Bounce Ex

to setup
  clear-all
  set-default-shape turtles "circle"
  draw-walls
  create-turtles 5                      ;; create some turtles
    [ randomize ]                       ;; place them randomly
  reset-ticks
end 

; draws the boundaries (walls) of the "billiard table"

to draw-walls
  ; draw left and right walls
  ask patches with [abs pxcor = max-pxcor]
    [ set pcolor blue ]
  ; draw top and bottom walls
  ask patches with [abs pycor = max-pycor]
    [ set pcolor blue ]
end 

; set random location

to randomize
  setxy random-xcor random-ycor
  if pcolor = blue       ; if it's on the wall...
    [ randomize ]        ; ...try again
end 

to go
  ask turtles [
    ifelse leave-trace?             ;; the turtle puts its pen up or down depending on the
      [ pen-down ]                  ;;   value of the LEAVE-TRACE? switch
      [ pen-up ]
    bounce
    fd 0.1
  ]
  tick
end 

;; this procedure checks the coordinates and makes the turtles
;; reflect according to the law that the angle of reflection is
;; equal to the angle of incidence

to bounce  ;; turtle procedure
  ; check: hitting left or right wall?
  if abs [pxcor] of patch-ahead 0.1 = max-pxcor
    ; if so, reflect heading around x axis
    [ set heading (- heading) ]
  ; check: hitting top or bottom wall?
  if abs [pycor] of patch-ahead 0.1 = max-pycor
    ; if so, reflect heading around y axis
    [ set heading (180 - heading) ]
end 


; Public Domain:
; To the extent possible under law, Uri Wilensky has waived all
; copyright and related or neighboring rights to this model.