@matematrolii/sketchbook/src/ts/physics/spring_simulation/SpringSimulator.ts

3D matematrolii playground built on three.js and cannon.js

import * as THREE from 'three';
import { SimulatorBase } from './SimulatorBase';
import { SimulationFrame } from './SimulationFrame';
import { spring } from '../../core/FunctionLibrary';

export class SpringSimulator extends SimulatorBase
{
	public position: number;
	public velocity: number;
	public target: number;
	public cache: SimulationFrame[];
	
	constructor(fps: number, mass: number, damping: number, startPosition: number = 0, startVelocity: number = 0)
	{
		// Construct base
		super(fps, mass, damping);

		// Simulated values
		this.position = startPosition;
		this.velocity = startVelocity;

		// Simulation parameters
		this.target = 0;

		// Initialize cache by pushing two frames
		this.cache = []; // At least two frames
		for (let i = 0; i < 2; i++)
		{
			this.cache.push(
				new SimulationFrame(startPosition, startVelocity),
			);
		}
	}

	/**
	 * Advances the simulation by given time step
	 * @param {number} timeStep 
	 */
	public simulate(timeStep: number): void
	{
		// Generate new frames
		this.generateFrames(timeStep);

		// Return values interpolated between cached frames
		this.position = THREE.MathUtils.lerp(this.cache[0].position, this.cache[1].position, this.offset / this.frameTime);
		this.velocity = THREE.MathUtils.lerp(this.cache[0].velocity, this.cache[1].velocity, this.offset / this.frameTime);
	}

	/**
	 * Gets another simulation frame
	 */
	public getFrame(isLastFrame: boolean): SimulationFrame
	{
		return spring(this.lastFrame().position, this.target, this.lastFrame().velocity, this.mass, this.damping);
	}
}