Planning the Overall Reactor Process

You need to define several new functions in this lesson. Rather than present you with details on all aspects of the new code, this lesson presents an overview and points out the concepts behind the code. At the end of the lesson, you will have all the source code necessary to create a garden path application identical to the sample program you ran in Lesson 1.

NoteWhen you are in the midst of developing and debugging reactor-based applications, there is always the potential of leaving AutoCAD. in an unstable state. This can be caused by several situations, such as failing to remove a reactor from deleted entities. For this reason, it is recommended that before beginning Lesson 7, you should close VLISP, save any open files as you do so, exit AutoCAD, then restart both applications.

Begin by loading the project as it existed at the end of Lesson 6.

Two obvious pieces of work remain to be done in the garden path application:

You also need to consider how to handle the global variables in your program. Often, it is desirable to have globals retain a value throughout an AutoCAD drawing session. In the case of reactors, however, this is not the case. To illustrate this, imagine a user of your garden path application has drawn several garden paths in a single drawing. After doing this, the user erases them, first one at a time, then two at a time, and so on, until all but one path is erased.

Lesson 5 introduced a global variable *reactorsToRemove*, responsible for storing pointers to the reactors for the polylines about to be erased. When *reactorsToRemove* is declared in gp:outline-erased, the event lets you know the polyline is about to be erased. The polyline is not actually removed until the gp:command-ended event fires.

The first time the user deletes a polyline, things work just as you would expect. In gp:outline-erased, you store a pointer to the reactor. When gp:command-ended fires, you remove the tiles associated with the polyline to which the reactor is attached, and all is well. Then, the user decides to erase two paths. As a result, your application will get two calls to gp:outline-erased, one for each polyline about to be erased. There are two potential problems you must anticipate:

Here is the chain of events that needs to occur for users to erase two garden paths with a single erase command. Note how global variables are handled:

In addition to the *reactorsToRemove*global, your application also includes a *polyToChange* global, which stores a pointer to any polyline that will be modified. Two additional globals for the application will be introduced later in this lesson.