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Interpolation

Runtime API surface for scripted interpolation.

Runtime baseline

This page reflects npm runtime line 2.37.6 with upstream source snapshot runtime-v0.1.64 (b25a322, audited May 12, 2026).

ScriptedInterpolator​

ScriptedInterpolator is a runtime-backed protocol used to customize interpolation/easing behavior.

Callback contract​

export type ScriptedInterpolator<T> = {
    init: ((self: T, context: Context) -> boolean)?,
    transform: ((self: T, factor: number) -> number)?,
    transformValue: ((self: T, valueFrom: number, valueTo: number, factor: number) -> number)?,
} & T

Methods​

transform(self, factor)​

Optional factor remapping hook.

transform(self: T, factor: number): number

transformValue(self, valueFrom, valueTo, factor)​

Optional direct value interpolation hook.

transformValue(self: T, valueFrom: number, valueTo: number, factor: number): number

Runtime fallback behavior​

If either callback is missing or errors:

  • transform falls back to the input factor unchanged.
  • transformValue falls back to linear interpolation (from + (to - from) * factor).

Example​

export type EaseInOut = {
    strength: Input<number>,
}

local function smoothstep(t: number): number
    return t * t * (3 - 2 * t)
end

function transform(self: EaseInOut, factor: number): number
    local t = math.max(0, math.min(1, factor))
    return smoothstep(t)
end

function transformValue(self: EaseInOut, valueFrom: number, valueTo: number, factor: number): number
    local t = transform(self, factor)
    return valueFrom + (valueTo - valueFrom) * t
end

return function(): ScriptedInterpolator<EaseInOut>
    return {
        transform = transform,
        transformValue = transformValue,
        strength = 1,
    }
end