Fix DarkMode (a) StatusStrip background renderer A11Y Regression. #13360

KlausLoeffelmann · 2025-04-23T21:43:46Z

Fixes #12909.
Fixes #12663.
Fixes #12041.
Fixes #12040.
Fixes #12027.

As for the approach.
We already have a series of Renderers, where we need to avoid passing rendering down to the visual styles. In fact, for the ToolStrip and everything around it, we do most of the render work ourselves.

That also means, we're in many cases no longer compatible with subtle details. The rounded corners of the Windows 11 windows for example, can obscure the symbolic Grip, depending on the Window border color and the resulting Antialias, and leave not enough distance for a good contrast:

And then in addition, since we have WAY higher resolutions since back then, we also needed a bigger area for better contrast and visibility. This change addresses that, and also reposition the grip pixel to follow the shape of the rounded corners:

Microsoft Reviewers: Open in CodeFlow

codecov · 2025-04-23T22:17:11Z

Codecov Report

Attention: Patch coverage is 24.91639% with 449 lines in your changes missing coverage. Please review.

Project coverage is 76.56041%. Comparing base (380e851) to head (19fc0c4).
Report is 21 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13360         +/-   ##
===================================================
- Coverage   76.60904%   76.56041%   -0.04863%     
===================================================
  Files           3236        3237          +1     
  Lines         639448      639896        +448     
  Branches       47318       47380         +62     
===================================================
+ Hits          489875      489907         +32     
- Misses        146048      146455        +407     
- Partials        3525        3534          +9

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production	`50.94548% <24.91639%> (-0.06844%)`	⬇️
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Copilot

Pull Request Overview

This PR addresses several A11Y regressions related to DarkMode rendering by removing experimental diagnostic attributes and refining related rendering logic. Key changes include the removal of experimental DarkMode attributes in form APIs, the introduction and integration of a dedicated dark mode renderer in ToolStripSystemRenderer, and various rendering improvements in ToolStripRenderer and StatusStrip.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
FormCornerPreference.cs	Removed experimental diagnostic attribute for DarkMode support.
Form.cs	Removed experimental attribute on DarkMode–related properties and events.
ToolStripSystemRenderer.cs	Introduced a dedicated dark mode renderer and updated RendererOverride logic.
ToolStripRenderer.cs	Updated rendering paths and optimized array initializations for DarkMode disabled images.
ToolStrip.cs	Modified background painting to use renderer overrides when available.
StatusStrip.cs	Updated comment spelling for clarity.
PublicAPI.Unshipped.txt	Updated API documentation entries for FormCornerPreference and related events.

Comments suppressed due to low confidence (6)

src/System.Windows.Forms/System/Windows/Forms/FormCornerPreference.cs:11

Verify that the removal of the experimental DarkMode diagnostic attribute is intended and that any related tooling or documentation has been updated accordingly.

-[Experimental(DiagnosticIDs.ExperimentalDarkMode, UrlFormat = DiagnosticIDs.UrlFormat)]

src/System.Windows.Forms/System/Windows/Forms/Form.cs:2185

Ensure that removing the experimental attribute from the Form properties aligns with production readiness for DarkMode, and update any related diagnostic handling as needed.

-    [Experimental(DiagnosticIDs.ExperimentalDarkMode, UrlFormat = DiagnosticIDs.UrlFormat)]

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/StatusStrip.cs:121

Correct the spelling of 'accomodate' to 'accommodate' in the comment for clarity.

// we do some custom stuff with padding to accomodate size grip.

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripSystemRenderer.cs:18

Confirm that prioritizing high contrast mode over dark mode in the RendererOverride is intended and that the newly introduced dark mode renderer meets accessibility guidelines.

+    private ToolStripRenderer? _toolStripDarkModeRenderer;

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripRenderer.cs:855

Review the logic change for rendering item check images to ensure that returning early when the image rectangle is empty or the image is null does not inadvertently skip intended rendering in edge cases.

+        if (imageRect == Rectangle.Empty || image is null)

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStrip.cs:3651

[nitpick] Ensure that using the renderer override to draw the ToolStrip background and returning early does not conflict with any custom rendering requirements that downstream consumers might have.

+            if (Renderer.RendererOverride is ToolStripRenderer renderer)

JeremyKuhne

Added comments. Please describe what changes you've made in your PR, not just what it will fix.

