Line segments can be different lengths for each step, so the actual length of the drawn or skipped segments will be variable depending on the size of line segments for each included step. Draw Mode Java normally does all drawing in a single thread. This has the unfortunate disadvantage that it ignores button presses while drawing is taking place. For example, it ignores the Stop button. The Draw Mode choice allow you to specify whether or not to use Synchronous drawing.
Direct mode draws directly to the drawing area.
This has the advantage of allowing you to see the drawing as it proceeds, a step at a time. If you turn on animation, you should use this mode. Backing mode draws to an off-screen image, then transfers it to the drawing area when it is done. This has the advantage that your image will be instantly refreshed if you cover and then re-expose the drawing area in the main window. The chain parameter specifies the location of a parameter file to draw along with the current set of parameters.