jrtechs-vis/lib/network/modules/PhysicsEngine.js

/**
 * Created by Alex on 2/23/2015.
 */

import {BarnesHutSolver} from "./components/physics/BarnesHutSolver";
import {Repulsion} from "./components/physics/RepulsionSolver";
import {HierarchicalRepulsion} from "./components/physics/HierarchicalRepulsionSolver";

import {SpringSolver} from "./components/physics/SpringSolver";
import {HierarchicalSpringSolver} from "./components/physics/HierarchicalSpringSolver";

import {CentralGravitySolver} from "./components/physics/CentralGravitySolver";

var util = require('../../util');


class PhysicsEngine {
  constructor(body) {
    this.body = body;
    this.physicsBody = {physicsNodeIndices:[], physicsEdgeIndices:[], forces: {}, velocities: {}};

    this.simulationInterval = 1000 / 60;
    this.requiresTimeout = true;
    this.previousStates = {};
    this.renderTimer == undefined;

    this.stabilized = false;
    this.stabilizationIterations = 0;
    this.ready = false; // will be set to true if the stabilize

    // default options
    this.options = {};
    this.defaultOptions = {
      barnesHut: {
        thetaInverted: 1 / 0.5, // inverted to save time during calculation
        gravitationalConstant: -2000,
        centralGravity: 0.3,
        springLength: 95,
        springConstant: 0.04,
        damping: 0.09
      },
      repulsion: {
        centralGravity: 0.0,
        springLength: 200,
        springConstant: 0.05,
        nodeDistance: 100,
        damping: 0.09
      },
      hierarchicalRepulsion: {
        centralGravity: 0.0,
        springLength: 100,
        springConstant: 0.01,
        nodeDistance: 150,
        damping: 0.09
      },
      model: 'BarnesHut',
      timestep: 0.5,
      maxVelocity: 50,
      minVelocity: 0.1,    // px/s
      stabilization: {
        enabled: true,
        iterations: 1000,   // maximum number of iteration to stabilize
        updateInterval: 100,
        onlyDynamicEdges: false,
        zoomExtent: true
      }
    }
    util.extend(this.options, this.defaultOptions);

    this.body.emitter.on("initPhysics",     () => {this.initPhysics();});
    this.body.emitter.on("resetPhysics",    () => {this.stopSimulation(); this.ready = false;});
    this.body.emitter.on("startSimulation", () => {
      if (this.ready === true) {
        this.stabilized = false;
        this.runSimulation();
      }
    })
    this.body.emitter.on("stopSimulation",  () => {this.stopSimulation();});
  }

  setOptions(options) {
    if (options !== undefined) {
      if (typeof options.stabilization == 'boolean') {
        options.stabilization = {
          enabled: options.stabilization
        }
      }
      util.deepExtend(this.options, options);
    }
    this.init();
  }


  init() {
    var options;
    if (this.options.model == "repulsion") {
      options = this.options.repulsion;
      this.nodesSolver = new Repulsion(this.body, this.physicsBody, options);
      this.edgesSolver = new SpringSolver(this.body, this.physicsBody, options);
    }
    else if (this.options.model == "hierarchicalRepulsion") {
      options = this.options.hierarchicalRepulsion;
      this.nodesSolver = new HierarchicalRepulsion(this.body, this.physicsBody, options);
      this.edgesSolver = new HierarchicalSpringSolver(this.body, this.physicsBody, options);
    }
    else { // barnesHut
      options = this.options.barnesHut;
      this.nodesSolver = new BarnesHutSolver(this.body, this.physicsBody, options);
      this.edgesSolver = new SpringSolver(this.body, this.physicsBody, options);
    }

    this.gravitySolver = new CentralGravitySolver(this.body, this.physicsBody, options);
    this.modelOptions = options;
  }

  initPhysics() {
    this.stabilized = false;
    this.ready = true;
    if (this.options.stabilization.enabled === true) {
      this.stabilize();
    }
    else {
      this.body.emitter.emit("zoomExtent", {duration:0}, true)
      this.runSimulation();
    }
  }

  stopSimulation() {
    this.stabilized = true;
    if (this.viewFunction !== undefined) {
      this.body.emitter.off("initRedraw", this.viewFunction);
      this.viewFunction = undefined;
      this.body.emitter.emit("_stopRendering");
    }
  }

  runSimulation() {
    if (this.viewFunction === undefined) {
      this.viewFunction = this.simulationStep.bind(this);
      this.body.emitter.on("initRedraw", this.viewFunction);
      this.body.emitter.emit("_startRendering");
    }
  }

  simulationStep() {
    // check if the physics have settled
    var startTime = Date.now();
    this.physicsTick();
    var physicsTime = Date.now() - startTime;

