globals
[
  text        ;; text to be written
  left-edge   ;; pxcor of leftmost column where letters can go
  right-edge  ;; ditto for rightmost
]

turtles-own
[ 
  word-length ;; the length of the word the turtle is in
  num-word    ;; the number the turtle's word is in the text
  leader      ;; the turtle with the character before this turtle's character
  new-line?   ;; whether we should start a new line or not
]

;; setup the variables and the Graphics Window
to setup
  ca
  set text "These are the times that try men's souls. " +
           ;; the next two sentences each contain all 26
           ;; letters of the alphabet!  (which makes them
           ;; good for testing typewriters)
           "The quick brown fox jumped over the lazy dog. " +
           "Pack my box with five dozen liquor jugs."
  draw-margins
  ;; make the turtles "disappear" using a shape that has nothing
  ;; in it.  we can't use hide-turtle since we want to be able to see the
  ;; turtle's label
  set-default-shape turtles "blank"
  ;; create enough turtles to have one for every character in text
  cct (length text)
  [
    set word-length 0
    set leader nobody
    set new-line? false
    scatter
  ]
  setup-letters
end

to scatter  ;; turtle procedure
  setxy random-float screen-size-x
        random-float screen-size-y
end

to draw-margins
  ask patches
    [ ifelse (pxcor = left-margin - screen-edge-x) or
             (pxcor = screen-edge-x - right-margin)
        [ set pcolor red ]
        [ set pcolor black ] ]
end

;; assign the letters to the turtles, determine who leads them,
;; and set how long each word is
to setup-letters
  locals
  [
    remaining-text
    word-count
    prev-letter
    turtles-in-word
    index
  ]
  
  set remaining-text text
  set word-count 1
  set prev-letter nobody
  
  ask turtles
  [
    without-interruption
    [
      set label first remaining-text
      set leader prev-letter
      set num-word word-count
      if label = " "
      [
        set word-count word-count + 2
        set num-word num-word + 1
      ]
      set remaining-text but-first remaining-text
      set prev-letter self
    ]
  ]
  
  set index 1
  repeat word-count
  [
    set turtles-in-word turtles with [num-word = index]
    ask turtles-in-word
      [ set word-length count turtles-in-word ]
    set index index + 1
  ]
end

;; the main procedure called by the GO forever button
to go
  update-margins
  ask turtles
  [
    set new-line? false
    pick-heading  ;; choose the heading to the appropriate patch
    ;; if the turtle is not satisfied with where it is in 
    ;; relation to its leader, go forward a bit
    ifelse happy?
      [ setxy pxcor pycor ]  ;; move to center of patch 
      [ fd 0.5 ]
  ]
end

;; updates the left-edge and right-edge variables to match the margin
;; sliders, and redraws the margins if necessary
to update-margins
  if left-edge != left-margin - screen-edge-x + 1
    [ set left-edge left-margin - screen-edge-x + 1
      draw-margins ]
  if right-edge != screen-edge-x - right-margin - 1
    [ set right-edge screen-edge-x - right-margin - 1
      draw-margins ]
end

;; set the heading of the turtle to the appropriate patch
to pick-heading
  locals [target-patch]
  ifelse leader = nobody
    ;; first letter goes to upper-leftmost patch
    [ set target-patch patch left-edge screen-edge-y
      if distance target-patch > 0
        [ set heading towards-nowrap target-patch ] ]
    ;; other patches head toward patch to the right of leader's patch
    [
      set target-patch value-from leader [patch-at 1 0]
      if distance target-patch > 0
        [ set heading towards-nowrap target-patch ]
      ifelse right-edge - left-edge < word-length
      [
        ;; if our word is too long for the width of text,
        ;; check to see if the patch to the right of the leader is on or over
        ;; the right margin
        if pxcor-of leader >= right-edge
        [
          ;; if it is change the heading to the beginning of the next line
          set new-line? true
          set target-patch patch left-edge new-line-pycor
          if distance target-patch > 0
            [ set heading towards-nowrap target-patch ]
        ]
      ]
      [
        ;; if our word is short enough to fit on a single line but there is not
        ;; enough room on this particular line, try to word wrap.  that is to say,
        ;; if the turtle is at the beginning of a word and the word is too long to
        ;; be completed on a single line given the starting point of the word, 
        ;; have the leader of the word, move to the next line.
        if (num-word != num-word-of leader) and
           (pxcor-of leader + word-length >= right-edge)
        [
          ;; if it is change the heading to the beginning of the next line
          set new-line? true
          set target-patch patch left-edge new-line-pycor
          if distance target-patch > 0
            [ set heading towards-nowrap target-patch ]
        ]
      ]
  ]
end

;; reports pycor of the new line the turtle is supposed to go to
;; based on the location of its leader and the width of the text
to-report new-line-pycor  ;; turtle procedure
  ifelse abs (pycor-of leader - line-spacing) > screen-edge-y
    [ report pycor-of leader ]
    [ report pycor-of leader - line-spacing ]
end

