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#
#	File:     decay.icn
#
#	Subject:  Procedures for decaying-displays for windows
#
#	Author:   Gregg M. Townsend
#
#	Date:     August 14, 1996
#
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#
#   This file is in the public domain.
#
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#
#	These procedures provide a way to draw objects and then have them
#	automatically redrawn (say, in a lighter color) n steps later.
#	A user routine is called to do the actual drawing.  If a second
#	call to draw an object comes before its time has expired, the
#	object's counter is reset and the drawing routine is not called.
#
#	dpipe() initializes a decay pipeline and returns a pipeline object.
#
#	decay() marks an object, unmarks another, and advances the clock.
#
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#
#   dpipe(proc, length, gc1, gc2) -- create a decay pipeline
#
#	dpipe() initializes a decay pipeline and returns a pipeline object.
#
#	proc	user marking procedure: proc(gc, i) marks entry i using gc
#	length	length of the delay pipeline (number of steps)
#	gc1	gc to mark an entry when it becomes active
#	gc2	gc to mark an entry when it decays (becomes inactive)
#
#   decay(dp, i) -- mark entry i with later decay
#
#	decay() marks an object, unmarks another, and advances the clock.
#
#	Using decay pipe dp, entry i (anything but &null) is drawn in an
#	active state, and the oldest entry in the pipe is drawn in an
#	inactive state.
#
#	Records are kept, though, so that an already-active entry is not
#	redrawn, and a decayed entry reaching the end of the pipe is not
#	drawn as inactive if it was more recently renewed.
#
#	The decay pipe can be flushed by a sufficient number of
#	decay(dp, &null) calls.
#
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#
#  Requires:  Version 9 graphics
#
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record Decay_Rec(	# decay pipe record
   pipe,	# queue of active indices
   tab,		# table of activity for each index
   proc,	# marking procedure
   gc1,		# gc to use to turn on
   gc2)		# gc to use to turn off


##  dpipe(proc, length, gc1, gc2) -- create a decay pipeline

procedure dpipe(proc, length, gc1, gc2)		#: create a decay pipeline
   return Decay_Rec(list(length), table(0), proc, gc1, gc2)
end


##  decay(dp, i) -- mark entry i with later decay

procedure decay(dp, i)				#: mark entry for later decay
   local j
   j := get(dp.pipe)
   if (dp.tab[\i] +:= 1) = 1 then
      dp.proc(dp.gc1, i)
   if (dp.tab[\j] -:= 1) = 0 then
      dp.proc(dp.gc2, j)
   put(dp.pipe, i)
end