Turtle3d

Turtle3d is a 3-dimensional turtle graphics package with your choice of Logo, Python or Tcl interface. Download it here.

To build, check that the X11_HOME and OPENGL_HOME variables at the top of Makefile are correct for your system, and then type "gmake". It's been tested on Linux and FreeBSD.

To start the Python version, type this at the shell prompt:

% python -i turtle.py

A window should pop up now, with a pointy triangle (the "turtle") in the middle of that window.

And then a sample session might look like this:

>>> fd(50)
>>> rt(90)
>>> fd(45)
>>> up(120)
>>> rl(45)
>>> fd(60)

The names of the commands are inspired by Logo's -- fd=forward, bk=backward, rt=right, lt=left, pu=pen-up, pd=pen-down. In addition, you can pitch the turtle up (up) or down (dn), and roll it (rl -- there's no "left roll", just roll by a negative number of degrees).

Use your mouse to rotate (left button + drag), pan (middle button) and zoom (right button) the image.

Walking on a sphere

The turtle can be constrained to the surface of a sphere. To do that, use sfd instead of fd and sbk instead of bk (and don't use rl, up or dn at all!) The units of sfd and sbk are degrees.

There is no "sphere mode"; you can type sfd and then fd anywhere and anytime you want. However, sfd always assumes the turtle is currently on the surface of a sphere. So, in a sequence of commands such as

>>> sfd(90)
>>> fd(100)
>>> sfd(90)

the first and second sfd's will each trace one quarter of a great circle, but they will not lie on the same sphere.

If you want to see a shaded blue sphere like the one at right, give the following commands:

>>> sphere(1)
>>> lighting(1)

Other interfaces

Tcl

To start the Tcl version, start tclsh and then your first command to the Tcl interpreter should be "source turtle.tcl". At this point, the commands look just like the Python commands except instead of parentheses use spaces, i.e. "fd 50", "rt 90", etc.

minimalistic

The executable you have built -- draw -- reads Logo-style turtle commands from standard input. Thus the following could be considered the minimal interface:

% cat | ./draw
fd 50
lt 120
pu

And less minimal but still quite spare:

% sh | ./draw
for i in 1 2 3 4 5
do
echo fd 50
echo rt 75
done

Logo

I've saved this part for last because getting to a Logo interface takes some doing.

Grab the source code to ucblogo 5.1 and unpack it. (I'm storing it here because the most recent version is now up to 5.3 and I'm not inclined to try tracking that.)
Apply the patchfile -- that's the file readline-popen-patchfile you find in turtle3d.tar.gz. (Copy the patchfile to the ucblogo directory and type "patch < readline-popen-patchfile".) The patchfile does two things, one just a convenience, the other essential:
- It puts GNU readline support into ucblogo. That's the convenience. If you don't want readline, or you don't have the readline library and header files on your development system, or you do but there's some problem, you can delete from readline-popen-patchfile the sections that refer to the file "parse.c" and the file "configure".
- It introduces a popen function into ucblogo. This is the essential part.
Build the patched ucblogo with the standard "./configure; make; make install" sequence. (Note it won't start if you don't say "make install"; not sure why this is...)
With "turtle3d" as your current working directory and "logo" on your PATH, start up like this:
```
logo turtle3d.lg
```
This should bring up the OpenGL window -- not Logo's graphics window but the window that's produced by the "draw" executable. You're now off and running. You have the standard Logo turtle commands fd, bk, rt, lt, pu, pd, ht, st as well as the 3-D ones up, dn, rl and the spheroidal sfd and sbk. To bring up the blue sphere type lighting 1 sphere 1.

Further features of the Python interface

You can write a file of Python functions that use the turtle commands. The file examples.py shows how this might be done. To use the functions from examples.py, it's necessary to start up a little differently. Your shell command should no longer be "python -i turtle.py" but rather

% python

and then, at the Python interpreter prompt, type

>>> from turtle import *
>>> turtleInit()
>>> import examples

then execute one of the functions from examples.py as follows:

>>> examples.randwalk3d()

And we can go even more automated than that. Have a look at the file callexamples.py, and then, at the shell prompt, type

% python callexamples.py

Reference

Abelson, Harold and Andrea diSessa, Turtle geometry : the computer as a medium for exploring mathematics, Cambridge, MA : MIT Press, 1981.

Author: Ted Sternberg