API
Babylon Lite|
Architecture|
Inverse Lerp

Module: Bounded inverse interpolation

Package path: packages/babylon-lite/src/math/inverse-lerp.ts

Purpose and public API

export function inverseLerp(a: number, b: number, value: number): number;

Import inverseLerp from @babylonjs/lite. It calculates the parameter of value between endpoints a and b, clamped to [0, 1], matching Babylon.js Scalar.InverseLerp. Both increasing and decreasing intervals are supported.

Algorithm and state

If a === b, return 0. Otherwise compute (value - a) / (b - a) and clamp with Math.min(1, Math.max(0, parameter)). The first endpoint yields 0 and the second yields 1; values outside the interval saturate according to endpoint order. Non-finite inputs follow ordinary JavaScript arithmetic, including propagation of NaN from an indeterminate ratio.

The function is pure and allocates nothing. It has no dependencies, import-time initialization, caches, ownership or lifecycle. GPU pipelines and shaders do not apply. Existing Lerp and Normalize semantics are unchanged.

Compatibility and isolation

Compat Scalar.InverseLerp(a, b, value) forwards to the native root helper without implementing the math. The public names/signatures are preserved; only the incorrect extrapolation outside the interval is corrected. Unused native imports must disappear completely from a consumer bundle.

Test specification

  • Direct native tests cover both interval directions, interior/endpoints, outside-range saturation and degenerate intervals.
  • Compat regression/control cases verify the Babylon.js-shaped forwarding API against expected outputs.
  • Removing either bound must fail corresponding regressions.
  • A root import exposes the helper without engine or GPU entry points; an unused import emits identical code.
  • Full declarations, lint/types and focused native scene byte controls preserve the existing public/footprint contracts.

File manifest

math/inverse-lerp.ts, native root index.ts, compat math/scalar.ts, native unit/build tests, compat math tests, this contract and the Scalar support row.