/*
A Particle Class based on:
 
 "Particle animation and rendering using data parallel computation", Karl Sims 
 
 Morgen Fleisig
 21 February 2011
 */

class Particle {

  /*
head
   tail
   position
   radius
   color 
   opacity
   */

  PVector pH; //head location
  PVector pT; //tail location

  float rH = 7; //head radius--HARD-CODED TEMP--REALLY DIAMETER!
  float rT = rH*0.8; //tail radius--HARD-CODED TEMP--REALLY DIAMETER!
  float aH = 150; //head opacity--HARD-CODED TEMP
  float aT = aH*0.6; //tail opacity--HARD-CODED TEMP
  float mass = 1; //color--HARD-CODED TEMP
  //VARY THESE VALUES WITH OTHER FACTORS?

  //Not sure yet whether these should be independent for head and tail:
  PVector velocity;
  PVector acceleration;

  Particle() { //CTOR 
    pH = new PVector(70,70);
    pT = new PVector(pH.x,pH.y); //RELATE TO pH, or better: velocity
    //or shutterspeed? ie, if shutterspeed>frameRate, show blur

    velocity = new PVector(0,0);
    acceleration = new PVector(0,0);
  }

  void applyForce(PVector force) {
    mass = mass+((1/abs(pH.x-width/2))+(1/abs(pH.y-height/2)));
    //increase mass toward center of screen
    PVector f = PVector.div(force,mass);
    acceleration.add(f);
  }

  void update() {
    velocity.add(acceleration);
    pH.add(velocity);
    acceleration.mult(0);
  }

  void display() {
    //HEAD
    fill(255,aH); //color--HARD-CODED TEMP
    noStroke();
    ellipse(pH.x,pH.y,rH,rH);

    //TAIL
    //fill(255,0,0,aT); //RED--HARD-CODED TEMP
    fill(255,150,0,aT); //YELLOW--HARD-CODED TEMP
    //fill(255,aT); //WHITE--HARD-CODED TEMP [MATCHES HEAD]
    //VARY COLOR WITH OTHER FACTORS?

    pushMatrix();
    // Translate to location to render particle
    translate(pH.x,pH.y);
    //stroke(0);
    // Call vector heading function to get direction (note that pointing up is a heading of 0) and rotate
    rotate(velocity.heading2D());
    // Calculate length of vector & scale it to be bigger or smaller if necessary
    float scalar = 3;//--HARD-CODED TEMP & CHANGE VARIABLE NAME
    float body = velocity.mag()*scalar; 
    float bodyConstraint = constrain(body,0,rH+1);
    ellipse(-bodyConstraint,0,rT,rT); //Draw the "tail" portion of the particle
    popMatrix();

    checkEdges();

    //KEYPRESS BOOL to see velocity vector
    if (keyPressed == true) {
      drawVector(velocity,pH,10);
    }
  }


  void checkEdges() {
    if (pH.x > width + rH) { //width + particle radius (IMPLEMENTED AS DIAMETER)
      pH.x = 0 - rH;
    }
    if (pH.x < 0 - rH) {
      pH.x = width + rH;
    }
    if (pH.y > height + rH) {
      pH.y = 0 - rH;
    }
    if (pH.y < 0 - rH) {
      pH.y = height + rH;
    }
  }


  // From Dan Shiffman's "Simple Motion with PVector"
  // Renders a vector object 'v' as an arrow and a location 'loc'
  void drawVector(PVector v, PVector loc, float scayl) {
    pushMatrix();
    float arrowsize = 4;
    // Translate to location to render vector
    translate(loc.x,loc.y);
    stroke(255);
    // Call vector heading function to get direction (note that pointing up is a heading of 0) and rotate
    rotate(v.heading2D());
    // Calculate length of vector & scale it to be bigger or smaller if necessary
    float len = v.mag()*scayl;
    // Draw three lines to make an arrow (draw pointing up since we've rotate to the proper direction)
    line(0,0,len,0);
    line(len,0,len-arrowsize,+arrowsize/2);
    line(len,0,len-arrowsize,-arrowsize/2);
    popMatrix();
  }

//Eliminate particles at center of screen:
  boolean isDead() {
    if ((abs(pH.x - width/2) < 5) && (abs(pH.y - height/2) < 5)) {
    return true;
  } else {
  return false;
  }
 }
}