    // run double speed if it is a little graph
    if ((physicsTime < 0.4 * this.simulationInterval || this.runDoubleSpeed == true) && this.stabilized === false) {
      this.physicsTick();

      // this makes sure there is no jitter. The decision is taken once to run it at double speed.
      this.runDoubleSpeed = true;
    }

    if (this.stabilized === true) {
      if (this.stabilizationIterations > 1) {
        // trigger the "stabilized" event.
        // The event is triggered on the next tick, to prevent the case that
        // it is fired while initializing the Network, in which case you would not
        // be able to catch it
        var me = this;
        var params = {
          iterations: this.stabilizationIterations
        };
        this.stabilizationIterations = 0;
        this.startedStabilization = false;
        setTimeout(function () {
          me.body.emitter.emit("stabilized", params);
        }, 0);
      }
      else {
        this.stabilizationIterations = 0;
      }
      this.stopSimulation();
    }
  }

  /**
   * A single simulation step (or "tick") in the physics simulation
   *
   * @private
   */
  physicsTick() {
    if (this.stabilized === false) {
      this.calculateForces();
      this.stabilized = this.moveNodes();

      // determine if the network has stabilzied
      if (this.stabilized === true) {
        this.revert();
      }
      else {
        // this is here to ensure that there is no start event when the network is already stable.
        if (this.startedStabilization == false) {
          this.body.emitter.emit("startStabilizing");
          this.startedStabilization = true;
        }
      }

      this.stabilizationIterations++;
    }
  }

  /**
   * Smooth curves are created by adding invisible nodes in the center of the edges. These nodes are also
   * handled in the calculateForces function. We then use a quadratic curve with the center node as control.
   * This function joins the datanodes and invisible (called support) nodes into one object.
   * We do this so we do not contaminate this.body.nodes with the support nodes.
   *
   * @private
   */
  _updatePhysicsIndices() {
    this.physicsBody.forces = {};
    this.physicsBody.physicsNodeIndices = [];
    this.physicsBody.physicsEdgeIndices = [];
    let nodes = this.body.nodes;
    let edges = this.body.edges;

    // get node indices for physics
    for (let nodeId in nodes) {
      if (nodes.hasOwnProperty(nodeId)) {
        if (nodes[nodeId].options.physics === true) {
          this.physicsBody.physicsNodeIndices.push(nodeId);
        }
      }
    }

    // get edge indices for physics
    for (let edgeId in edges) {
      if (edges.hasOwnProperty(edgeId)) {
        if (edges[edgeId].options.physics === true) {
          this.physicsBody.physicsEdgeIndices.push(edgeId);
        }
      }
    }

    // get the velocity and the forces vector
    for (let i = 0; i < this.physicsBody.physicsNodeIndices.length; i++) {
      let nodeId = this.physicsBody.physicsNodeIndices[i];
      this.physicsBody.forces[nodeId] = {x:0,y:0};

      // forces can be reset because they are recalculated. Velocities have to persist.
      if (this.physicsBody.velocities[nodeId] === undefined) {
        this.physicsBody.velocities[nodeId] = {x:0,y:0};
      }
    }

    // clean deleted nodes from the velocity vector
    for (let nodeId in this.physicsBody.velocities) {
      if (nodes[nodeId] === undefined) {
        delete this.physicsBody.velocities[nodeId];
      }
    }
  }


  revert() {
    var nodeIds = Object.keys(this.previousStates);
    var nodes = this.body.nodes;
    var velocities = this.physicsBody.velocities;

    for (let i = 0; i < nodeIds.length; i++) {
      let nodeId = nodeIds[i];
      if (nodes[nodeId] !== undefined) {
        velocities[nodeId].x = this.previousStates[nodeId].vx;
        velocities[nodeId].y = this.previousStates[nodeId].vy;
        nodes[nodeId].x = this.previousStates[nodeId].x;
        nodes[nodeId].y = this.previousStates[nodeId].y;
      }
      else {
        delete this.previousStates[nodeId];
      }
    }
  }

  moveNodes() {
    var nodesPresent = false;
    var nodeIndices = this.physicsBody.physicsNodeIndices;
    var maxVelocity = this.options.maxVelocity === 0 ? 1e9 : this.options.maxVelocity;
    var stabilized = true;
    var vminCorrected = this.options.minVelocity / Math.max(this.body.view.scale,0.05);

    for (let i = 0; i < nodeIndices.length; i++) {
      let nodeId = nodeIndices[i];
      let nodeVelocity = this._performStep(nodeId, maxVelocity);
      // stabilized is true if stabilized is true and velocity is smaller than vmin --> all nodes must be stabilized
      stabilized = nodeVelocity < vminCorrected && stabilized === true;
      nodesPresent = true;
    }


    if (nodesPresent == true) {
      if (vminCorrected > 0.5*this.options.maxVelocity) {
        return false;
      }
      else {
        return stabilized;
      }
    }
    return true;
  }

