PVector location;
PVector velocity;

void setup() {
	size(200,200);
	smooth();
	background(255);
	location = new PVector(100,100);
	velocity = new PVector(2.5,5);
}

void draw() {
	noStroke();
	fill(255,10);
	rect(0,0,width,height);
	location.add(velocity);
	if ((location.x > width) || (location.x < 0)) 
		{
			velocity.x = velocity.x * -1;
		}
	if ((location.y > height) || (location.y < 0)) 
		{
			velocity.y = velocity.y * -1;
		}
	stroke(0);
	fill(175);
	ellipse(location.x,location.y,16,16);
}