Source Code:            Syntax: C#

// Constrain
// by REAS <http://reas.com>

// Move the mouse across the screen to move the circle.
// The program constrains the circle to its box.

// Updated 20 January 2003

double mx;
double my;
double delay = 40.0;
double eiSize = 25.0;
int box = 30;

public override void setup() 
{
  size(200, 200);
  noStroke(); 
  smooth();
  ellipseMode(CENTER_RADIUS);  
}

public override void draw() 
{ 
  background(51);
  
  if(abs(mouseX - mx) > 0.1) {
    mx = mx + (mouseX - mx)/delay;
  }
  if(abs(mouseY - my) > 0.1) {
    my = my + (mouseY- my)/delay;
  }
  
  double distance = eiSize * 2;
  mx = constrain(mx, box+distance, width-box-distance);
  my = constrain(my, box+distance, height-box-distance);
  fill(76);
  rect(box+eiSize, box+eiSize, box*3, box*3);
  fill(255);  
  ellipse(mx, my, eiSize, eiSize);
}