preloadCallback = function (resp) {
      context._setProperty('_preloadCount', context._preloadCount - 1);
      if (context._preloadCount === 0) {
        var loadingScreen = document.getElementById(context._loadingScreenId);
        if (loadingScreen) {
          loadingScreen.parentNode.removeChild(loadingScreen);
        }
        context._setup();
        context._runFrames();
        context._draw();
      }
    }
Called directly after setup(), the draw() function continuously executes
the lines of code contained inside its block until the program is stopped
or noLoop() is called. draw() is called automatically and should never be
called explicitly.

It should always be controlled with noLoop(), redraw() and loop(). After
noLoop() stops the code in draw() from executing, redraw() causes the
code inside draw() to execute once, and loop() will cause the code
inside draw() to resume executing continuously.

The number of times draw() executes in each second may be controlled with
the frameRate() function.

There can only be one draw() function for each sketch, and draw() must
exist if you want the code to run continuously, or to process events such
as mousePressed(). Sometimes, you might have an empty call to draw() in
your program, as shown in the above example.

@method draw
@example
<div><code>
var yPos = 0;
function setup() {  // setup() runs once
  frameRate(30);
}
function draw() {  // draw() loops forever, until stopped
  background(204);
  yPos = yPos - 1;
  if (yPos < 0) {
    yPos = height;
  }
  line(0, yPos, width, yPos);
}
</code></div>