Visual effects to scroll up a field?

[Terry Vogelaar]

Hi all,

I am working on an application for presenting text on an LCD  
projector. Not just phrases like with a normal presentation, but the  
audience actually have to read along with the (quite long) text on  
the screen. So while the people are reading along, I have to scroll  
down.

With previous solutions I just shifted, but it is annoying when the  
content just changes. "Where are we?" So now I scroll the field like  
this:

on arrowKey deze
   put the scroll of fld "tekst" into oldScroll
   switch deze
   case "down"
     put oldScroll + 300 into newScroll
     break
   end switch
   repeat with e = oldScroll to newScroll step 5
     set the scroll of fld "tekst" to e
   end repeat
end arrowKey

This does the job, but not quite smoothly.

My question is: can this be improved? Are there visual effects that  
can be applied to JUST A PART of a window - to just a field?  Any  
bright ideas to scroll a field up in a nice way? Can I use the Core  
Image capabilities of RunRev on Mac OS X 10.4 for this?

Terry