320x200x16???? on cga 1/2

 BBS: Inland Empire Archive
Date: 08-02-92 (11:56)             Number: 185
From: MATT PRITCHARD @ 930/21      Refer#: NONE
  To: JIM CALES                     Recvd: NO  
Subj: 320x200x16???? on cga 1/2      Conf: (1) 80xxx

IZ>  There's always the trick of changing palettes every time the monitor's
IZ>moves to a new line. A friend of mine used this trick to get a 320x200x16
IZ>mode with a CGA adapter.

JC>This information on the multi color CGA stuff is getting my curiosity
JC>going.  Could you elaborate on this process or perhaps provide a small
JC>snippet of code?  Thanks.     Jim

No, actually the CGA is capable of 160x100x16 colors directly.. a Graphics
mode that IBM should have included in their BIOS (they did
have it the PCjr)... Here is some code in BASIC for setting
it.

Credit goes to the Origional author, Lawrence McCaplin

Since the code just sets registers, plots points, etc, and
lets you use another undocumented graphics mdoe, I think
people shouldn't be too mad about it...

Also, on my ATI VGA-Wonder XL, I have to run a Batch file
to set up the VGA card so it can properly emulate this
mode...

============================ CGA-16.BAS ==========================

DEFINT A-Z

DECLARE SUB ScreenMode160 (Mode%)
DECLARE SUB ClearScreen (Mode%, DrawColor%, NoClear%)
DECLARE SUB ExitMode () DECLARE SUB DrawDot (x%, y%,
DrawColor%) DECLARE SUB DrawLine (x1%, y1%, x2%, y2%,
DrawColor%) DECLARE SUB GetInput () DECLARE SUB Pause ()

RANDOMIZE TIMER

'       SuperCGA version 1.0
'       Color Graphics Adapter Enhancement Routines '
Tesseract Productions '

'   BEGIN (main)

SCREEN 0, 0, 0: WIDTH 80

PRINT "Super CGA"
PRINT "Version 1.0"
PRINT "Tesseract Productions"
PRINT "Programmed by Lawrence McAlpin"
PRINT ""
PRINT "Demonstration program on the 160x100 128-color capabilities of the
CGA" PRINT "monitor.  Tested on an AT&T PC 6300 with built-
in AT&T CGA and a" PRINT "Verxion 386 with BOCA SuperVGA."
PRINT PRINT "WARNING! This program may not work properly on
emulated CGA sreen" PRINT "modes (i.e., it may not work right on EGA, VGA,
MCGA, or XGA cards.)" PRINT "The author assumes no
liability for any damag that may result from" PRINT "the
use of this program.  If you try this program out you are"
PRINT "responsible for anything that may occur." PRINT
PRINT "128 Color CGA Demonstration Program" PRINT PRINT
"Hit '+' or '-' to change the 'background'" PRINT "Hit 'L'
or 'l' to draw random dots and lines" PRINT "Hit 'M' or 'm'
to change between box and fuzzy modes" PRINT "Hit 'Q' or
'q' to quit" PRINT "PRESS ANY KEY TO CONTINUE" Pause

ScreenMode160 1
ClearScreen 1, 0, 0
DrawLine 0, 1, 79, 1, 3
DrawLine 0, 1, 0, 79, 3
DrawLine 3, 1, 40, 80, 4


'   demonstrate the first 128 colors

FOR counter = 0 TO 79
    DrawDot counter, 15, counter
NEXT counter
FOR counter = 80 TO 127
    DrawDot counter - 80, 20, counter
NEXT counter

GetInput

'   Pause

'   there are two types of screen 'modes' '   they are box
and fuzz, ScreenMode160 and ClearScreen take the mode '
parameter for box as zero, and fuzz for anything else '
fuzz mode smooths the box-graphics so they don't look AS
boxy as they '   really are

ClearScreen 1, 0, 0

'   this returns you to the regular 320x200 CGA 4-color mode '   if you
neglect to ExitMode then you will find your screen display
'   acting extremely strangely as the registers won't be
restored to '   something normal

ExitMode

'   END (main)

END




SUB DrawDot (x, y, DrawColor)

 '  check for out of bounds errors

 IF DrawColor < 0 OR DrawColor > 255 THEN EXIT SUB
 IF x < 0 OR x > 79 THEN EXIT SUB
 IF y < 0 OR y > 99 THEN EXIT SUB

 a = ((2 * x + (y * 160)) AND &HFFFE) + 1
 n = PEEK(a)
 POKE a, (n AND &HF0) OR DrawColor

END SUB

DEFINT A-Z
SUB DrawLine (x1, y1, x2, y2, DrawColor)

IF ABS(x1 - x2) > ABS(y1 - y2) THEN
    IF x1 > x2 THEN
        SWAP x1, x2
        SWAP y1, y2
    END IF
    dx = (x2 - x1)
    dy = (y2 - y1)
    IF dx <> 0 THEN
        b! = dy / dx
    ELSE
        b! = 0
    END IF
    m! = y1 - x1 * b!
    FOR x = x1 TO x2
        IF b! <> 0 THEN
            y = INT(m! + x * b!) + .5
        ELSE
            y = y1
>>> Continued to next message
===
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