processing4/java/examples/Topics/Vectors/AccelerationWithVectors/Mover.pde

/**
 * Acceleration with Vectors 
 * by Daniel Shiffman.  
 * 
 * Demonstration of the basics of motion with vector.
 * A "Mover" object stores location, velocity, and acceleration as vectors
 * The motion is controlled by affecting the acceleration (in this case towards the mouse)
 */


class Mover {

  // The Mover tracks location, velocity, and acceleration 
  PVector location;
  PVector velocity;
  PVector acceleration;
  // The Mover's maximum speed
  float topspeed;

  Mover() {
    // Start in the center
    location = new PVector(width/2,height/2);
    velocity = new PVector(0,0);
    topspeed = 5;
  }

  void update() {
    
    // Compute a vector that points from location to mouse
    PVector mouse = new PVector(mouseX,mouseY);
    PVector acceleration = PVector.sub(mouse,location);
    // Set magnitude of acceleration
    acceleration.setMag(0.2);
    
    // Velocity changes according to acceleration
    velocity.add(acceleration);
    // Limit the velocity by topspeed
    velocity.limit(topspeed);
    // Location changes by velocity
    location.add(velocity);
  }

  void display() {
    stroke(255);
    strokeWeight(2);
    fill(127);
    ellipse(location.x,location.y,48,48);
  }

}