JeremyKuhne · 2025-05-09T20:07:29Z

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

@@ -546,24 +546,12 @@ public static bool VisualStylesEnabled

    internal static ToolStripRenderer CreateRenderer(ToolStripManagerRenderMode renderMode)
    {
-        switch (renderMode)
+        return renderMode switch


nit: you can turn this into => now.

JeremyKuhne · 2025-05-09T20:08:03Z

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

@@ -6,47 +6,83 @@

 namespace System.Windows.Forms;

+/// <summary>
+/// Provides system rendering for ToolStrip controls with support for dark mode.


Please indent all XML comments by a space.

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

JeremyKuhne · 2025-05-09T20:18:35Z

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

            }
            else if (toolStrip.IsDropDown)
            {
-                FillBackground(g, bounds, (!ToolStripManager.VisualStylesEnabled) ?
-                                     e.BackColor : SystemColors.Menu);
+                FillBackground(g, bounds, (!ToolStripManager.VisualStylesEnabled)


Reversing the ! would be clearer and the parenthesis isn't needed.

JeremyKuhne · 2025-05-09T20:51:09Z

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

-        new(8, 0, 2, 2),
+    private static readonly Rectangle[] s_baseSizeGripRectangles =
+    [
+        new(12, 0, 2, 2),


Why did these change?

See added screenshots for explanaition.

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

KlausLoeffelmann · 2025-05-12T06:30:27Z

Added comments.

@merriemcgaw, @Tanya-Solyanik, @Shyam-Gupta:

First of all, @jeremy, thanks for the review!

While reading @JeremyKuhne review comments, I got the idea, that many of his comments can be in fact generelized Copilot instructions, which we could just "run" before we submit a PR. I think that would drastically reduce the workload, both for review and for keeping all those little optinization details in mind, and we could actually concentrate more on the domain-specific work.

I created #13441, and my suggestion would be, that if someone sees an optimization potential, which would also work in a generic way, that they not only comment, but also add those to a list of general CoPilot instructions. This list can grow over time, and will exponentially save time, with this kind of work.

What do y'all think?

I have experimented over the weekend with a few approaches, and I think this looks promesing.
I have in this case created a document based on Jeremie's comments and will spend one or two hours tomorrow to see, if I can address half of the issues "in one go" so to say.

memoarfaa

Recording.2025-05-13.030723.mp4

@KlausLoeffelmann
@JeremyKuhne
Why not just to be

    private static void RenderStatusStripBackground(ToolStripRenderEventArgs e)
    {
        if (Application.RenderWithVisualStyles)
        {
            VisualStyleRenderer vsRenderer = VisualStyleRenderer!;
#pragma warning disable WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
            VisualStyleElement visualStyleElement = Application.IsDarkModeEnabled
                ? VisualStyleElement.CreateElement("DarkMode::ExplorerStatusBar", 0, 0)
                : VisualStyleElement.Status.Bar.Normal;
#pragma warning restore WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
            ;

            vsRenderer.SetParameters(visualStyleElement);
            vsRenderer.DrawBackground(e.Graphics, new Rectangle(0, 0, e.ToolStrip.Width - 1, e.ToolStrip.Height - 1));
        }
        else
        {
            if (!SystemInformation.InLockedTerminalSession())
            {
                e.Graphics.Clear(e.BackColor);
            }
        }
    }

Can you use Dark Mode Render instead of accessibility drawing please?

KlausLoeffelmann · 2025-05-13T01:42:06Z

Images aren't very a11y-friendly, the text could have been copied and pasted in.

Hey @RussKie,

I cannot see the screenshot you assumingly posted - can you fix that?

Also, the plan is:
we want to get the Renderer quickly out for Preview 5, so we can all test and refine.

…pilot Instruction files.

…background painting.

JeremyKuhne

There is more feedback to address (maybe an hour or so of work), but nothing that blocks getting this in for the next preview. Approving with the understanding that we'll address with a follow up issue to track.

