Terrible depth-of-field effect for Processing.

dof.pde

void setup()
{
  size (500, 500);
  colorMode (RGB, 1);
  frameRate (25);
}

final int LAYERS = 5;
final int LOOP_LENGTH = 100;

void draw()
{
  background (1);
  
  final int FRAME = frameCount % LOOP_LENGTH;
  final float TIME = FRAME / float(LOOP_LENGTH);
  
  final float FOCUS = (cos (TIME * TWO_PI) * 0.5 + 0.5) * (LAYERS - 1);
 
  PGraphics pg = createGraphics (width, height);
  final float RECT_INC = pg.width / (2.0 * (LAYERS + 2));
  
  for (int i = 0; i != LAYERS; ++i)
  {
    pg.beginDraw();
    
    pg.colorMode (RGB, 1);
    pg.noFill();
    pg.stroke(0);
    
    pg.rect
    ( (i + 1) * RECT_INC
    , (i + 1) * RECT_INC
    , pg.width - (i + 1) * RECT_INC * 2
    , pg.height - (i + 1) * RECT_INC * 2
    );
    
    pg.filter (BLUR, abs (i - FOCUS));
    pg.endDraw();
    
    image (pg, 0, 0);
  }
  
  saveFrame ("###-blur.png");
}