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Section D:
D. The Graphics Interpreter
The Graphics Interpreter
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*
Graphics Interpreter
*
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As
you
know,
your computer can generate phantastic
colour
graphics.
These
graphics,
of course,
had to be included in EOS in some manner.
After
careful
considering
we
decided
to provide
for
two
ways
of
accessing graphics.
The first way is interesting for system programmers
and leads directly into the EOS kernel by EOS function 115.
This system
function
is discussed in detail in section C of the system
manual.
In
this section,
we will describe the other graphics facility which can be
used by every programmer.
At the beginning of the implementation there came the question of how it
would be possible to control graphics by every programming language.
To
avoid
the
necessity of linking assembly language subroutines
to
user
programs,
a
library of graphics functions (which,
in practice,
would
have
required several libraries for various programming languages)
was
precluded. The only remaining way was to use standard interfaces. Hence,
a
graphics language was developped which is invoked via the CRT
inter-
face.
Sending certain control sequences to the CRT driver activates the
graphics interpreter.
0.1. Activating the Graphics Interpreter
To start the graphics interpreter, there are three modes to select from:
1. Via
the
CRT
interface.
When you send
the
character
string
<ESCAPE>I
(uppercase I) to the CRT,
normal screen
display
is
switched
off.
All screen output is redirected to the
graphics
interpreter.
This
mode is termina-ted at the end of the program
run or by sending the graphics command "END".
2. By
the configuration program $DEVICE.
The graphics interpreter
is
installed
in the operating system as
the
physical
device
"GRAPH".
You
may assign this device firmly to the screen,
the
printer, or the auxiliary device. All output intended for one of
these devices is then processed by the graphics interpreter.
3. By
a special command of the SHELL command interpreter.
This is
more
some kind of game and primarily intended for
testing
the
graphics commands.
All command input beginning with an asterisk
"*" is passed directly to the graphics interpreter.
If you like
to,
you may interactively create some graphics. Of course, this
is not possible with the USRSHELL menu program.
EOS User's manual
Daeumling & Zimmermann
Page 103
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