Adding Activity to the Object Reactor Callback Functions (AutoLISP)

In Lesson 6, you registered two callback functions with object reactor events. The gp:outline-erased function was associated with the:vlr-erased reactor event, and gp:outline-changed was associated with the :vlr-modified event. You need to make these functions do what they are intended to do.

To make the object reactor callback functions do what they are intended to do

1. In gpreact.lsp, change gp:outline-erased so it appears as follows:

   (defun gp:outline-erased (outlinePoly reactor parameterList)
     (setq *reactorsToRemove*
          (cons reactor *reactorsToRemove*))
     (princ)
   ) ;_ end of defun

   There is just one operation performed here. The reactor attached to the polyline is saved to a list of all reactors that need to be removed. (Remember: though reactors are attached to entities, they are separate objects entirely, and their relationships to entities need to be managed just as carefully as regular AutoCAD entities.)

2. Change gp:outline-changed to reflect the following code:

   (defun gp:outline-changed (outlinePoly reactor parameterList)
     (if *lostAssociativity*
       (setq *reactorsToRemove*
                                (cons reactor *reactorsToRemove*))
       (setq *polytochange*     outlinePoly
             *reactorsToChange* (cons reactor *reactorsToChange*))
       )
     (princ)
   )

   There are two categories of functions that can modify the polyline outline. The first category contains those commands that will break the path's associativity with its tiles. You checked for this condition in gp:command-will-start and set the *lostAssociativity* global variable accordingly. In this case, the tiles need to be erased, and the path is then in the user's hands. The other category is the grip mode of the STRETCH command, where associativity is retained and you need to straighten out the outline after the user has finished dragging a vertex to a new location.

   The *polyToChange* variable stores a VLA-Object pointer to the polyline itself. This will be used in the gp:command-ended function when it comes time to recalculate the polyline border.