added various interpolation related functions

src/mol-math/interpolate.ts

+/**
+ * Copyright (c) 2018 mol* contributors, licensed under MIT, See LICENSE file for more info.
+ *
+ * @author Alexander Rose <alexander.rose@weirdbyte.de>
+ */
+
+export function normalize (value: number, min: number, max: number) {
+    return (value - min) / (max - min)
+}
+
+export function clamp (value: number, min: number, max: number) {
+    return Math.max(min, Math.min(max, value))
+}
+
+export function pclamp (value: number) {
+    return clamp(value, 0, 100)
+}
+
+export function saturate (value: number) {
+    return clamp(value, 0, 1)
+}
+
+export function damp (value: number, dampingFactor: number) {
+    const dampedValue = value * dampingFactor
+    return Math.abs(dampedValue) < 0.1 ? 0 : dampedValue
+}
+
+export function lerp (start: number, stop: number, alpha: number) {
+    return start + (stop - start) * alpha
+}
+
+export function spline (p0: number, p1: number, p2: number, p3: number, t: number, tension: number) {
+    const v0 = (p2 - p0) * tension
+    const v1 = (p3 - p1) * tension
+    const t2 = t * t
+    const t3 = t * t2
+    return (2 * p1 - 2 * p2 + v0 + v1) * t3 + (-3 * p1 + 3 * p2 - 2 * v0 - v1) * t2 + v0 * t + p1
+}
+
+export function smoothstep (min: number, max: number, x: number) {
+    x = saturate(normalize(x, min, max))
+    return x * x * (3 - 2 * x)
+}
+
+export function smootherstep (min: number, max: number, x: number) {
+    x = saturate(normalize(x, min, max))
+    return x * x * x * (x * (x * 6 - 15) + 10)
+}
+
+export function smootheststep (min: number, max: number, x: number) {
+    x = saturate(normalize(x, min, max))
+    return -20 * Math.pow(x, 7) + 70 * Math.pow(x, 6) - 84 * Math.pow(x, 5) + 35 * Math.pow(x, 4)
+}
+
+export function almostIdentity (value: number, start: number, stop: number) {
+    if (value > start) return value
+    const a = 2 * stop - start
+    const b = 2 * start - 3 * stop
+    const t = value / start
+    return (a * t + b) * t * t + stop
+}
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