From: NoEmailAds AT execpc DOT com (Chris Giese)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: VGA DAC programming
Date: Mon, 13 Jan 2003 03:39:42 GMT
Organization: PROPULSION GROUP
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

"Joel_S" <jbs30000 DOT news DOT invalid AT web2news DOT net> wrote:

>Well, since I'm writting routines for screen mode 0x12 being able to
>change the palettes of the 16 colors is necessary for properly diplaying
>a bitmap file.  But I'm not to worried, the built in SCREEN commands in

The 16 colors are processed by both the 256-color palette (the DAC)
and the 16-color palette in the first 16 registers of the Attribute
Controller. You can set the palette with code like this:

	int i, j;

	for(i = 0; i < 16; i++) {
/* reset Attribute Controller (AC) flip-flop so 0x3C0 is AC address */
		(void)inportb(0x3DA);
/* set AC address = i. You must clear bit b5 here to modify the palettes.
Clearing this bit will also blank the display. */
		outportb(0x3C0, i);
/* read AC register #i
THIS is the index into the 256-color palette, not 'i' */
		j = inportb(0x3C1);
/* set the 256-color palette (DAC) entry. Only the bottom 6 bits of each
R, G, and B entry are significant, so we divide by 4. Change RED, GREEN,
and BLUE to whatever is appropriate for your code. */
		outportb(0x3C8, j);
		outportb(0x3C9, RED  [i] / 4);
		outportb(0x3C9, GREEN[i] / 4);
		outportb(0x3C9, BLUE [i] / 4);
	}
/* set bit b5 in AC address register to lock palette and unblank display */
	(void)inportb(0x3DA);
	outportb(0x3C0, 0x20);