There are too many file. I do not know which one to look for.
You can use trace GUI element to add one point at a time for each time step.
However, you can use polygon GUI elements to draw pre-defined number of connected points.
You just need to define x,y as array with n elements in EJS variable page.
then assign (x[i],y[i]) with a for loop in EJS "fixed relation" page.
Add ploygin GUI element under drawingPanel2D, assign x,y as "x/y data" proper,
and EJS will show the polygons when you run it.
The following code is added at initialize page
And the following code is added at fixed relation page