Week 5 Particles with tails

Particles_Lesson_5
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ArrayList particles = new ArrayList();
​
void setup() {
  size(640,640);
  for (int i =0; i<20; i++) {
    particles.add(new Particle(new PVector(random(width), random(height)))); // initialize the location for the main particle system in an array
  }
}
​
void draw() {
  background(20);
  for (int i =0; i<particles.size(); i++) { // Make each particle in the array follow the functionality in its class.
    Particle p = (Particle) particles.get(i);
    p.motion();
    p.constraints();
  }
}
​
class Particle {
  int tailLength = 50;
  int tailStep = 5;
  
  
  PVector [] tailPositions = new PVector [tailLength];
  PVector location;
  PVector velocity;
  PVector acceleration;
  
  
  Particle(PVector location_) {
    location = location_;
    velocity = new PVector((1-random(2)), 1-random(2));
    velocity.mult(4);
    acceleration = new PVector();
    for (int i = 0; i < tailLength; i++) {
      tailPositions[i] = new PVector(i,i);
    }
  }
  
  void motion() {
    PVector mouse = new PVector(mouseX, mouseY);
    if (mousePressed) { // Establishes boolean for acceleration directed towards the mouse if mouse is pressed and makes particles move towards cursor
    PVector dir = PVector.sub(mouse,location);
    dir.normalize();
    dir.mult(.5);
    acceleration = dir;
    }
    velocity.add(acceleration);
    location.add(velocity);
   acceleration.mult(0); // By bringing acceleration back to 0 after any mouse press occurs, we avoid having particles potentially leave the window
    
    drawParticlesTails(0, location);
    for (int i = 0; i < tailPositions.length-1; i++) {
      drawParticlesTails(i+1, tailPositions[i]);
    }
  }
  
  void drawParticlesTails(int i, PVector location_c) {
    float direction = atan2(location_c.y - tailPositions[i].y, location_c.x - tailPositions[i].x);
    tailPositions[i].x = location_c.x - cos(direction) * tailStep;
    tailPositions[i].y = location_c.y - sin(direction) * tailStep;
    
    pushMatrix();
    translate(tailPositions[i].x, tailPositions[i].y); // Our tail begin at x,y = (0,0) so we reorient the coordinate system so that (0,0) is at the center of the window.
    rotate(direction);
    noStroke();
    fill(125 + sin(radians(frameCount))*125, 125 + cos(radians(frameCount))*125, 125 + sin(radians(-frameCount))*125);
    float r = map(i,0,tailLength, 30, 1);
    ellipse(location_c.x, location_c.y, r, r);
    popMatrix();
  }
  
  void constraints() {
    if ((location.x>width) || (location.x <0)) {
      velocity.x = velocity.x * -1;
    }
    
    if ((location.y>height) || (location.y <0)) {
      velocity.y = velocity.y * -1;
  }
}
}
​
​