  _performStep(nodeId,maxVelocity) {
    var node = this.body.nodes[nodeId];
    var timestep = this.options.timestep;
    var forces = this.physicsBody.forces;
    var velocities = this.physicsBody.velocities;

    // store the state so we can revert
    this.previousStates[nodeId] = {x:node.x, y:node.y, vx:velocities[nodeId].x, vy:velocities[nodeId].y};

    if (!node.xFixed) {
      let dx   = this.modelOptions.damping * velocities[nodeId].x;   // damping force
      let ax   = (forces[nodeId].x - dx) / node.options.mass;        // acceleration
      velocities[nodeId].x += ax * timestep;                         // velocity
      velocities[nodeId].x = (Math.abs(velocities[nodeId].x) > maxVelocity) ? ((velocities[nodeId].x > 0) ? maxVelocity : -maxVelocity) : velocities[nodeId].x;
      node.x  += velocities[nodeId].x * timestep;                    // position
    }
    else {
      forces[nodeId].x = 0;
      velocities[nodeId].x = 0;
    }

    if (!node.yFixed) {
      let dy   = this.modelOptions.damping * velocities[nodeId].y;    // damping force
      let ay   = (forces[nodeId].y - dy) / node.options.mass;         // acceleration
      velocities[nodeId].y += ay * timestep;                          // velocity
      velocities[nodeId].y = (Math.abs(velocities[nodeId].y) > maxVelocity) ? ((velocities[nodeId].y > 0) ? maxVelocity : -maxVelocity) : velocities[nodeId].y;
      node.y  += velocities[nodeId].y * timestep;                     // position
    }
    else {
      forces[nodeId].y = 0;
      velocities[nodeId].y = 0;
    }

    var totalVelocity = Math.sqrt(Math.pow(velocities[nodeId].x,2) + Math.pow(velocities[nodeId].y,2));
    return totalVelocity;
  }

  calculateForces() {
    this.gravitySolver.solve();
    this.nodesSolver.solve();
    this.edgesSolver.solve();
  }









  /**
   * When initializing and stabilizing, we can freeze nodes with a predefined position. This greatly speeds up stabilization
   * because only the supportnodes for the smoothCurves have to settle.
   *
   * @private
   */
  _freezeNodes() {
    var nodes = this.body.nodes;
    for (var id in nodes) {
      if (nodes.hasOwnProperty(id)) {
        if (nodes[id].x != null && nodes[id].y != null) {
          nodes[id].fixedData.x = nodes[id].xFixed;
          nodes[id].fixedData.y = nodes[id].yFixed;
          nodes[id].xFixed = true;
          nodes[id].yFixed = true;
        }
      }
    }
  }

  /**
   * Unfreezes the nodes that have been frozen by _freezeDefinedNodes.
   *
   * @private
   */
  _restoreFrozenNodes() {
    var nodes = this.body.nodes;
    for (var id in nodes) {
      if (nodes.hasOwnProperty(id)) {
        if (nodes[id].fixedData.x != null) {
          nodes[id].xFixed = nodes[id].fixedData.x;
          nodes[id].yFixed = nodes[id].fixedData.y;
        }
      }
    }
  }

  /**
   * Find a stable position for all nodes
   * @private
   */
  stabilize() {
    if (this.options.stabilization.onlyDynamicEdges == true) {
      this._freezeNodes();
    }
    this.stabilizationSteps = 0;
  
    setTimeout(this._stabilizationBatch.bind(this),0);
  }

  _stabilizationBatch() {
    var count = 0;
    while (this.stabilized == false && count < this.options.stabilization.updateInterval && this.stabilizationSteps < this.options.stabilization.iterations) {
      this.physicsTick();
      this.stabilizationSteps++;
      count++;
    }
  
    if (this.stabilized == false && this.stabilizationSteps < this.options.stabilization.iterations) {
      this.body.emitter.emit("stabilizationProgress", {steps: this.stabilizationSteps, total: this.options.stabilization.iterations});
      setTimeout(this._stabilizationBatch.bind(this),0);
    }
    else {
      this._finalizeStabilization();
    }
  }

  _finalizeStabilization() {
    if (this.options.stabilization.zoomExtent == true) {
      this.body.emitter.emit("zoomExtent", {duration:0});
    }

    if (this.options.stabilization.onlyDynamicEdges == true) {
      this._restoreFrozenNodes();
    }
    
    this.body.emitter.emit("stabilizationIterationsDone");
    this.body.emitter.emit("_requestRedraw");
  }
  
}

export default PhysicsEngine;