The Editors and Readers of COMPUTE!
Mixing Atari Graphics Modes
I own an Atari 1200XL computer. I've made a few BASIC programs of my own and I've been trying to get two graphics modes on the screen at the same time. For example, having GRAPHICS 1 at the top and GRAPHICS 2 at the bottom. Can you help?
James E. Sneed
A full explanation of modifying graphics modes is beyond the scope of this column, but try the following program. Set the variable G2 to the number of GRAPHICS 2 lines you'd like, then GOSUB 500. Lines 100-200 demonstrate the subroutine. This program modifies a GRAPHICS 1 display by POKEing in the display list bytes for GRAPHICS 2. You must not set G2 to less than 1 or greater than 11.
COMPUTE! has published several articles on this topic in back issues, some of which are no longer available. For more information, refer to "How to Design Custom Graphics Modes" in COMPUTE!'s First Book of Atari Graphics.
NO 100 G2=8:GOSUB 500
PI 110 FOR I=1 TO 24:? #6;"LINE ";I:N
FP 120 GOTO 120
MG 500 GRAPHICS 17:IF G2<1 OR G2>11 T
GI 510 DLIST=PEEK(560)+256*PEEK(561)
KG 520 FOR I=29-G2*2 TO 28-G2:POKE DL
EA 530 POKE DLIST+I,65:POKE DLIST+I+1
HJ 540 RETURN