64 lines
1.4 KiB
TypeScript
64 lines
1.4 KiB
TypeScript
const epsilon = 0.01;
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export const clamp = (a: number, b: number) => (x: number) =>
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Math.max(a, Math.min(b, x));
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/**
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* step the spring, mutate the state to reflect the state at t+dt
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*
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*/
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const stepSpringOne = (
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s: { x: number; v: number },
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{
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tension,
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friction,
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maxVelocity = Infinity,
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}: { tension: number; friction: number; maxVelocity?: number },
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target: number,
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dt = 1 / 60,
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) => {
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const a = -tension * (s.x - target) - friction * s.v;
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s.v += a * dt;
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s.v = clamp(-maxVelocity / dt, maxVelocity / dt)(s.v);
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s.x += s.v * dt;
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};
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/**
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* return true if the spring is to be considered in a stable state
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* ( close enough to the target and with a small enough velocity )
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*/
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export const isStable = (
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s: { x: number; v: number },
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target: number,
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dt = 1 / 60,
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) => Math.abs(s.x - target) < epsilon && Math.abs(s.v * dt) < epsilon;
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export const isStableAndBound = (
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s: { x: number; v: number },
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target: number,
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dt?: number,
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) => {
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const stable = isStable(s, target, dt);
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if (stable) {
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s.x = target;
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s.v = 0;
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}
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return stable;
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};
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export const stepSpring = (
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s: { x: number; v: number },
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params: { tension: number; friction: number; maxVelocity?: number },
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target: number,
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dt = 1 / 60,
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) => {
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const interval = 1 / 60;
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while (dt > 0) {
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stepSpringOne(s, params, target, Math.min(interval, dt));
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// eslint-disable-next-line no-param-reassign
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dt -= interval;
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}
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};
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