Turtle Graphics Applet

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TurtleGraphics Programming Environment Applet

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TG is a Logo programming environment which provides a
command line interface to a Java-based implementation
of a subset of Berkeley Logo with some Jave extensions.

Most of this Help message has been taken from Brian
Harvey's documentation of Berkeley Logo, from Computer
Science Logo Style, Brian Harvey, The MIT Press, 1997.
Brian has kindly provided Berkeley Logo under the GNU
General Public License.  Thank you, Brian!

The center of the graphics window is turtle location
0,0.  Positive X is to the right; positive Y is up.
Headings (angles) are measured in degrees clockwise
from the positive Y axis. (This differs from the
common mathematical convention of measuring angles
counterclockwise from the positive X axis.)  The
turtle is represented as a hexagon with head, legs
and a tail; the actual turtle position is in the
middle of the turtle.

 AND trueFalse1 trueFalse2
    Outputs true if trueFalse1 AND trueFalse2 are
    true, otherwise it outputs false.

    Example:
    IF AND EQUAL? XCOR 0 EQUAL? YCOR 0 PRINTLN "Home

 BF word-or-sentence
 BUTFIRST word-or-sentence
    If the input is a word, all characters except its
    first are output. If the input is a sentence, all
    words except the first are output.

 BK number
 BACK number
    Moves the turtle backward, i.e., exactly
    opposite to the direction that it's facing,
    by the specified number of turtle steps.
         
    Example: BACK 150

 BL word-or-sentence
 BUTLAST word-or-sentence
    If the input is a word, all characters except its
    last are output. If the input is a sentence, all
    words except the last one are output.
  
 CG
 CLEAN
    Erases everything that the turtle has drawn in the
    graphics window.  The turtle's state (position,
    heading, pen color, etc.) is not changed.

 COS number
    Outputs the cosine of number, which is degrees.

 COUNT word-or-sentence
    If the input is a word, the number of characters
    in it is output. If the input is a sentence, the
    number of words in it is output.

 CT
 CLEARTEXT
    Erases all of the text in the terminal window.

 DIFFERENCE number1 number2
    Outputs the result of subtracting number2 from
    number1.

    Example: DIFFERENCE 15 7

 EQUAL? value1 value2
 EQUALP value1 value2
    If value1 is equal to value2, true is output;
    otherwise false is output.

    Example: EQUAL? MOUSEX 0

 EMPTY? word-or-sentence
 EMPTYP word-or-sentence
    Outputs true if its input is a word that has no
    characters in it, otherwise false. Outputs true
    if its input is a sentence that has no words in
    it, otherwise false.

 FD number
 FORWARD number
    Moves the turtle forward, in the direction it is
    facing, by the specified number of turtle steps.

    Example: FORWARD 100

 FILL
    Whatever color is under the turtle is changed to
    the turtle's color, and this process is repeated
    in an outward manner for all pixels that are
    neighbors and match the original color.

 FIRST word-or-sentence
    If the input is a word, its first character is
    output. If the input is a sentence, its first
    word is output.

 GREATER? value1 value2
 GREATERP value1 value2
    If value1 is greater than value2, true is output;
    otherwise false is output.

    Example: GREATER? MOUSEX 0

 HEADING
    Outputs the turtle's heading (degrees).

    Example: PRINTLN HEADING

 HT
 HIDETURTLE
    Makes the turtle invisible.
  
 HOME
    Moves the turtle to the center of the graphics
    window, i.e., coordinates 0,0.
     
 IF boolean [ instructions ]
    The instructions enclosed in the square brackets
    are performed if the boolean value is true,
    nothing is done if it's false.  The boolean
    value must be either true or false.

    Example: IF LESS? :INPUT 0 [ STOP ]

 ITEM number word-or-sentence
    Outputs the number-th element of its second input.
    If its second input is a word, it outputs a word
    consisting on the number-th character. If its
    second input is a sentence, it outputs the
    number-th word of it.

 KEYPRESSED
    If a user-defined procedure with the name KEYPRESSED,
    expecting one input, has been defined, it is performed when
    a key is depressed while the graphics canvas has focus.

    Example: TO keyPressed :keyNum
               PRINTLN SENTENCE "keyPressed= :keyNum
               END

    Key numbers are:

     Number    Character Key           Number   Action Key
    --------   ----------------        ------   -----------
        8      Backspace                65536   Up Arrow
        9      Tab                      65537   Down Arrow
       10      Enter                    65538   Left Arrow
       27      Esc                      65539   Right Arrow
    32 - 127   ASCII Characters         65540   Alt
                                        65541   Control
                                        65542   Shift

 LABEL word
 LABEL sentence
    The text representing LABEL's input is drawn in
    the graphics window.

 LAST word-or-sentence
    If the input is a word, its last character is
    output. If the input is a sentence, its last
    word is output.

 LESS? value1 value2
 LESSP value1 value2
    If value1 is less than value2, true is output;
    otherwise false is output.

    Example: LESS? MOUSEX 0

 LT number
 LEFT number
    Turns the turtle counterclockwise by the
    specified angle measured by a number of degrees
    (1/360 of a circle).

    Example: LEFT 180

 MAKE name value
    Creates a variable named name if it doesn't
    already exist.  The contents of the variable
    is set to value.

