breed [ lights light ]
breed [ moths moth ]

globals
[
  scale-factor  ;; to control the form of the light field
]

lights-own
[
  intensity
]

moths-own
[
  ;; +1 means the moths turn to the right to try to evade a bright light
  ;; (and thus circle the light source clockwise). -1 means the moths
  ;; turn to the left (and circle the light counter-clockwise)
  ;; The direction tendency is assigned to each moth when it is created and does not
  ;; change during the moth's lifetime.
  direction
]

patches-own
[
  light-level ;; represents the light energy from all light sources
]

to setup
  clear-all
  set-default-shape lights "circle 2"
  set-default-shape moths "butterfly"
  set scale-factor 50
  if number-lights > 0
  [
    make-lights number-lights
    ask patches [ generate-field ]
  ]
  make-moths number-moths
  reset-ticks
end

to go
  ask moths [ move-thru-field ]
  tick
end

;;;;;;;;;;;;;;;;;;;;;;
;; Setup Procedures ;;
;;;;;;;;;;;;;;;;;;;;;;

to make-lights [ number ]
  create-lights number [
    set color white
    jump 10 + random-float (max-pxcor - 30)
    set intensity random luminance + 20
    set size sqrt intensity
  ]
end

to make-moths [ number ]
  create-moths number [
    ifelse (random 2 = 0)
      [ set direction 1 ]
      [ set direction -1 ]
    set color white
    jump random-float max-pxcor
    set size 5
  ]
end

to generate-field ;; patch procedure
  set light-level 0
  ;; every patch needs to check in with every light
  ask lights
    [ set-field myself ]
  set pcolor scale-color blue (sqrt light-level) 0.1 ( sqrt ( 20 * max [intensity] of lights ) )
end

;; do the calculations for the light on one patch due to one light
;; which is proportional to the distance from the light squared.
to set-field [p]  ;; turtle procedure; input p is a patch
  let rsquared (distance p) ^ 2
  let amount intensity * scale-factor
  ifelse rsquared = 0
    [ set amount amount * 1000 ]
    [ set amount amount / rsquared ]
  ask p [ set light-level light-level + amount ]
end

;;;;;;;;;;;;;;;;;;;;;;;;
;; Runtime Procedures ;;
;;;;;;;;;;;;;;;;;;;;;;;;

to move-thru-field    ;; turtle procedure
  ifelse (light-level <= ( 1 / (10 * sensitivity) ))
  [
    ;; if there is no detectable light move randomly
    rt flutter-amount 45
  ]
  [
    ifelse (random 25 = 0)
    ;; add some additional randomness to the moth's movement, this allows some small
    ;; probability that the moth might "escape" from the light.
    [
      rt flutter-amount 60
    ]
    [
      ;; turn toward the brightest light
      maximize
      ;; if the light ahead is not above the sensitivity threshold  head towards the light
      ;; otherwise move randomly
      ifelse ( [light-level] of patch-ahead 1 / light-level > ( 1 + 1 / (10 * sensitivity) ) )
      [
        lt ( direction * turn-angle )
      ]
      [
        rt flutter-amount 60
      ]
    ]
  ]
  if not can-move? 1
    [ maximize ]
  fd 1
end

to maximize  ;; turtle procedure
  face max-one-of patches in-radius 1 [light-level]
end

to-report flutter-amount [limit]
  ;; This routine takes a number as an input and returns a random value between
  ;; (+1 * input value) and (-1 * input value).
  ;; It is used to add a random flutter to the moth's movements
  report random-float (2 * limit) - limit
end


; Copyright 2005 Uri Wilensky.
; See Info tab for full copyright and license.