gravity/simulator.js

import {
  EVENT_ZOOM,
  FRAMERATE_SAMPLE_DURATION,
  SCALE_POWER_MAX,
  SCALE_POWER_MIN,
} from './config.js';
import { Display } from './display.js';
import { System } from './system.js';
import { Options } from './options.js';
import { simOptions } from './sim-options.js';
import { initializeTools } from './sim-tools.js';

export class Sim {
  info = {};
  rawTime = undefined;
  time = undefined;
  timeScale = undefined;
  nextZoom = undefined;
  playing = true;
  recentFrames = [];
  frameRate = 0;

  system = undefined;
  display = undefined;
  overlay = undefined;
  pointer = undefined;
  panning = undefined;
  toolbarGroups = {};
  toolbars = {};

  isCurrentMode = () => undefined;
  getCurrentMode = () => undefined;
  setCurrentMode = () => undefined;
  getOption = () => undefined;
  setOption = () => undefined;
  onModeEnter = () => undefined;
  onModeLeave = () => undefined;

  markFrame(t) {
    const { recentFrames: rfs } = this;
    rfs.push(t);
    if (rfs.length < 2) return;
    const oldest = rfs[0];
    const newest = rfs[rfs.length - 1];
    const count = rfs.length;
    const duration = (newest - oldest);
    this.frameRate = 1000 * count / duration; // Converting from ms to s
    if (duration >= FRAMERATE_SAMPLE_DURATION) {
      rfs.shift();
    }
  }

  constructor(divId) {
    this.divId = divId;
    const div = document.getElementById(this.divId);
    this.div = div;

    this.options = new Options(this, simOptions);
    this.display = new Display(this);
    this.system = new System(this);

    initializeTools(this);

    // Initiate main loop
    this.rawTime = document.timeline.currentTime;
    this.time = 0;
    requestAnimationFrame(t => this.loop(t));
  }

  // It's better not to change the scale in the middle of possible frame calculations,
  // so use this to schedule it and let the event loop pick it up.
  // velocity should be in Sim coordinate scale
  scheduleZoom({x, y}, factor, velocity) {
    this.nextZoom = {x, y, factor, velocity};
  }

  // x, y should be in Sim coordinates
  // velocity should be in Sim coordinate scale
  zoom({x, y, factor, velocity}) {
    // x, y are the mouse coordinates, which should be the center of the new view frame
    // the new view origin should be x, y minus half the new view width and height
    // compute new scale
    this.display.scalePower += factor;
    // TODO: Lossy rescaling to expand zoom range
    if (this.display.scalePower > SCALE_POWER_MAX) this.display.scalePower = SCALE_POWER_MAX;
    if (this.display.scalePower < SCALE_POWER_MIN) this.display.scalePower = SCALE_POWER_MIN;
    // compute coordinates of new view frame
    this.display.viewOrigin.x = x - this.display.width / 2;
    this.display.viewOrigin.y = y - this.display.height / 2;

    this.pointer.clearPointerHistory();

    if (this.playing && velocity) {
      this.panning = {
        velocity: { ...velocity }
      };
    }

    const e = new CustomEvent(EVENT_ZOOM);
    this.div.dispatchEvent(e);
  }

  // Transform display coordinates to simulator coordinates using scale and viewOrigin
  screenToSim(x, y) {
    return this.display.screenToSim(x, y);
  }

  play() {
    this.playing = true;
  }

  pause() {
    this.playing = false;
  }

  getScaleDisplay() {
    const scale = 2 ** Math.abs(this.display.scalePower);
    return this.display.scalePower >= 0 ? `${scale}` : `1/${scale}`;
  }

  // cb: () => undefined
  onZoom(cb) {
    this.div.addEventListener(EVENT_ZOOM, () => {
      cb();
    });
  }

  // Main loop
  loop(currentTime) {
    this.markFrame(currentTime);
    this.timeScale = this.getOption('param.timeScale');

    const elapsedTime = (currentTime - this.rawTime) * this.timeScale;
    this.rawTime = currentTime;

    if (this.playing) {
      this.time += elapsedTime;
    }

    if (this.getOption('debug.currentMode')) {
      this.info['Mode'] = this.getCurrentMode();
    }

    if (this.getOption('debug.frameRate')) {
      this.info['Frame Rate'] = this.frameRate?.toPrecision(3);
    }

    if (this.nextZoom) {
      this.zoom(this.nextZoom);
      this.nextZoom = undefined;
    }

    if (this.getOption('debug.panningInfo')) {
      const {x, y} = this.panning?.velocity ?? {};
      this.info['Panning Velocity'] = [`${x?.toPrecision(6)}, `, y?.toPrecision(6)];
      const { centerOfMass } = this.system.computeSystemCenter();
      this.info['Center of Mass'] = [`${centerOfMass.x.toPrecision(6)}, `, centerOfMass.y.toPrecision(6)];
      this.info['Net Angular Momentum'] = this.system.computeSystemAngularMomentum().toPrecision(6);
    }

    this.display.frame(elapsedTime);
    this.system.frame(elapsedTime);
    this.overlay.frame();
    for (const group in this.toolbarGroups) {
      this.toolbarGroups[group].frame();
    }

    requestAnimationFrame(t => this.loop(t));
  }
}