 # constants
-qt  = Math.PI / 2
-tau = Math.PI * 2
+pi  = Math.PI
+qt  = pi / 2
+tau = pi * 2
 
 # general handle on everything; keeps track of geometry of entities it contains
 class Universe

  h = Math.sqrt( x*x + y*y )
  theta = Math.acos( a / h )
  if x < 0
    if y < 0 then Math.PI + theta else Math.PI - theta
  else
    if y < 0 then 2 * Math.PI - theta else theta

grep = ( ar, f ) ->
  x for x in ar when f(x)

      @topic.topicColor  = @outline
      @topic.inheritMark = false
      @draw()
      @topic.cell.draw()
  # highlight an organism by coloring its belly
  highlight: ( x, y, color, inherit ) ->
    for t in @thingsAt( x, y ) when t instanceof Organism
