Displaying Graphics On The Screen - Commodore 128 System Manual

a 9K area for your bit-mapped screen information. 8K is reserved
for the data for your bit map and the additional 1K is dedicated for
the color data (video matrix). Since 9K is a substantial block of
memory, you may want to use it again for another purpose later
on in your program. This is the purpose of CLR. It reorganizes the
Commodore 128 memory and gives you back the 9K of memory
that was dedicated to the bit map-screen, so you can use it for
other purposes.
The format for CLR is as follows:
GRAPHIC CLR
When using this format, omit all other GRAPHIC command
parameters.
Add the following command to your program. It places the C128
in standard bit-map mode and allocates an 8K bit-map screen
(and 1K of color data) for you to create graphics.
40 GRAPHIC 1,1
The second 1 in this command clears the bit map screen. If you
do not want to clear the screen, change the second 1 to 0 (or
omit it completely).
NOTE: If you are in bit-map mode and are unable to return
to the text screen, press the RUN/STOP and RESTORE
keys at the same time, or press the ESC key followed by X,
to return to the 80-column screen. Even though you can only
display graphics with the VIC (40 column) chip, you can still
write graphics programs in 80-column format. If you have
the Commodore 1901 dual monitor and you want to view
your graphics program while it is running, you must select
the 40-column output by switching the slide switch on the
monitor to 40-column output.

Displaying Graphics on the Screen

So far, you have selected a graphics mode and the colors you
want. Now you can start displaying graphics on the screen. Start
with a circle.
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