let lifeSpanMin = 50;

let lifeSpanMax = 100;

let maxVel = 3;

let repChance = 0.01;

let viewButton;

let toggleViewGate = true;

​

function createParticles(posX,posY){

  for(let i = random(1,5); i >= 0; i--){

    particles.push(new Particle(posX,posY));

  }

}

​

function mouseDragged(){

  createParticles(mouseX,mouseY);

}

​

function setup() {

  createCanvas(windowWidth, windowHeight);

  viewButton = createButton('Toggle View');

  viewButton.position(10, height+20);

  viewButton.mousePressed(function toggle(){toggleViewGate = !toggleViewGate;});

}

​

function draw() {

  background(220);

  for(let i = particles.length - 1; i >= 0; i--){

    let p = particles[i];

    if(p.alive){

      p.repoduce();

      p.update();

      p.findNeighbors(particles);

      p.show();

    }else{

      particles.splice(i,1);

    }

  }

}

​

class Particle{

  constructor(posX,posY){

    this.pos = createVector(posX,posY);

    this.vel = createVector(random(-maxVel,maxVel),random(-maxVel,maxVel));

    this.acc = createVector();

    this.lifeMax = random(lifeSpanMin,lifeSpanMax);

    this.lifeSpan = 0;

    this.alive = true; 

    this.neighbors = []; 

    this.hue = createVector(0,0,0);

  }

  repoduce(){

    if(random(1) < repChance && this.lifeSpan > this.lifeMax/2){

      createParticles(this.pos.x,this.pos.y);

    }

  }

  findNeighbors(particles){

    this.neighbors = []; 

    let range = map  (this.lifeMax,lifeSpanMin,lifeSpanMax,10,50);

    for(let p of particles){

      if(p != this && !p.neighbors.includes(this)){

        let d = this.pos.dist(p.pos);

        if(d < range){

          this.neighbors.push(p);

        }

      }

    }

  }

  update(){

    if(this.lifeSpan <= this.lifeMax){

      this.lifeSpan ++;

    }else{

      this.alive = false; 

    }

    //this.vel.add(this.acc);

    this.vel.mult(0.95);

    this.pos.add(this.vel);

    //this.acc.mult(0);

  }

  show(){

    this.hue.x = map(this.lifeSpan, 0, this.lifeMax, 21,35);

    this.hue.y = map(this.lifeSpan, 0, this.lifeMax,  34, 57);

    this.hue.z = map(this.lifeSpan, 0, this.lifeMax,  56, 93);

    let alpha = map(this.lifeSpan, 0, this.lifeMax, 50, 1);

    stroke(this.hue.x,this.hue.y,this.hue.z,alpha);

    point(this.pos.x,this.pos.y);

    if(toggleViewGate){

      noFill();

      for(let n of this.neighbors){

        line(this.pos.x,this.pos.y,n.pos.x,n.pos.y);

      }

    }else{

      noStroke();

      fill(this.hue.x,this.hue.y,this.hue.z,alpha);

      beginShape();

      vertex(this.pos.x,this.pos.y);

      for(let n of this.neighbors){

        vertex(n.pos.x,n.pos.y);

      }

      vertex(this.pos.x,this.pos.y);

      endShape();

    }

  }

}