Cat theOneCat;

void setup() {
  size(800, 600);

  theOneCat = new Cat();
  theOneCat.posX = width/2;
  theOneCat.posY = height/2;
}


void draw() {
  background(255);

  noStroke();
  fill(255, 0, 255);
  ellipse(mouseX, mouseY, 100, 100);

  theOneCat.chase(mouseX, mouseY);

  theOneCat.drawCat();
}


class Cat {
  float posX;
  float posY;
  float speed = 1.5;

  void drawCat() {
    noStroke();
    fill(0);
    ellipse(this.posX, this.posY, 100, 100);
  }

  void chase(int targetX, int targetY) {
    //println("Cat: I'm moving to " + targetX + " " + targetY);

    float diffX = targetX - this.posX;
    float diffY = targetY - this.posY;

    float angle = atan2(diffY, diffX);

    println("angle (rad) " + angle + " (deg) " + degrees(angle));

    float moveX = cos(angle) * this.speed;
    float moveY = sin(angle) * this.speed;

    this.posX += moveX;
    this.posY += moveY;


    // as alternative, you could use this too
    // it's simpler to write, but less simple to control the speed
    /*
    this.posX += diffX * 0.1;
    this.posY += diffY * 0.1;
    */

  }
}