Instruction manual
The ploting vector string is then broken
up
into
groups
of
two or three, each
group (confusion!) reading from right
to
left. To add a
little
more danger
to
the
game, the rules require that no group
of
vectors may end with a move-up vector
or with a plot-then-move vector, in which
case the group will contain at most
two
plotting vectors. The table in Figure
3a
shows how the above string is subdivid-
ed.
In
this case, because of the restric-
tions on termination, each group can
contain only
two
vectors. The rules for
formulating these vectors groups are ac-
tually quite soundly based, as will
become clear in later considerations.
We are not done yet. In the next
step, each plotting vector as
it
appears
in the table in Figure
3a
is replaced by a
3-bit (octal) code. The code is shown in
Figure
4,
along
with
the decimal
equivalents. Note that the decimal code
for a plot-then-move vector is obtained
simply
by
adding decimal 4
to
the cor-
responding move-only vector. There
is
a
certain amount
of
method in
this
madness. The 3-bit code translation for
the plotting vectors in Figure
4,
which
represent our shape, is displayed in
Figure
3b.
The next opportunity for confusion
(and error) appears now, when the bit-
strings in Figure 3b are re-grouped and
assembled
into
nybbles (Figure 3c) and
the nybbles are each translated
into
hex-
idecimal numbers (Figure
3d).
The pairs
of hexidecimal numbers,
of
course,
represent the content
of
one byte. This
is the byte that is stored in the shape
table. In essence, then, the shape table
is a list of hexidecimal numbers, which,
after translation into binary and
re-
grouping, represents the collection
of
3-bit codes equivalent to the
plotting
vectors, which in turn represent the
original shape.
In
the parlance
of
mathematics, the shape has been map-
ped
onto the set
of
hexidecimal
numbers.
If by now the reader is feeling a
tingle of impatience with
this
descrip-
tion, multiply
that
feeling by a factor
of
at least ten, and you will
be
on the verge
of understanding what it feels like
to
carry out these steps. To add
to
the
frustration, there are enough booby
traps laid by APPLE to ensure
quite
a de-
cent probability
that
after
you have gone
through this travail, the shape that final-
ly appears on your screen will be
misshapen. With a computer at hand, it
seems silly to
be
bogged down by a pro-
cess like
this-and
that's
what the rest
of
this article is about: a computer pro-
gram in APPLESOFT BASIC
that
allows
easy graphic:
input
of
a shape or
character with automatic generation
and
storage
of
a
correct
shape
table-graphics
without
tears, so
to
speak.
._.
",
-_
..
_.-
.,
,---~""--
.~==~.-=~":'~=~~-
..::-
--~.:.::..
..
~
.•
..:.=-=--=--.-=-:
'
..
__
_
:.
':c
....
:_
__
.. .
..
--~
---
'-
....
-
..
- -_._.
---'-.
--~.
~
.---'----'--
.
~-.~.:::==__~
__
::=~._:.-_i
•.
~
.
-==.:~t:=.
-=-_=
._:
-
---+
_..:..--;--:
-;.-
--
-_
..
~:-
-~.--t-~
..
-
.
--~-
--
..
-
--
-~-
.-'---.,
-,
.
;.'-,
-
=-:'»:.
=--':-_:~~':::.''=:
_-:=~
t-
..:~;-==:_
..
~
~-~=~-=-
::~~~~~;E?~+
--
---
-_
..
--
_..,
._~_._--
.:::--:
•.
=:
~=--.
-
--~=.:±~
.~~
.=-~_:~
Figure 1: Shape
to
be coded
Fig. 2: Layout
of
Plotting Vectors.
(S)
is
the starting point. With
this choice
of
(S),
the shape will
be
lower right
justified
and will
plot
with
one empty column
to
the right
of
the shape.