Core Image Transition Parameters

[Bridger Maxwell]

Hey,
  I was playing around with Core Image transitions, and while I found the
Core Image Sampler stack very helpful, I am still a little confused about
the parameters involved in a Core Image transition.  The transition I am
using is CIRippleTransition and the line I use looks like this:
show grp "Shields" with visual effect CIRippleTransition slow with center
(175,275) and extent (0,0,0,0) and scale -10 and width 30 and shadingImage
id 2455
The "center" I found to be where the center of the transition, relative to
what is being revealed or hidden.
The "extent" I am really confused about, it looks like it might be a rect,
but I can't figure out how to work it.
The "scale" and "width" I have been able to play with until I got the
desired effect, but I honestly couldn't explain why those numbers work.
The "shadingImage" seems to be in the wrong format any time I pass it
anything except an empty image.  What should a proper shadingImage look like
and what format should it be in?
Really, I am trying to get the effect that OSX uses when adding a widget to
the dashboard.  If anyone knows more about this, could you please help me
out?

  Thank You,
  Bridger Maxwell
  Christa McAuliffe Space Education Center