implement-upstream-port

name	implement-upstream-port
description	Port a feature from an upstream library into Kotlin Multiplatform code in the Krayon repo. Use when the user asks to implement, add, or port a feature from an external library (D3, Vega, Apache Commons Math, etc.) into a Krayon module.

Implement Upstream Port

Translate an upstream library's implementation into idiomatic Kotlin for Krayon.

Prerequisites

If you don't already have a clear understanding of the upstream feature's API and algorithm, use the research-upstream-api skill first.

Krayon-specific patterns

• Float, not Double: Krayon uses Float throughout. Convert upstream numeric types accordingly.
• PathBuilder: drawing code emits commands via PathBuilder<*>. Key methods: moveTo, lineTo, cubicTo, quadraticTo, close.
• Curve interface: new curves implement com.juul.krayon.shape.curve.Curve with startArea, endArea, startLine, endLine, point.
• Parameterized features: upstream builder/factory configuration (e.g. D3's cardinal.tension(t)) becomes constructor parameters with matching default values.
• State management: mirror upstream instance variables as private var properties, reset in the appropriate lifecycle method (e.g. startLine).

JS/D3 translation cheat sheet

JS / D3	Krayon (Kotlin)
export default function Foo	public class Foo : <Interface>
Closure-captured mutable state	Private mutable properties on the class
NaN sentinel for "not set"	Float.NaN — use a truthy() helper
context.bezierCurveTo(a,b,c,d,e,f)	context.cubicTo(a,b,c,d,e,f)

The existing Linear.kt has a private Float.truthy() extension for JS truthiness semantics. Reuse this when porting code that checks NaN/0 as boolean.

After implementing

1. Run ./gradlew lintKotlin and fix any formatting issues.
2. Run ./gradlew apiDump to regenerate API signature files.
3. Update the repo-root NOTICE file to credit the upstream library (see existing entries for the format).
4. Write tests (see the write-krayon-tests skill).