Pre-composite backdrop

[lawrencecchen]

Summary by cubic

Pre-composites the tab bar pane background over the window background and uses the flat color for the split-button backdrop. This removes double-compositing mismatches so the overlay matches the bar fill in both focused and unfocused states.

^{Written for commit 07e8fa0. Summary will update on new commits.}

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 33e772ac-3568-4ce7-ac9a-bd564a5be1e2

📥 Commits

Reviewing files that changed from the base of the PR and between 21626d5 and 07e8fa0.

📒 Files selected for processing (1)

• Sources/Bonsplit/Internal/Views/TabBarView.swift

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch hstack-sibling-buttons

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[cubic-dev-ai]

No issues found across 1 file

[greptile-apps]

Greptile Summary

This PR refactors the pre-compositing logic for the split-button backdrop from an inline closure in the view body into a reusable private static func precompositedPaneBackground(for:focused:) -> NSColor. The intent — flattening the translucent pane chrome over the window background to avoid double-compositing — is preserved. However, the extracted function inadvertently changes the color space of the returned NSColor from sRGB (original: NSColor(sRGBRed:…)) to calibrated RGB (new: NSColor(red:…)), even though the blended component values are computed in the sRGB space.

• The refactor improves readability and reusability of the compositing math.
• Regression: Line 546 uses NSColor(red:green:blue:alpha:) (creates an NSCalibratedRGBColorSpace color) instead of NSColor(sRGBRed:green:blue:alpha:) (sRGB). Because r, g, b are computed as sRGB values, wrapping them in a calibratedRGB color is semantically incorrect and partially defeats the purpose of this PR.

Confidence Score: 3/5

• Not safe to merge as-is — the color-space regression partially reintroduces the compositing mismatch this PR intends to fix.
• There is one clear P1 regression: the extracted static function uses NSColor(red:green:blue:alpha:) (calibratedRGB) instead of NSColor(sRGBRed:green:blue:alpha:) (sRGB). The blended values are sRGB-space, so packaging them as calibratedRGB produces a subtly wrong color, undoing the core goal of the PR. The fix is a one-word change on a single line.
• Sources/Bonsplit/Internal/Views/TabBarView.swift — line 546, the NSColor initializer.

Important Files Changed

Filename	Overview
Sources/Bonsplit/Internal/Views/TabBarView.swift	Refactors the inline pre-compositing closure into a reusable static func precompositedPaneBackground(for:focused:), but introduces a regression: NSColor(red:green:blue:alpha:) (calibratedRGB) is used instead of the original NSColor(sRGBRed:green:blue:alpha:) (sRGB), mismatching the color space of the blended components.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["View body: showSplitButtons == true"] --> B["Call Self.precompositedPaneBackground(for: appearance, focused: isFocused)"]
    B --> C["Get chrome = TabBarColors.nsColorPaneBackground(for: appearance)"]
    B --> D["Get winBg = NSColor.windowBackgroundColor"]
    C & D --> E{"Convert both to .sRGB"}
    E -- "conversion fails" --> F["Return chrome.withAlphaComponent(1.0)"]
    E -- "success: fg, bk" --> G["Compute alpha 'a'\n(focused ? fg.alpha : fg.alpha × 0.95)"]
    G --> H["Blend: r/g/b = fg×a + bk×(1−a)"]
    H --> I["⚠️ NSColor(red:green:blue:alpha:)\ncalibratedRGB — should be sRGBRed:"]
    I --> J["Color(nsColor:) → SwiftUI Color 'bg'"]
    J --> K["LinearGradient + Rectangle backdrop\nusing 'bg'"]
    K --> L["ZStack: backdrop + splitButtons overlay"]

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[greptile-apps]

Wrong NSColor initializer changes color space from sRGB to calibratedRGB

The extracted function blends components after converting both inputs to .sRGB (lines 537–538), so r, g, and b are sRGB-space values. The original inline code used NSColor(sRGBRed:green:blue:alpha:) to correctly wrap those values back into the sRGB color space.

The new code uses NSColor(red:green:blue:alpha:), which creates an NSCalibratedRGBColorSpace color — a different color space. The same numeric component values interpreted in calibrated RGB will render at a slightly different color than intended, reintroducing the compositing mismatch the PR aims to fix.

Suggested change

	return NSColor(red: r, green: g, blue: b, alpha: 1.0)
	return NSColor(sRGBRed: r, green: g, blue: b, alpha: 1.0)