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Section D:
0.2. Instruction Format
The Graphics Interpreter
*******************************
*
Graphics Interpreter
*
*******************************
Each graphics instruction consists of a normal line of text,
terminated
by a <CR><LF> control character pair.
This means that you can
generate
these instructions by ordinary output statements from within your appli-
cation program.
Each line begins with a graphics instruction code writ-
ten in plain text, most of them being three or four characters long. The
character
mode is of no concern,
as the interpreter will accept upper-
case as well as lowercase characters.
The instruction code is
followed
by parameters,
if the specific command requires any. The parameters are
separated
by commas.
Space characters may be interspersed freely
any-
w~ere
in
the instruction line (of course,
not within the
instruction
code or a parameter itself).
Each
parameter has certain limits.
If these bounds are
exceeded,
the
maximum possible value is substituted in most cases. The limits are:
X-axis
Y-axis
Colour
Bit. images
0
to
639
0
to
399
0
to
7
Ql
to
126
If you omit one or more parameters, they are substituted by zero values.
So
do not be surprised to see nothing on the screen when you
accident-
ially
forget to specify the colour,
thus "plotting" black (colour
=
0)
on a black screen!
Let
1
s
have
a look at the parameters:
Graphics are located in the
so-
called second quadrant. This means that the coordinate point (0,0), also
called the "origin",
is located in the upper left corner of the screen:
From here,
the x-axis runs
to the right edge of the
screen,
whereas
the y-axis runs to the bottom.
A
line consists of a multiple of
16
image
dots or
11
pixels
11
•
Normally·,
these form a continuous line.
But you may
redefine
the line mode by the graphics instruction
11
MASK
11
,
so that you
can also generate dotted or dashed lines.
There
are eight different colours available.
The list below shows
you
the
colours
and their corresponding codes which have to
be
specified
with a number of instructions:
0 -
black
1 -
blue
2 -
red
3 -
magenta
4 - green
5 -
6
cyan
y-ellow
- white
7
All other values will be substituted by 7
white.
EOS User
1
s manual
Daeumling & Zimmermann
Page 104
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