// The Nature of Code
// Daniel Shiffman
// http://natureofcode.com

// Bob class, just like our regular Mover (position, velocity, acceleration, mass)

class Bob { 
 PVector position;
 PVector velocity;
 PVector acceleration;
 float mass = 24;
 
 // Arbitrary damping to simulate friction / drag 
 float damping = 0.98;

 // For mouse interaction
 PVector dragOffset;
 boolean dragging = false;

 // Constructor
 Bob(float x, float y) {
 position = new PVector(x,y);
 velocity = new PVector();
 acceleration = new PVector();
 dragOffset = new PVector();
 } 

 // Standard Euler integration
 void update() { 
 velocity.add(acceleration);
 velocity.mult(damping);
 position.add(velocity);
 acceleration.mult(0);
 }

 // Newton's law: F = M * A
 void applyForce(PVector force) {
 PVector f = force.get();
 f.div(mass);
 acceleration.add(f);
 }


 // Draw the bob
 void display() { 
 stroke(0);
 strokeWeight(2);
 fill(175);
 if (dragging) {
 fill(50);
 }
 ellipse(position.x,position.y,mass*2,mass*2);
 } 

 // The methods below are for mouse interaction

 // This checks to see if we clicked on the mover
 void clicked(int mx, int my) {
 float d = dist(mx,my,position.x,position.y);
 if (d < mass) {
 dragging = true;
 dragOffset.x = position.x-mx;
 dragOffset.y = position.y-my;
 }
 }

 void stopDragging() {
 dragging = false;
 }

 void drag(int mx, int my) {
 if (dragging) {
 position.x = mx + dragOffset.x;
 position.y = my + dragOffset.y;
 }
 }
}