VGA Scroll

 BBS: Inland Empire Archive
Date: 03-31-93 (13:39)             Number: 332
From: EARL MONTGOMERY              Refer#: NONE
  To: FRED DISANO                   Recvd: NO  
Subj: VGA Scroll                     Conf: (2) Quik_Bas
Fred, here is the best I can up with at the moment.
This is the scroll for Screen 13 but there is a problem.
It is picking up garbage at the bottom. I use to know what
caused it and how to fix it but I can't retrieve it from my
old memory banks. If you change it to screen 7,9,10,11 or
12 the garbage disappears. Maybe you can figure it out or
someone will tell us how to fix it. Sorry about not having the
palette rotating routine ready for you but I am quite busy
with ASIC. Tell me exactly what you want to do with the
palettes. Palette rotating can have several different meanings.

SCREEN 13 'Change to screen 7,9,10,11,or 12 and the garbage
REM disappears.
FOR X = 1 TO 24
CIRCLE (160, 100), 90, 8
PAINT (161, 101), 12, 8
FOR I = 0 TO 16000 STEP 80
REM M stands for MSB.
M = FIX(I / 256)
OUT &H3D4, 12: OUT &H3D5, M
OUT &H3D4, 13: OUT &H3D5, I 'I know not poke a value over 255
                            'into a port but this doesn't
                            'cause any problems in this case.
WAIT &H3DA, 8 'Wait for vertical retrace
FOR D = 0 TO 2500: NEXT: 'Adjust for different scroll speed
FOR I = 16000 TO 0 STEP -80
M = FIX(I / 256)
OUT &H3D4, 12: OUT &H3D5, M
OUT &H3D4, 13: OUT &H3D5, I
WAIT &H3DA, 8: 'waits for vertical retrace
FOR DELAY = 0 TO 2500: NEXT: 'Adjust for different scroll speed
' That's it.
' Earl

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