Updating gp:Calculate-and-Draw-Tiles

Earlier in this lesson, it was noted that you need to force gp:Calculate-and-Draw-Tiles to use ActiveX to create objects when invoked from a reactor callback. This means overriding the object creation style (ActiveX, entmake, or command) chosen by the user, if necessary. The code you just updated, in the gp:command-ended function, contains the following invocation of the tile drawing routine:

(setq tileList (gp:Calculate-and-Draw-Tiles
	;; path data list without correct tile list.
	;; Object creation function.
	;; Within a reactor this *MUST* be ActiveX.

Two parameters are passed to gp:Calculate-and-Draw-Tiles: NewReactorData (which is a list in the form of the original gp_PathData association list) and the string "ActiveX" (which will set the object creation style). But take a look at the current definition of gp:Calculate-and-Draw-Tiles. (In case you have forgotten, this function is defined in gpdraw.lsp.) Here is the part of the function that declares the parameters and local variables:

(defun gp:Calculate-and-Draw-Tiles (BoundaryData /
	 PathLength		TileSpace
	 TileRadius		SpaceFilled
	 SpaceToFill		 RowSpacing
	 offsetFromCenter	rowStartPoint
	 pathWidth		 pathAngle
	 ObjectCreationStyle TileList)

Notice only that one parameter is currently specified, and ObjectCreationStyle is identified as a local variable. Review how the ObjectCreationStyle variable is set, which is a little farther into the function:

(setq ObjectCreationStyle (strcase (cdr (assoc 3 BoundaryData))))

The ObjectCreationStyle is currently set internally within the function by retrieving the value tucked away in the BoundaryData variable (the association list). But now you need to be able to override that value.

To modify gp:Calculate-and-Draw-Tiles to accept an object creation style argument

  1. Add the ObjectCreationStyle variable to the function argument.
  2. Remove ObjectCreationStyle from the local variables.

    The defun statement for the function should look like the following:

    (defun gp:Calculate-and-Draw-Tiles (BoundaryData 
    	/ PathLength	 TileSpace
    	TileRadius	 SpaceFilled
    	SpaceToFile	RowSpacing
    	offsetFromCenter   rowStartPoint
    	pathWidth   pathAngle
    	TileList)		 ; remove ObjectCreationStyle from locals

    Note that if you declare a variable both as a parameter (before the slash) and as a local variable (after the slash), VLISP will point this out to you. For example, if you declare ObjectCreationStyle as both a parameter and a variable, then use the VLISP syntax checking tool on the gp:Calculate-and-Draw-Tiles function, the following message will appear in the Build Output window:

    ; *** WARNING: same symbol before and after / in arguments list: OBJECTCREATIONSTYLE
  3. Modify the first setq expression within gp:Calculate-and-Draw-Tiles so that it looks like the following:
       PathLength  (cdr (assoc 41 BoundaryData))
       TileSpace   (cdr (assoc 43 BoundaryData))
       TileRadius  (cdr (assoc 42 BoundaryData))
       SpaceToFill (- PathLength TileRadius)
       RowSpacing (* (+ TileSpace (* TileRadius 2.0))
    	(sin (Degrees->Radians 60))
       SpaceFilled RowSpacing
       offsetFromCenter 0.0
       offsetDistance  /(+(* TileRadius 2.0)TileSpace)2.0)
       rowStartPoint  cdr (assoc 10 BoundaryData))
       pathWidth	cdr (assoc 40 BoundaryData))
       pathAngle	cdr (assoc 50 BoundaryData))
    ) ;_ end of setq
     (if (not ObjectCreationStyle)
       (setq ObjectCreationStyle (strcase (cdr (assoc 3 BoundaryData))))

    The original assignment statement for ObjectCreationStyle has been removed. The code now checks to see if a value has been provided for ObjectCreationStyle. If ObjectCreationStyle is not set (that is, the value is nil), the function assigns it a value from the BoundaryData variable.

    There is one more series of changes you need to make to gp:Calculate-and-Draw-Tiles.