Well, the law provides for a number of balancing tests to ensure that a court will respect the rights of all parties. A rule of thumb is unlikely to be specific

Well, the law provides for a number of balancing tests to ensure that a court will respect the rights of all parties. A rule of thumb is unlikely to be specific and precise enough for any practical use. For specific details, consult an attorney. Since it only applies to "public accommodations", it's highly unlikely that a drawing program will be covered, unless it's tied to a good, such as if you can have the drawing printed up for you.