JeremyKuhne · 2025-06-16T17:29:03Z

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

+        Color arrowColor)
+    {
+        ArgumentNullException.ThrowIfNull(e);
+
        Graphics g = e.Graphics;


FYI: I've created an issue to re-do the GraphicsInternal stuff: #13604

JeremyKuhne · 2025-06-16T17:34:25Z

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

-        // We need to check for null here, since at design time at this point Item can be null.
-        if (e.Item is not null && e.Item.DeviceDpi != _previousDeviceDpi && ScaleHelper.IsThreadPerMonitorV2Aware)
+        // Scale arrow offsets if needed
+        if (e.Item is not null


nit: I know this was this way, but as you did change the code here, this would be better with pattern matching. Also, why are we dropping the comment about design time?

JeremyKuhne · 2025-06-16T17:47:27Z

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

-                    greyRectangles[i] = baseRect;
-                }
+            // Apply scaling
+            g.ScaleTransform(heightScale, heightScale);


Just a general comment here. In the future, if we want to fine tune for performance, we should consider scaling the rectangles and points directly. This is particularly true when it comes to us trying to directly GDI render on the Graphics object as we'll be able to assert that we don't need to extract state. (See GraphicsInternal discussions)

JeremyKuhne · 2025-06-16T17:50:40Z

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

+            // Default offset
+            int offset = 2;
+
+            if (Environment.OSVersion.Version >= new Version(10, 0, 22000)


This warrants a comment about what version this is and what changed exactly. Also, what will the impact be to user perceived rendering be if the OS changes again?

JeremyKuhne · 2025-06-16T17:56:05Z

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

-    {
-        return (control.RawBackColor == Color.Empty && control.BackgroundImage is null);
-    }
+    // Only paint background effects if no BackColor has been set


Part of the reason for this is that comments on the outside become the IntelliSense docs for the method. ShouldPaintBackground is pretty self-explanatory, but if there was a <summary> comment it shouldn't explain the implementation details. Not a huge deal, but you did change the code here for style, so it was worth pointing out.

JeremyKuhne · 2025-06-16T17:57:59Z

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

+///   and overrides necessary methods to provide dark-themed rendering.
+///   </para>
+/// </remarks>
+internal class ToolStripSystemDarkModeRenderer : ToolStripRenderer


No, it would not be a binary breaking change. It does, however, have an impact on performance to leave it unsealed. The JIT can better de-virtualize when classes are sealed.

JeremyKuhne · 2025-06-16T18:02:48Z

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

+    private static Color GetDarkModeColor(Color color) =>
+        color switch
+        {
+            Color c when c == SystemColors.Control => Color.FromArgb(45, 45, 45),


This would be much more efficient to switch on color.ToKnownColor().

JeremyKuhne · 2025-06-16T18:04:10Z

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

+        Graphics g = e.Graphics;
+        Rectangle bounds = e.AffectedBounds;
+
+        if (!ShouldPaintBackground(toolStrip))


I've created an issue on GraphicsInternal optimization and mentioned it elsewhere.

KlausLoeffelmann · 2025-06-16T20:55:46Z

@JeremyKuhne, @merriemcgaw:
Tracking the important parts here at one central point, so they do not get lost.

#13605

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[Umbrella] Collect optimization Suggestions/Ideas and phrase out CoPilot Instructions for actually doing the optimization work #13441

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KlausLoeffelmann added 5 commits June 14, 2025 09:58

Fix DarkMode StatusStrip background renderer.

4a29a8f

Implement ToolStripSystemDarkModeRenderer.

97a5e9f

Fix the StatusStripSizingGrip.

8cf4568

Change Grip renderer to use predefined shape.

a0277bd

First batch of addressed review suggestions.

377da34

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KlausLoeffelmann added 3 commits June 14, 2025 21:36

Refactor ToolStripRenderer classes and improve generic and GDIPlus Co…

25e40ae

…pilot Instruction files.

Fix existing bug in GripSize calculation in HighDPI.

a6436aa

Fix bug where a dedicated Toolstrip Renderer would not be called for …

933b263

…background painting.

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Fix merge issues.

fa13f5e

Address review suggestions.

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[Tracking] Important manually review work for DarkMode for Preview 7 #13605

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Olina-Zhang mentioned this pull request Jun 19, 2025

DemoConsole app: An exception pops up when focusing on "Type Here" in contextMenuStrip under DarkMode #13624

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Fix DarkMode (a) StatusStrip background renderer A11Y Regression. #13360

Fix DarkMode (a) StatusStrip background renderer A11Y Regression. #13360

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