PhysicalTurtle 0.4
Physical characteristics for turtle graphics
License: MIT License

Physical Turtle
===============

This is an extension for the Python turtle module that provides a
physical space for a turtle to inhabit. The initial aim is to provide
areas of solid space that the turtle cannot move into.

The Turtle class is extended with the following methods.  This list
may change as the first version of this package is developed.

Generally, methods are used here rather than attributes to be
consistent with the rest of the Turtle interface.

Methods:

* `touch_left()`, `touch_right()`, `touch_front()`, `touch_back()`

  Each one returns True if the Turtle would not be able to move in
  that direction.

* `last_distance()`

  The distance travelled in the preceding forward or backward
  movement. Since the turtle is not able to move through a solid area
  this distance may be less than the distance originally called for.

* `pen_set_solid()`

  Set a pen property so that any movement of the turtle with the pen
  down creates a solid area. The pen colour is not affected, so that
  the lines shown on the screen correspond to lines of solidity in
  the physical space.

  The solid area created by the turtle move is a rectangle
  corresponding to the length of the move and the width of the pen.

  No solid area is drawn in the pen is up.

  The action of filling a polygon with a colour does not create solid
  space.

* `pen_unset_solid()`

  Reverses the action of pen_set_solid so that turtle movement does
  not create solid areas.

The extension provides a new rule that says a turtle cannot cross a
line that has been drawn with `pen_set_solid`. The turtle is allowed
to move up to the solid line and the attribute `last_distance`
gives the distance actually moved.

There are two exceptions to this rule:

- A turtle with pen `up` is allowed to move anywhere. This is allows
  the turtle to move to any place on the screen and is required for
  placing the turtle into an enclosed space.

- A turtle with pen `solid` is allowed to move anywhere. This is
  specifically designed to allow drawing a solid shape where one edge
  must be drawn contiguously with another. (If this was not allowed,
  the second line would not be drawn because it would be trapped by
  the end of the first line.)

Installation
============

Get the version straight from the Python Package Index::

  pip install physicalturtle

Or Get the latest version from Bit Bucket::

    https://bitbucket.org/mikedeplume/physical-turtle

If you do download the repository, don't forget to put the
`physicalturtle` package on your PYTHON_PATH. The easiest way to do
this is to go into the directory and type::

    python setup.py install


License
=======

The package uses the MIT license:


    Permission is hereby granted, free of charge, to any person
    obtaining a copy of this software and associated documentation
    files (the "Software"), to deal in the Software without
    restriction, including without limitation the rights to use, copy,
    modify, merge, publish, distribute, sublicense, and/or sell copies
    of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.

Use
===

The package is intended as a one for one replacement for the built in
turtle module. Any existing turtle software that you have should work
just as before if you replace::

    from turtle import ...

with::

    from physicalturtle import ...

From that perspective, there is nothing much new to learn.

Examples
========

These examples can be run either by importing the run procedure or by
executing them from the command line::

  $python path/to/package/example_xxx.py

Using the command line is probably going to be appropriate if you have
downloaded the source and want to study how it works.

Random action
+++++++++++++

At the Python prompt::

   >>> from physical_turtle.example_random import run_me
   >>> run_me()

And watch the turtle bounce randomly around an enclosed space. 

Follow an Outline
+++++++++++++++++

At the Python prompt::

   >>> from physicalturtle.example_follow import 
   >>> run_me()

And watch the blue line work its way around the solid object.

A Constrained Random Walk
+++++++++++++++++++++++++

At the Python prompt::

   >>> from physicalturtle.example_walk import run_ahead, run_behind
   >>> run_ahead()
   >>> run_behind()

This example draws a random walk using a solid line, which means that
the turtle cannot cross its own trail.  The drawing rules mean that,
to achieve this, the turtle must switch between a solid line and a
not-solid line.  The example shows two ways to do this.


Change History
==============

Version 0.4
+++++++++++

Resolve 

    Issue #1: Solid lines are drawn even when pen is up

    Issue #2: Solid lines drawn using goto(x,y) are positioned wrongly.

    Issue #3: Follow an object outline losses contact with the object.

Version 0.3
+++++++++++

Start making changes for Python 3.  The Python 3 turtle module differs
slightly from the Python 2 version (see Python 3 documentation) and
these differences have been reflected in Physical Turtle.

Change the package name to `physicalturtle`.  This is more PEP8ish and
helps to keep some consistency with the PYPI package name.  My
apologies to current users for the inconvenience.  I realise it will
be inconvenient, but the hit now will save annoyance further down the
line.



Version 0.2
+++++++++++

The `touch_xxx` methods now work. This is illustrated in a new
example, `example_follow.py`.

The internal mechanism for finishing off the line clipping algorithm
has been tidied up.

The internal mechanisms now distinguish properly between the effective
size of the turtle, the safety_radius, as used in line clipping, and
the reach of the `touch_xxx` methods, the stick length.

Version 0.1
+++++++++++

An initial version focusing on the straight line geometry.