final int DIAM = 200;
final int BALL_DIAMETER = 15;

int centerX, centerY;


int ballX, ballY;
int ballSpeedX = 3, ballSpeedY = 2;

void setup() {
  size( 500, 500 );
  ballX = 20;
  ballY = 30;

 centerX = width/2;
 centerY = height/2;

}

void draw() {
  background( 128 );
fill(#ff5954);
ellipse(centerX,centerY,DIAM,DIAM);

fill(255);

  ellipse( ballX, ballY, BALL_DIAMETER, BALL_DIAMETER );
  moveBall();
}



void moveBall() {
  changeSpeed();
  ballX = ballX + ballSpeedX;
  ballY = ballY + ballSpeedY;
}


void changeSpeed() {
  if ( ballX < BALL_DIAMETER/2 || ballX > width-BALL_DIAMETER/2 ) {

    ballSpeedX = -ballSpeedX;
  }
  if ( ballY < BALL_DIAMETER/2 || ballY > height-BALL_DIAMETER/2 ) {

    ballSpeedY = -ballSpeedY;
  }

   if(dist(ballX,ballY,centerX,centerY) < (DIAM/2) + (BALL_DIAMETER/2)){

   ballSpeedX = -ballSpeedX;
   ballSpeedY = -ballSpeedY;
   }

}