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Change opacity without a round trip through HLC #16

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Merged
Jeehut merged 1 commit into from
Oct 15, 2026
Merged

Change opacity without a round trip through HLC #16

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13 changes: 4 additions & 9 deletions Sources/HandySwiftUI/Extensions/ColorExt.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -504,7 +504,7 @@ extension Color {
return self.change(attribute, to: self.hlco.chroma + addition)

case .opacity:
return self.change(attribute, to: self.hlco.opacity + addition)
return self.change(attribute, to: self.rgbo.opacity + addition)
}
}

Expand All @@ -516,13 +516,14 @@ extension Color {
/// - Returns: The resulting new `Color` with the specified change applied.
public func change(_ attribute: ChangeableAttribute, to newValue: Double) -> Self {
switch attribute {
case .red, .green, .blue:
case .red, .green, .blue, .opacity:
// Opacity is the same in every color space, so the RGB path changes it without a lossy round trip through HLC
return self.newRgboColor(attribute, newValue)

case .hueHSB, .saturation, .brightness:
return self.newHsboColor(attribute, newValue)

case .hueHLC, .luminance, .chroma, .opacity:
case .hueHLC, .luminance, .chroma:
return self.newHlcoColor(attribute, newValue)
}
}
Expand All @@ -540,9 +541,6 @@ extension Color {
case .chroma:
newHlco.chroma = newValue

case .opacity:
newHlco.opacity = newValue

default:
break
}
Expand All @@ -563,9 +561,6 @@ extension Color {
case .brightness:
newHsbo.brightness = newValue

case .opacity:
newHsbo.opacity = newValue

default:
break
}
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17 changes: 17 additions & 0 deletions Tests/HandySwiftUITests/ColorExtTests.swift
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Expand Up @@ -46,4 +46,21 @@ struct ColorExtTests {
// An in-gamut Display P3 color must be converted, not reported with its raw P3 components (which would be "80CC4D")
#expect(Color(.displayP3, red: 0.5, green: 0.8, blue: 0.3).toHex() == "64CE2F")
}

@Test(arguments: [(1.0, 0.0, 0.5), (0.2, 0.4, 0.6), (0.0, 1.0, 0.0)])
func changingOpacityKeepsTheRGBComponents(red: Double, green: Double, blue: Double) {
let color = Color(red: red, green: green, blue: blue)

// Float precision of the platform colors allows for deviations around 1e-7, the HLC round trip caused around 1e-6
func expectSameRGB(_ changed: (red: Double, green: Double, blue: Double, opacity: Double), opacity: Double) {
let tolerance = 0.000_000_5
#expect(abs(changed.red - color.rgbo.red) < tolerance)
#expect(abs(changed.green - color.rgbo.green) < tolerance)
#expect(abs(changed.blue - color.rgbo.blue) < tolerance)
#expect(abs(changed.opacity - opacity) < tolerance)
}

expectSameRGB(color.change(.opacity, to: 0.5).rgbo, opacity: 0.5)
expectSameRGB(color.change(.opacity, by: -0.25).rgbo, opacity: 0.75)
}
}
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