feat(math): lerp and remap utils (#31)

src/math.test.ts

@@ -1,5 +1,5 @@
 import { expect, it } from 'vitest'
-import { sum } from './math'
+import { lerp, remap, sum } from './math'
 
 it('sum', () => {
   expect(sum(1, 2, 3)).toEqual(6)
@@ -9,3 +9,27 @@ it('sum', () => {
   // @ts-expect-error
   expect(sum(1, 2, [1, 2, 3])).toEqual(9)
 })
+
+it('lerp', () => {
+  expect(lerp(0, 2, 0)).toEqual(0)
+  expect(lerp(0, 2, 1)).toEqual(2)
+  expect(lerp(0, 2, 0.5)).toEqual(1)
+
+  expect(lerp(-10, 10, 0.5)).toEqual(0)
+  expect(lerp(10, -10, 0.5)).toEqual(0)
+
+  expect(lerp(0, 1, -1.5)).toEqual(0)
+  expect(lerp(0, 1, 2.5)).toEqual(1)
+})
+
+it('remap', () => {
+  expect(remap(0, 0, 1, 0, 10)).toEqual(0)
+  expect(remap(1, 0, 1, 0, 10)).toEqual(10)
+  expect(remap(0.5, 0, 1, 0, 10)).toEqual(5)
+
+  expect(remap(0.5, -1, 1, 0, 1)).toEqual(0.75)
+  expect(remap(0.25, 0, 1, -1, 1)).toEqual(-0.5)
+
+  expect(remap(2, 0, 1, 5, 10)).toEqual(10)
+  expect(remap(-1, 0, 1, 5, 10)).toEqual(5)
+})

src/math.ts

@@ -7,3 +7,32 @@ export function clamp(n: number, min: number, max: number) {
 export function sum(...args: number[] | number[][]) {
   return flattenArrayable(args).reduce((a, b) => a + b, 0)
 }
+
+/**
+ * Linearly interpolates between `min` and `max` based on `t`
+ *
+ * @category Math
+ * @param t The interpolation value clamped between 0 and 1
+ * @example
+ * ```
+ * const value = lerp(0, 2, 0.5) // value will be 1
+ * ```
+ */
+export function lerp(min: number, max: number, t: number) {
+  const interpolation = clamp(t, 0.0, 1.0)
+  return min + (max - min) * interpolation
+}
+
+/**
+ * Linearly remaps a clamped value from its source range [`inMin`, `inMax`] to the destination range [`outMin`, `outMax`]
+ *
+ * @category Math
+ * @example
+ * ```
+ * const value = remap(0.5, 0, 1, 200, 400) // value will be 300
+ * ```
+ */
+export function remap(n: number, inMin: number, inMax: number, outMin: number, outMax: number) {
+  const interpolation = (n - inMin) / (inMax - inMin)
+  return lerp(outMin, outMax, interpolation)
+}