TkTurtle v1.0

This is a simple Logo-like turtle graphics package implemented in
Extended Tcl. It does not include any programming environment support,
everything must be done from the command line or sourced files as in
normal Tcl programming. It needs Extended Tcl, mainly for the trig
functions. It's been a long time since I've used Logo, so the style
here may be closer to the Smalltalk-80 Pen class, or the Lightspeed
Pascal turtle graphics libraries (which I used as references) than
real Logo.

TkTurtle works by making a canvas, and then defining Tcl procedures to
display a turtle, and draw patterns. No C code is included in this
package (but, of course, it currently needs Extended Tcl). There is a
fair range of turtle commands supported, with the exception of real
colour: the colour command currently uses stipple patterns. The use of
English, rather than American spellings (colour, centre) may be
considered a bug by some.

This has actually been used in anger, as part of a short course to
interest high school students in computer science. It seems fairly
stable, but, of course, this is not warranted for anything :-)

The distribution consists of one file of code (turtle), a file of
examples, and this short readme. There is no real documentation.  You
are welcome to use this as you see fit, providing the usual credit is
given to the original author.


COMMANDS

turtle		initialise the turtle library. This is the command
		that should be autoloaded, the other commands being
		loaded in the file as the package is invoked
		
go <length>	move the turtle <length> pixels 
		- a line will be draw if the pen is down

			go 20

goto <x> <y>	move the turtle to the position specified
 
		- a line will be draw if the pen is down

			goto 0 0 

write <text>	prints the <text> as a string at the current position

			write "Hello John"

up		put the pen up
		- the turtle will move without drawing

			up

down 		put the pen down 
		- the turtle will now draw lines

			down

turn <angle>	turns the turtle <angle> degrees clockwise
		- if <angle> is negative, counterclockwise

			turn 90

north		set the turtle's direction to north (270 degrees)

			north

turnto <angle>  sets the turtle's direction to be <angle>

			turnto 175

width [<n>]	with one argument (must be an integer)
			sets the width of lines the turtle will draw
		with no arguments, returns the current width

			width 3

colour [<n>]	with one argument (must be an integer)
			sets the pattern of lines the turtle will draw
		with no arguments, returns the current width

			colour 4

show		draws the turtle

			show

hide		hides the turtle - the turtle will still leave a trace
		if it is down, but won't itself be displayed - makes
		things run faster.

			hide

home		move the turtle to the center and point it north

clear		clear the screen, home the turtle, and reset colour
		and width information

screen-dump <f>	write a screen dump 
		- with no arguments, to Screen-dump.ps
		- with one argument, to that filename




EXTRA COMMANDS

move		same as go, goto, except the don't draw, and 
moveto			don't change the turtle state.

south		shortcuts for turnto 90, etc.
east
west

d2r		converts degress to radians for calling the trig
		functions	

direction	returns the turtle's direction

location	returns a two-element list, the turtle's location

slow		sets slow mode
fast		sets fast mode
speed [<bool>]	like a ZX-81, fast mode doesn't update the screen 
			after every movement.

pen [<bool>]	with no arguments, returns the pen status
		with one argumenr of 0 or 1, sets the pen status

centre		centre the screen, not the turtle 
			(use home to centre the turtle)

status	[<s>]	with no arguments, returns a six-element list
			containing turtle status
		with one argument of such a list, set status

			set saved [status] # save status
			status $saved	   # restore

window <wid>	place a window onto the canvas at the current position

new		clear, and also remove any windows



SHORTCUTS IN THE TURTLE WINDOW

Button-2	drag-scroll the window 
C		centre the window
F		toggle speed (slow mode/ fast mode)
T		toggle command tracing
S		toggle turtle display (hide/show)
C-C, C-Q	quit


TO DO LIST

* Vanilla Tcl version of TkTurtle
* Programming environment (steal from wtour?)
* Extension to multiple turtles and canvasses
* Real colour support
* Reorganise so it runs **faster**
* Don't add a new line item for each drawn segment - 
	collect line squences into large line items
* fix it so everything worked in degrees (no need for d2r)

Suggestion, comments, etc, are always apprecitated

James Noble
kjx@comp.vuw.ac.nz