;; reports true if turtle is satisifed with its current position
to-report happy?  ;; turtle procedure
  if leader = nobody  ;; if the turtle is the first letter...
    ;; ...is it on the upper-left-most patch that it can be?
    [ report (pxcor = left-edge) and (pycor = screen-edge-y) ]  
  ifelse new-line?  ;; do we want to start a new-line?
    ;; is the turtle at the beginning of the next line?
    [ report (pxcor = left-edge) and (pycor = new-line-pycor) ]
      ;; is the turtle on the patch to the right of its leader?
    [ report patch-at -1 0 = value-from leader [patch-here] ]
end


; *** NetLogo Model Copyright Notice ***
;
; This model was created as part of the project: CONNECTED MATHEMATICS:
; MAKING SENSE OF COMPLEX PHENOMENA THROUGH BUILDING OBJECT-BASED PARALLEL
; MODELS (OBPML).  The project gratefully acknowledges the support of the
; National Science Foundation (Applications of Advanced Technologies
; Program) -- grant numbers RED #9552950 and REC #9632612.
;
; Copyright 1998 by Uri Wilensky. All rights reserved.
;
; Permission to use, modify or redistribute this model is hereby granted,
; provided that both of the following requirements are followed:
; a) this copyright notice is included.
; b) this model will not be redistributed for profit without permission
;    from Uri Wilensky.
; Contact Uri Wilensky for appropriate licenses for redistribution for
; profit.
;
; This model was converted to NetLogo as part of the project:
; PARTICIPATORY SIMULATIONS: NETWORK-BASED DESIGN FOR SYSTEMS LEARNING IN
; CLASSROOMS.  The project gratefully acknowledges the support of the
; National Science Foundation (REPP program) -- grant number REC #9814682.
; Converted from StarLogoT to NetLogo, 2001.  Updated 2003.
;
; To refer to this model in academic publications, please use:
; Wilensky, U. (1998).  NetLogo Wandering Letters model.
; http://ccl.northwestern.edu/netlogo/models/WanderingLetters.
; Center for Connected Learning and Computer-Based Modeling,
; Northwestern University, Evanston, IL.
;
; In other publications, please use:
; Copyright 1998 by Uri Wilensky.  All rights reserved.  See
; http://ccl.northwestern.edu/netlogo/models/WanderingLetters
; for terms of use.
;
; *** End of NetLogo Model Copyright Notice ***
@#$#@#$#@
GRAPHICS-WINDOW
258
10
645
418
14
14
13.0
1
10
1
1
1

CC-WINDOW
3
239
252
417
Command Center

SLIDER
44
118
216
151
line-spacing
line-spacing
1
3
2
1
1
NIL

BUTTON
74
74
197
107
Scatter Letters
scatter
NIL
1
T
TURTLE
T

BUTTON
138
36
204
69
Go
go
T
1
T
OBSERVER
T

BUTTON
68
36
137
69
Setup
setup
NIL
1
T
OBSERVER
T

SLIDER
44
162
216
195
left-margin
left-margin
0
12
5
1
1
NIL

SLIDER
44
196
216
229
right-margin
right-margin
0
12
5
1
1
NIL

@#$#@#$#@
WHAT IS IT?
-----------
This model illustrates how to build a word processor where each of the letters acts independently.  Each letter knows only which letter comes before it and how long its word is.  When the letters or margins are moved, the letters find their own ways back to their proper locations.


HOW IT WORKS
------------
Each letter looks both for changes in the margins and for being out of sync with its "leader", which is the letter before it in the text.  If it is not in its proper place relative to its leader, it takes a step in its leader's direction.


HOW TO USE IT?
--------------
SETUP initializes the margins and some sample sentences for the text.

GO starts and stops the simulation.  

The LEFT-MARGIN and RIGHT-MARGIN sliders let you move the sliders.  You can move these sliders while GO is running and the letters will adjust on the fly.

SCATTER LETTERS scatters the letters randomly about the Graphics Window.  You can press this even while GO is running.

LINE-SPACING controls how much space there is between lines.


THINGS TO NOTICE
----------------
How do the letters find their way home?  In what ways is this different from the behavior of letters in a standard word processor?


THINGS TO TRY
-------------
While GO is pressed try:
--Moving the margin sliders
--Changing the spacing
--Pushing the scatter button
--Combinations of all three


EXTENDING THE MODEL
-------------------
Can you extend the model so the user can type his/her own message?  You might want to use the user-input primitive for this.

Sometimes a space will end up at the beginning of a new line.  Try to fix it so that spaces are ignored at the ends of lines.


NETLOGO FEATURES
----------------
Note the use of a blank shape to make a turtle that is invisible except for its label.




REFERENCES AND CREDITS
----------------------
This model is based on a Smalltalk program of the same name developed by Ted Kaehler of Disney Interactive.

To refer to this model in academic publications, please use: Wilensky, U. (1998).  NetLogo Wandering Letters model. http://ccl.northwestern.edu/netlogo/models/WanderingLetters. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

In other publications, please use: Copyright 1998 by Uri Wilensky.  All rights reserved.  See http://ccl.northwestern.edu/netlogo/models/WanderingLetters for terms of use.
@#$#@#$#@
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@#$#@#$#@
NetLogo 2.0beta5
@#$#@#$#@
setup
ask turtles [ scatter ]
repeat 50 [ go ]
@#$#@#$#@
@#$#@#$#@