sketch.js

function setup() {
  createCanvas(640, 480);

  // use anti-aliasing
  smooth();

  // no stroke on my shapes
  noStroke();

  /*
    use upper left corner
    not the center
  */
  ellipseMode( CORNER );

  // just run the draw cycle 1 time :)
  //noLoop();
}

function draw() {
  background( 0, 255, 0 );
  rect( 10, 10, 10, 10 );
}