to patch-draw
  if mouse-down?     ;; reports true or false to indicate whether mouse button is down
    [
      ;; mouse-xcor and mouse-ycor report the position of the mouse --
      ;; note that they report the precise position of the mouse,
      ;; so you might get a decimal number like 12.3, but patch-at
      ;; automatically rounds to the nearest patch
      ask patch-at mouse-xcor mouse-ycor
        [ set pcolor red ]
    ]
end

to turtle-draw
  ifelse mouse-down?
    [ ;; first make sure there's a turtle (if the user just pressed
      ;; the mouse button, there won't be yet)
      if not any? turtles
        [ ask patch-at mouse-xcor mouse-ycor
            [ sprout 1
                [ pen-down ] ] ]
      ;; now that we're sure we have a turtle, we ask it to move
      ;; towards the mouse
      ask turtles
        [ if distancexy mouse-xcor mouse-ycor > 0
            [ set heading towardsxy mouse-xcor mouse-ycor
              fd 0.4 ] ] ]  ;; 0.4 gives nice smooth lines
    ;; once the user releases the mouse button, we don't need the
    ;; turtle anymore
    [ clear-turtles ]
end
@#$#@#$#@
GRAPHICS-WINDOW
288
10
622
365
40
40
4.0
0
10
1
1
1

CC-WINDOW
288
367
612
504
Command Center

MONITOR
138
265
226
314
NIL
mouse-ycor
3
1

MONITOR
49
265
137
314
NIL
mouse-xcor
3
1

MONITOR
83
215
188
264
NIL
mouse-down?
3
1

BUTTON
150
42
258
75
NIL
turtle-draw
T
1
T
OBSERVER
NIL

TEXTBOX
40
84
265
163
Press "patch draw" or "turtle draw", then move the mouse over the graphics window, hold down the mouse button, and move the mouse to draw.

BUTTON
36
42
145
75
NIL
patch-draw
T
1
T
OBSERVER
NIL

BUTTON
87
168
185
201
NIL
clear-patches
NIL
1
T
OBSERVER
T

@#$#@#$#@
WHAT IS IT?
------------
This demo shows how to use the MOUSE-DOWN?, MOUSE-XCOR, and MOUSE-YCOR reporters to make a model that the user can interact with using the mouse.  It also demonstrates the difference between using patches and turtles to achieve a desired effect.
@#$#@#$#@
default
true
0
Polygon -7566196 true true 150 5 40 250 150 205 260 250

circle-shape
true
0
Circle -7566196 true true 10 10 283

@#$#@#$#@
NetLogo 2.0beta5
@#$#@#$#@
@#$#@#$#@
@#$#@#$#@