void setup()
{
  size(300, 300);
  fill(234);
  background(0);
  frameRate(25);
  smooth();
}

int xer = 150;
int yer = 150;
float xmove = 1;
float ymove = 1;
int xcenterpull=0;
int ycenterpull=0;
int move = 10;

void draw()
{
  fill(0, 20);
  rect (0,0,300,300);
  fill(255);
  if (xer <0)
  {
    xcenterpull=20;
  }
  if (xer > width)
  {
    xcenterpull=move*-2;
  }
  if (xer < width && xer > 0)
  {
    xcenterpull=move*-1;
  }
  if (yer <0)
  {
    ycenterpull=20;
  }
  if (yer > width)
  {
    ycenterpull=move*-2;
  }
  if (yer < width && yer > 0)
  {
    ycenterpull=move*-1;
  }
  xmove = (random(move*2)+xcenterpull);
  ymove = (random(move*2)+ycenterpull);
  xer += xmove;
  yer += ymove;
   // background(0);
    ellipse(xer, yer, 10, 10);

}