Add LinearGradient

[Dark-Existed]

Block by OpenSwiftUICore.LinearGradient._Paint swift_dynamicCast related

[augmentcode]

🤖 Augment PR Summary

Summary: This PR introduces first-class gradient infrastructure and a new LinearGradient paint/style implementation.

Changes:

• Adds Gradient, AnyGradient, and a richer ResolvedGradient model (including color-space conversion and animatable vector support)
• Introduces a Paint/ResolvedPaint abstraction and an AnchoredResolvedPaint wrapper to carry bounds through resolution/drawing
• Implements LinearGradient as a Paint + View, drawing via GraphicsContext gradient shading
• Extends GraphicsContext.ResolvedShading to support gradients (geometry + option set)
• Updates shape-style packing/rendering to store/animate linear-gradient paints and to resolve gradients from a ShapeStyle
• Updates AnyShapeStyle to preserve AnyGradient providers
• Improves Color.Resolved animation data to support perceptual-space interpolation when enabled

Technical Notes: The new gradient pipeline relies on ResolvedPaint visitor/casting for animatable fill reconstruction and on ResolvedGradientVector for gradient interpolation.

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[augmentcode]

Review completed. 4 suggestions posted.

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[augmentcode]

Sources/OpenSwiftUICore/Graphic/Gradient/GradientColorSpace.swift:51: ColorSpaceGradientProvider.resolve currently returns base.resolve(in:) without applying colorSpace, so calling .colorSpace(_:) has no effect on the resulting ResolvedGradient.

Severity: medium

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[augmentcode]

Sources/OpenSwiftUICore/Graphic/Color/Paint.swift:154: AnchoredResolvedPaint doesn’t override resolvedGradient, so wrapping a gradient paint with bounds makes AnyResolvedPaint.resolvedGradient become nil (and also prevents visitors that cast to LinearGradient._Paint from matching the underlying paint type).

Severity: high

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[augmentcode]

Sources/OpenSwiftUICore/Graphic/Gradient/Gradient.swift:425: ResolvedGradientVector.setColorSpace converts using colorSpace.convertOut(...) on an InterpolatableColor that is still encoded in the previous self.colorSpace, which likely corrupts colors when mixing/animating gradients across different color spaces.

Severity: medium

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[augmentcode]

Sources/OpenSwiftUICore/Graphic/Gradient/Gradient.swift:384: In add(_ other:scaledBy:), the Bezier timing-function components apply scale to li (lhs) rather than ri (rhs), so lhs += rhs * scale behaves incorrectly for stop interpolations during animation.

Severity: medium

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