local sStartUpdateTime, sFrameRate, sUpdateMessageId

# start the game loop when stack opens
on preOpenStack
   set the acceleratedRendering of this stack to true
   startUpdatingTheScreen 50
end preOpenStack

# set the game loop in action
on startUpdatingTheScreen pFrameRate
   put pFrameRate into sFrameRate
   put 0 into sStartUpdateTime
   send "sendUpdateScreenMessage" to me in 0 millisecs
   put the result into sUpdateMessageId
end startUpdatingTheScreen

# cancel the game loop
on stopUpdatingTheScreen
   if sUpdateMessageId is not empty then
      cancel sUpdateMessageId
   end if
   put empty into sUpdateMessageId
end stopUpdatingTheScreen

# this handler is the "game loop" itself
on sendUpdateScreenMessage
   put the long seconds into tThisFrameTime
   
   if sStartUpdateTime is 0 then
      put the long seconds into sStartUpdateTime
   end if
   
   lock screen
   send "updateScreen" to this card
   unlock screen
   
   put the long seconds into tTheTimeNow
   
   put round((tTheTimeNow - sStartUpdateTime) * sFrameRate + 0.5) into tNextFrameCount
   send "sendUpdateScreenMessage" to me in (sStartUpdateTime + (tNextFrameCount * (1 / sFrameRate)) - tTheTimeNow) seconds
   put the result into sUpdateMessageId
end sendUpdateScreenMessage