/** Creates a rectangle and adds it to the DisplayFrame. */
public void calculate() {
// gets rectangle location
double left = control.getDouble("xleft");
double top = control.getDouble("ytop");
// gets rectangle dimensions
double width = control.getDouble("width");
double height = control.getDouble("height");
Drawable rectangle = new WorldRectangle(left, top, width, height);
frame.addDrawable(rectangle);
// frame is automatically rendered after Calculate button is pressed
}