    Example: MAKE "WHITE 7

 MEMBER? character word
 MEMBER? word sentence
 MEMBERP character word
 MEMBERP word sentence
    Outputs true if its first input is in its second
    input, otherwise it outputs false.

 MINUS number
    Outputs the negative of number.

    Example: MINUS 10

 MOUSECLICK
    When a mouse-click (left button) is received by
    TG, it invokes a user-defined procedure with the
    name MOUSECLICK, if one has been defined.

    Example: TO mouseclick
               PRINTLN "mouseclick
               END

 MOUSEX
    Outputs the X-coordinate where the mouse was
    when it was last clicked.

 MOUSEY
    Outputs the Y-coordinate where the mouse was
    when it was last clicked.

 NOT trueFalse
    Outputs false if trueFalse is true, else false.

 OR trueFalse1 trueFalse2
    Outputs true if trueFalse1 OR trueFalse2 is true,
    otherwise it outputs false.

    Example:
    IF OR EQUAL? XCOR 0 EQUAL? YCOR 0 PRINTLN [On Axis]

 OUTPUT value
    The current invocation of the procedure in which
    OUTPUT exists is teminated and value is output.

    Example: TO randomColor
               OUTPUT RANDOM 16
               END

 PD
 PENDOWN
    Puts the turtle's pen down so that it leaves a
    trace when it moves.

 PP
 PRINTPROCS
    Displays the names and inputs of all the user-
    defined procedures in the terminal window.

 PRINTLN word
 PRINTLN sentence
    The text representing PRINTLN's input is drawn
    in the terminal window.

 PRODUCT number1 number2
    Outputs the result of multiplying number1 by
    number2.

    Example: PRODUCT 64 8

 PT
 PRINTTEXT name
    Displays the source code representation of
    the user-defined procedure named name in the
    terminal window.

 PU
 PENUP
    Lifts the turtle's pen up so that it leaves no
    trace when it moves.

 QUOTIENT number1 number2
    Outputs the result of dividing number1 by number2.

    Example: QUOTIENT 16384 4096

 RANDOM number
    Outputs some integer greater-than or equal-to
    zero AND less-than number.

    Example: RANDOM 16

 REMAINDER number1 number2
    Output the remainder left after dividing number1
    by number2. Number1 and number2 must be integers.

    Example: REMAINDER 1234 10

 REPEAT number [ instructions ]
    Repeats the instructions enclosed in the square
    brackets the specified number of times.

    Example: REPEAT 4 [ FD 100 RT 90 ]

 ROUND number
    Outputs the closest integer to number.

    Example: ROUND 22.45

 RT number
 RIGHT number
    Turns the turtle clockwise by the specified angle,
    measured in degrees (1/360 of a circle).
         
    Example: RIGHT 90

 SENTENCE word word
 SENTENCE word sentence
 SENTENCE sentence word
 SENTENCE sentence sentence
    Outputs a sentence consisting of its first input
    concatenated with its second input.
  
 SETC number
 SETPC number
 SETPENCOLOR number
    Sets the turtle's color - the color of its pen.
    Color is expressed as a number.  The available
    colors are:

    Number  Color       Number  Color
    ------  -------     ------  -------
       0    black          8    brown
       1    blue           9    tan
       2    green         10    forest
       3    cyan          11    aqua
       4    red           12    salmon
       5    magenta       13    purple
       6    yellow        14    orange
       7    white         15    grey
         
    Example: SETC 10
  
 SETH number
 SETHEADING number
    Turns the turtle to a new absolute heading.
    The input, number, is the heading in degrees
    clockwise from the positive Y axis, i.e.,
    0 is due North (up),
    90 is due East (right),
    180 is due South (down), and
    270 is due West (left). 
         
    Example: SETH 90

 SETLH number
 SETLABELHEIGHT number
    The height of characters drawn with the LABEL
    procedure is set to the input.

    Example: SETLABELHEIGHT 24
  
 SETPS number
 SETPENSIZE number
    Sets the width of the turtle's pen, which
    determines the thickness of the trace it leaves,
    the line it draws.
         
    Example: SETPENSIZE 5
  
 SETX number
    Moves the turtle horizontally to the specified
    absolute window position.
         
    Example: SETX 100
  
 SETXY number1 number2
    Moves the turtle to an absolute window position,
    which is two numbers: the new horizontal (X) and
    vertical (Y) coordinates.

    Example: SETXY 50 -30 
  
 SETY number
    Moves the turtle vertically to the specified
    absolute window position.  

    Example: SETY 100

 SIN number
    Outputs the sine of number which is in degrees.

    Example: SIN 45

 SQRT number
    Outputs the square root of number.

    Example: SQRT 64

 ST
 SHOWTURTLE
    Makes the turtle visible.

 STOP
    The current invocation of the procedure in which
    STOP exists terminates.

    Example: IF EQUAL? :input 0 [STOP]

 SUM number1 number2
    Outputs the result of adding number1 and number2.

    Example: SUM 123 456

 WAIT number
    Execution of the program is suspended for number
    of milliseconds (1/1000 of a second).

 WORD word word
    Outputs a word consisting of its first input
    concatenated with its second input.

 XCOR
    Outputs the turtle's X coordinate.

    Example: MAKE "curX XCOR

 YCOR
    Outputs the turtle's Y coordinate.

    Example: LABEL YCOR


See Appendix J for the application version of this applet as well as all of its source code.

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