Constraining the pointer

[Cubist at aol.com]

sez wouter.abraham at scarlet.be:
>On 22 Apr 2005, at 11:53, David Glasgow wrote:
>> I have an assessment that may be used with people with significant 
>> motor skills problems.  At a point when they have to use a rating 
>> scale I constrain the pointer so it can't 'fall' of the scale.
>I don't know in which kind of control structure you used the code above,
>but I changed it a bit and put it inside a mousemove handler.
>The code seems to work without jerks or delayed mousemovements or extra
>overhead:
>
>on mousemove x,y
>   get rect of fld "container"
>   if x,y is not within it then
>     if x  <  item 1 of it  then put (item 1 of it + 4) into tX --left
>of field "container"
>     else if  x  >  item 3 of it  then put (item 3 of it - 4) into tX 
>--right of field "container"
>     else put x into tX
>     if y  >  item 4 of it   then put (item 4 of it  - 4) into  tY  
>--bottom of field "container"
>     else if y <  item 2 of it  then put (item 2 of it  + 4) into tY 
>--top of field "container"
>     else put y into tY
>     put (left of this stack) + tX into item 1 of tLoc
>     put (top of this stack) + tY into item 2 of tLoc
>     set the screenmouseloc to tLoc
>   end if
>end mousemove
   I don't believe that mega-IF statement is truly necessary. Try this 
instead:

on mouseMove X,Y
  put the rect of fld "container" into Fred
  put min (item 3 of Fred - 4, max (item 1 of Fred + 4, X)) into X
  put min (item 4 of Fred - 4, max (item 2 of Fred + 4, Y)) into Y
  set the screenMouseLoc to (X,Y)
end mouseMove

   If the mouseLoc is within the specified rectangle, the mouse's X co-ord 
will be less than item 3 of the rect, and greater than item 1 of the rect. Thus, 
max (item 1 of rect, the mouse X) will always result in a number *at least* 
as large as that item 1, and min (item 3 of rect, the mouse Y) will always 
result in a number *no greater than* that item 3. Plug the results of the max into 
a min (sorry about how that sounds, but you get the idea, right?), and you 
end up with a number that *must* be somewhere between item 1 of the rect and 
item 3 of the rect.
   Something similar applies to the mouse's Y co-ord, and items 2 and 4 of 
the rect.

   Hope this helps...