procedure dpipe: create a decay pipeline procedure decay: mark entry for later decay
link decay
August 14, 1996; Gregg M. Townsend
Requires: Version 9 graphics
This file is in the public domain.
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.