalloc Rectangle[3]; // actualRect, highlightRect, shadowRect
+
+        for (int i = 0; i < scaledRects.Length; i++)
         {
-            Rectangle actualRect = statusStrip.RightToLeft == RightToLeft.Yes
+            ref Rectangle dotRect = ref scaledRects[i];
+            ref Rectangle actualRect = ref workingRects[0];
+            ref Rectangle highlightRect = ref workingRects[1];
+            ref Rectangle shadowRect = ref workingRects[2];
+
+            actualRect = isRtl
                 ? new Rectangle(
                     x: sizeGripBounds.Left + cornerOffset + dotRect.X,
                     y: sizeGripBounds.Bottom - cornerOffset - dotRect.Y - dotRect.Height,
                     width: dotRect.Width,
                     height: dotRect.Height)
-
                 : new Rectangle(
                     x: sizeGripBounds.Right - cornerOffset - dotRect.X - dotRect.Width,
                     y: sizeGripBounds.Bottom - cornerOffset - dotRect.Y - dotRect.Height,
                     width: dotRect.Width,
                     height: dotRect.Height);
 
             // Highlight dot (top-left)
-            Rectangle highlightRect = actualRect;
+            highlightRect = actualRect;
             highlightRect.Offset(-1, -1);
-
             g.FillEllipse(highLightBrush, highlightRect);
 
             // Shadow dot (bottom-right)
-            Rectangle shadowRect = actualRect;
+            shadowRect = actualRect;
             shadowRect.Offset(1, 1);
-
             g.FillEllipse(shadowBrush, shadowRect);
         }
 
         g.SmoothingMode = oldSmoothing;
 
+        // We need to account for Windows 11+ AND whatever styled corners we have.
         static (int cornerOffset, Rectangle rect) GetCornerOffset(StatusStrip statusStrip)
         {
-            (int, Rectangle) cornerDef = (2, new(1, 1, 2, 2));
+            // Default values
+            (int offset, Rectangle rect) cornerDef = (2, new(1, 1, 2, 2));
 
             if (Environment.OSVersion.Version >= new Version(10, 0, 22000)
                 && statusStrip.FindForm() is Form f)

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripRendererSwitcher.cs

@@ -80,7 +80,7 @@ public ToolStripRenderMode RenderMode
                 return ToolStripRenderMode.ManagerRenderMode;
             }
 
-            if (_renderer is not null && !_renderer.IsAutoGenerated)
+            if (_renderer is not null && !_renderer.IsSystemDefaultAlternative)
             {
                 return ToolStripRenderMode.Custom;
             }

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripSystemDarkModeRenderer.cs

@@ -27,8 +27,12 @@ public ToolStripSystemDarkModeRenderer()
     /// <summary>
     ///  Initializes a new instance of the ToolStripSystemDarkModeRenderer class with the specified default state.
     /// </summary>
-    /// <param name="isDefault">true if this is the default renderer; otherwise, false.</param>
-    internal ToolStripSystemDarkModeRenderer(bool isDefault) : base(isDefault)
+    /// <param name="isSystemDefaultAlternative">
+    ///  True if this should be seen as a variation of the default renderer
+    ///  (so, no _custom_ renderer provided by the user); otherwise, false.
+    /// </param>
+    internal ToolStripSystemDarkModeRenderer(bool isSystemDefaultAlternative)
+        : base(isSystemDefaultAlternative)
     {
     }
 
@@ -171,7 +175,7 @@ protected override void OnRenderToolStripBackground(ToolStripRenderEventArgs e)
     ///  Renders the StatusStrip background in dark mode.
     /// </summary>
     /// <param name="e">A ToolStripRenderEventArgs that contains the event data.</param>
-    private static void RenderStatusStripBackground(ToolStripRenderEventArgs e)
+    internal static void RenderStatusStripBackground(ToolStripRenderEventArgs e)
     {
         Graphics g = e.Graphics;
         Rectangle bounds = e.AffectedBounds;

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripSystemRenderer.cs

@@ -39,7 +39,7 @@ internal ToolStripRenderer HighContrastRenderer
     {
         get
         {
-            _toolStripHighContrastRenderer ??= new ToolStripHighContrastRenderer(systemRenderMode: false);
+            _toolStripHighContrastRenderer ??= new ToolStripHighContrastRenderer(systemRenderMode: true);
             return _toolStripHighContrastRenderer;
         }
     }
@@ -51,7 +51,7 @@ internal ToolStripRenderer DarkModeRenderer
     {
         get
         {
-            _toolStripDarkModeRenderer ??= new ToolStripSystemDarkModeRenderer(isDefault: false);
+            _toolStripDarkModeRenderer ??= new ToolStripSystemDarkModeRenderer(isSystemDefaultAlternative: true);
             return _toolStripDarkModeRenderer;
         }
     }
@@ -218,6 +218,18 @@ private static ToolBarState GetToolBarState(ToolStripItem item)
     /// </summary>
     protected override void OnRenderToolStripBackground(ToolStripRenderEventArgs e)
     {
+        // It is not entirely clear, why we're not leaving it to the respective renderers
+        // what to do here, but for keeping as much as possible of the original behavior,
+        // we need to check if the renderer override is set, test for particular renderer types
+        // and then decide what to do.
+        if (RendererOverride is ToolStripSystemDarkModeRenderer darkModeRenderer
+            && darkModeRenderer.IsSystemDefaultAlternative)
+        {
+            base.OnRenderToolStripBackground(e);
+
+            return;
+        }
+
         ToolStrip toolStrip = e.ToolStrip;
         Graphics g = e.Graphics;
         Rectangle bounds = e.AffectedBounds;
@@ -240,18 +252,18 @@ protected override void OnRenderToolStripBackground(ToolStripRenderEventArgs e)
             else if (DisplayInformation.LowResolution)
             {
                 FillBackground(g, bounds, (toolStrip is ToolStripDropDown)
-                    ? e.BackColor
-                    : SystemColors.ControlLight);
+                     ? SystemColors.ControlLight
+                     : e.BackColor);
             }
             else if (toolStrip.IsDropDown)
             {
-                FillBackground(g, bounds, (!ToolStripManager.VisualStylesEnabled)
+                FillBackground(g, bounds, ToolStripManager.VisualStylesEnabled
                     ? SystemColors.Menu
                     : e.BackColor);
             }
             else if (toolStrip is MenuStrip)
             {
-                FillBackground(g, bounds, (!ToolStripManager.VisualStylesEnabled)
+                FillBackground(g, bounds, ToolStripManager.VisualStylesEnabled
                     ? SystemColors.MenuBar
                     : e.BackColor);
             }
@@ -264,9 +276,9 @@ protected override void OnRenderToolStripBackground(ToolStripRenderEventArgs e)
             }
             else
             {
-                FillBackground(g, bounds, (!ToolStripManager.VisualStylesEnabled)
-                    ? e.BackColor
-                    : SystemColors.MenuBar);
+                FillBackground(g, bounds, ToolStripManager.VisualStylesEnabled
+                    ? SystemColors.MenuBar
+                    : e.BackColor);
             }
         }
     }