Stumped & Feeling Stupid...

[Judy Perry]

I'm trying to create a simple sidescroller game example.  I have a stack
containing a single card containing two images:

(1) "map" image that is larger than card window (it's a starcraft map).
(2) animated gif of player/critter that can be moved about screen using
the arrow keys.

The map is more or less scrollable by using global variables to reset its
position when the critter intersects with transparent buttons on the
card's edges (incomplete but working acceptably so far). The location of
the critter is also kept via global variables.

Among other things, I'm trying to test for the critter hitting an obstacle
such that s/he/it can't "go" certain places (which I'll call
"Obstacle1.gif")

I'm trying to keep track of the lastXposition and lastYposition via global
variables but it doesn't seem to be working in terms of constraining the
critter's movement; I've checked the variable watcher and, indeed, the
globals for lastXposition and lastYposition aren't changing in value, but
the critter's location is, even though it is set to
lastXposition,lastYposition.

Any ideas?  Script is below...

Thank you for any ideas anyone can offer!

Judy

global theXcoord, theYcoord, mapXcoord, mapYcoord, lastXPosition,
lastYposition
on preOpenCard
  put 550 into mapYcoord
  put 412 into mapXcoord
  set the loc of image "GeminiStation.jpg" to mapXcoord,mapYcoord
end preOpenCard


on openCard
  put "80" into theXcoord
  put "80" into lastXposition
  put "155" into theYcoord
  put "155" into lastYposition
  set the loc of image "Lurker.gif" to theXcoord,theYcoord

end openCard

on arrowKey tKey
  switch tKey
  case "left"
    subtract "7" from theXcoord
   put (theXcoord + 7) into lastXposition
    break
  case "right"
    add 7 to theXcoord
    put (theXcoord - 7) into lastXposition
    break
  case "up"
    subtract 7 from theYcoord
    put (theYcoord + 7) into lastYposition
    break
  case "down"
    add 7 to theYcoord
    put (theYcoord - 7) into lastYposition
    break
  end switch
obstacleDetect
  set the loc of image "Lurker.gif" to theXcoord,theYcoord
   edgeDetect

end arrowKey

on edgeDetect
  if the intersect (image "Lurker.gif",button "RightEdge")  then
    subtract 13 from mapXCoord
    set the loc of image "GeminiStation.jpg" to mapXcoord,mapYcoord
  end if
  if the intersect (image "Lurker.gif",button "BottomEdge")  then
    subtract 13 from mapYcoord
    set the loc of image "GeminiStation.jpg" to mapXcoord,mapYcoord
  end if
  if the intersect (image "Lurker.gif",button "Corner")  then
    subtract 13 from mapXcoord
    subtract 13 from mapYcoord
    set the loc of image "GeminiStation.jpg" to mapXcoord,mapYcoord
  end if


end edgeDetect

on obstacleDetect
  --repeat for i = 1 to 10
    if the intersect (image "Lurker.gif",image "Obstacle1.gif")  then
      beep
    set the loc of image "Lurker.gif" to lastXposition,lastYposition
  end if

end obstacleDetect