a reactor-based application, you need to handle any command that
affects your objects in a significant way. One of your program
design activities should be to review all possible AutoCAD editing
commands and determine how your application should respond to each
one. The format of the reactor-trace sheet shown near the end of
Lesson 6 is very good for this purpose. Invoke the commands you
expect your user to use, and write down the kind of behavior with
which your application should respond. Other actions to plan for
Determine what to do when users issue UNDO and REDO
Determine what to do when users issue the OOPS command after
erasing entities linked with reactors.
To prevent a
very complex subject from becoming very, very
complex, the tutorial does not try to cover all the possibilities
that should be covered, and the functionality within this lesson is
kept to an absolute minimum.
you won't be building in the complete functionality for these extra
commands, examine what a few additional editing functions would
require you to do:
If users stretch a polyline boundary (using the STRETCH
command) several things should happen. It could be stretched in any
direction, not just on the major or minor axis, so the boundary may
end up in a very odd shape. In addition, you need to take into
consideration how many vertices have been stretched. A situation
where only one vertex is stretched will result in a polyline quite
different from one in which two vertices are moved. In any case,
the tiles must be erased and new positions recalculated once you
determine the adjustments needed to the boundary.
If users move a polyline boundary, all the tiles should be
erased, then redrawn in the new location. This is a fairly simple
operation, because the polyline boundary did not change its size or
If users scale a polyline boundary, you need to make a
decision. Should the tiles be scaled up as well, so that the path
contains the same number of tiles? Or, should the tile size remain
the same and the application add or remove tiles, depending on
whether the polyline was scaled up or down?
If users rotate a polyline boundary, all the tiles should be
erased, then redrawn in the new orientation.
though, just plan for the following:
Warn the user upon command-start that the selected edit command
(such as stretch, move, or rotate) will have
detrimental effects on a garden path.
If the user proceeds, erase the tiles and do not redraw
Remove the reactors from the path outline.
to user-invoked AutoCAD commands, entities may also be modified or
deleted through AutoLISP or ObjectARX. applications. The
example provided in the Garden Path tutorial does not cover
programmatic manipulation of the garden path polyline boundary,
such as through (entdel <polyline entity>). In this case, the editor reactor
:vlr-commandEnded will not be