DarkMode (b) DarkModeButtonRenderer

[KlausLoeffelmann]

Add a DarkModeButton Renderer based on our existing ButtonFlatRenderer.

This way, we are getting completely independing of the XP-based VisualStyle rendering (and most of all incomplete theming for certain situations, like the Button rendering for 96DPI/100% scaling scenarios).

Fixes #11949.

Note:
The current DarkMode PRs need to be tested as a whole, so they are always rebased on each other, hence the "sorting" letters in the PR titles.

Since each of them carries from a review point of view every change of also of the one, the respective next is based on, I pushed also the "based-on PRs" as branches to the main repo, and had GitHub the PRs to review based on them, so you will ONLY see the changes for that particular PR.

Approach

TL;DR
Four sub-renderers are needed to faithfully reproduce the visual and interactive nuances of each FlatStyle in dark mode, ensuring both compatibility and a polished user experience.

The ButtonDarkModeRenderer is designed to render buttons with a modern, dark-themed appearance, while preserving the flexibility and compatibility required by the classic WinForms Button control. It achieves this by abstracting the rendering logic into a set of interchangeable renderer classes, each tailored to a specific FlatStyle.

Why Four Different Sub-Renderers?

WinForms Button supports four FlatStyle values, each with distinct visual and behavioral requirements. It was the goal, to find appropriate equivalents for each style in dark mode.

• Standard: Classic button with system-like appearance.
• Flat: Minimalist, border-only button with no background fill.
• Popup: Button with a subtle 3D effect, often used for toolbars or context menus.
• System: Used to delegate the rendering to the VisualStyle OS-calls for a native look. We have replaced this, to get closer to the style, that the Fluent Style does for WPF and how WinUI renders Buttons.

Each style has unique needs for borders, backgrounds, focus cues, and interaction feedback. To provide accurate dark mode support for all these styles, the renderer system uses four sub-renderers classes:

1. StandardButtonDarkModeRenderer
   Handles the default look, with subtle visual effects for Mouse hover and click.

2. FlatButtonDarkModeRenderer
   Renders a border-only button, with minimal effects and minimal background coloring, matching the original, minimalistic flat style.

3. PopupButtonDarkModeRenderer
   Provides a subtle 3D effect with rounded corners and shadow/highlight borders, suitable for popup-style buttons.

4. SystemButtonDarkModeRenderer
   Mimics the Fluent Style for WPF and how WinUI renders Buttons.

CodeFlow

• The main ButtonDarkModeRenderer selects the appropriate sub-renderer based on the button’s FlatStyle.
• Each sub-renderer implements a common interface (IButtonDarkModeRenderer) with methods for drawing the background, focus indicator, and determining text color.
• The sub-renderers encapsulate all style-specific logic, such as border thickness, corner radius, color selection, and focus cues.
• This separation ensures that each button style is rendered accurately in dark mode, while keeping the code maintainable and extensible.

Summary Table

FlatStyle	Renderer	Key Features in Dark Mode
Standard	StandardButtonDarkModeRenderer	3D borders, classic look, dark colors
Flat	FlatButtonDarkModeRenderer	Minimal border, hover/press feedback
Popup	PopupButtonDarkModeRenderer	Subtle 3D, rounded corners, shadow lines
System	SystemButtonDarkModeRenderer	WinUI look and feel.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 12.64546% with 1126 lines in your changes missing coverage. Please review.

Project coverage is 76.48147%. Comparing base (c78c1e9) to head (b83e93b).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13408         +/-   ##
===================================================
- Coverage   76.60074%   76.48147%   -0.11928%     
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  Files           3230        3239          +9     
  Lines         639097      640227       +1130     
  Branches       47289       47402        +113     
===================================================
+ Hits          489553      489655        +102     
- Misses        145962      146996       +1034     
+ Partials        3582        3576          -6     

Flag	Coverage Δ
Debug	76.48147% <12.64546%> (-0.11928%)	⬇️
integration	18.73882% <5.04267%> (-0.04191%)	⬇️
production	50.83950% <12.64546%> (-0.16490%)	⬇️
test	97.40411% <ø> (ø)
unit	48.24382% <12.64546%> (-0.17106%)	⬇️

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