32-bit Video DAC

Dec 16, 2001

Imran Haider

Dec 17, 2001

Walter

Dec 18, 2001

Oct 23, 2006

Dec 18, 2001

Feb 20, 2002

Hi. I was wondering that if you set the video mode to a 32-bit mode (such as 640x480 in 32-bit color mode), where does the color DAC stay? I mean, in 256 color mode, it is reasonable for the video card to store 768 (256 * 3) byte of color data. In 32-bit mode, there are over a billion colors, where do they all stay?

The best book I've seen on programming graphics cards is the ZEN book: www.digitalmars.com/bibiliography.html "Imran Haider" <absolute1008@hotmail.com> wrote in message news:9vjc4d$2ob7$1@digitaldaemon.com... Hi. I was wondering that if you set the video mode to a 32-bit mode (such as 640x480 in 32-bit color mode), where does the color DAC stay? I mean, in 256 color mode, it is reasonable for the video card to store 768 (256 * 3) byte of color data. In 32-bit mode, there are over a billion colors, where do they all stay?

Imran Haider a écrit : > Hi. I was wondering that if you set the video mode to a 32-bit mode (such as 640x480 in 32-bit color mode), where does the color DAC stay? I mean, in 256 color mode, it is reasonable for the video card to store 768 (256 * 3) byte of color data. In 32-bit mode, there are over a billion colors, where do they all stay? I never tried to program for 32 bit color, even 16 bit. VBE int 10h fc 4f01h can give you informations about video memory organisation. Roland

> Imran Haider a écrit : > > Hi. I was wondering that if you set the video mode to a 32-bit mode (such as 640x480 in 32-bit color mode), where does the color DAC stay? I mean, in 256 color mode, it is reasonable for the video card to store 768 (256 * 3) byte of color data. In 32-bit mode, there are over a billion colors, where do they all stay? Isn't it 24 bit color ? As told before never programmed for such modes. My bet is: There is 3 planes of 8 bit/pixel, one for red, one for green, one for blue. You switch from one plane to the other the same way as for 16 color ega/vga 1 bit/pixel planes modes. But it is just a bet.. Roland

February 20, 2002

Re: 32-bit Video DAC

Posted by Trevor Johns
in reply to Imran Haider

Permalink

Trevor Johns

Posted in reply to Imran Haider

Permalink

Imran Haider wrote:

> Hi.  I was wondering that if you set the video mode to a 32-bit mode (such as 640x480 in 32-bit color mode), where does the color DAC stay? I mean, in 256 color mode, it is reasonable for the video card to store 768 (256 * 3) byte of color data. In 32-bit mode, there are over a billion colors, where do they all stay?
> 

In HiColor & TrueColor modes each and every pixel holds it's own RGB value (3*5 bits per channel+spare bit=15-bit HiColor or use 6 bits for Green [the eye is more sensitive to green] for 16-bit HiColor; 8 bits per channel giving 24-bit color, then add a spare byte for 32-bit color [fits better into registers is all]). Since each pixel determines it's own exact color, you don't need any DAC to do color conversion as in palettized modes (what shade of purple is color number 7???)

Here's some sample DOS code I wrote a while ago that should give you a start (requires a VESA driver - most video cards now come with it built into the BIOS or as a DOS TRS driver to load)

VESA.H
======
/*
 * VESA.H - SuperVGA VESA Interface Routines
 */

#if !defined(VESA_H)

#define VESA_H

struct VESAInfo {
	char VESASignature[4];				/* "VESA" */
	unsigned VESAVersion;
	char far * OEMString;
	unsigned char VESACapabilities[4];
	unsigned far * VESAModePtr; 		/* ptr to mode numbers, -1 terminated */
    unsigned MemorySize;                /* # of 64K pages (VESA 1.2) */
    char reserved[236];
};

struct VESAMode {
	unsigned ModeAttributes;
/*
	0000 0001	mode supported in hardware
	0000 0010	Extended mode information available
	0000 0100	Output functions supported by BIOS
	0000 1000	Color mode (0=mono)
	0001 0000	Graphics mode (0=text mode)
*/
    unsigned char WinAAttributes;
	unsigned char WinBAttributes;
/*
	0000 0001	Window is supported
	0000 0010	Window is readable
	0000 0100	Window is writable
*/
	unsigned WinGranularity;			/* in K bytes */
	unsigned WinSize;					/* in K bytes */
	unsigned WinASegment;				/* window A segment address */
	unsigned WinBSegment;				/* window A segment address */
	void (far * WinFuncPtr)(void);
	unsigned BytesPerLine;				/* logical scanline length */

/* optional extended info */
	unsigned XResolution;
	unsigned YResolution;
	unsigned char XCharSize;
	unsigned char YCharSize;
	unsigned char Planes;
	unsigned char BitsPerPixel;
	unsigned char Banks;
	unsigned char MemoryModel;
/*
	00h = Text mode
	01h = CGA graphics
	02h = Hercules graphics
	03h = 4-plane planar (EGA)
	04h = Packed pixel
	05h = Non-chain 4, 256 color
	06h = Direct Color (HiColor [15/16 bit] or TrueColor [24/32 bit])
	07h = YUV (Luminance/Chrominance)
	08h-0Fh = Reserved, to be defined by VESA
	10h-FFh = To be defined by OEM
*/
    unsigned char BankSize;             /* bank size in K */
	unsigned char NumPages;
	unsigned char Reserved;
	unsigned char RedMask;
	unsigned char RedShift;
	unsigned char GreenMask;
	unsigned char GreenShift;
	unsigned char BlueMask;
	unsigned char BlueShift;
	unsigned char ReservedMask;
	unsigned char ReservedShift;
	unsigned char DirectColorInfo;
	char reserved[217];
};

int isVESA(void);
int VESAMode(unsigned mode);
void VESAPoint(unsigned x, unsigned y, long color);
long VESARGB(unsigned char r, unsigned char g, unsigned char b);
void VESAPallette(unsigned char *pal);

enum VESAModes { V640x400x256 = 0x100,
				 V640x480x256,
				 V800x600x16,
				 V800x600x256,
				 V1024x768x16,
				 V1024x768x256,
				 V1280x1024x16,
				 V1280x1024x256,
				 V80x60,
				 V132x25,
				 V132x43,
				 V132x50,
				 V132x60,
				 V320x200x32K,
				 V320x200x64K,
				 V320x200x16M,
				 V640x480x32K,
				 V640x480x64K,
				 V640x480x16M,
				 V800x600x32K,
				 V800x600x64K,
				 V800x600x16M,
				 V1024x768x32K,
				 V1024x768x64K,
				 V1024x768x16M,
				 V1280x1024x32K,
				 V1280x1024x64K,
				 V1280x1024x16M
               };

#endif


VESA.C
======
/*
 * VESA.C - SuperVGA VESA Interface Routines
 */

#include "vesa.h"
#include <dos.h>
#include <limits.h>

struct VESAInfo vinfo;
struct VESAMode vmode;
static unsigned vesapage;

int isVESA(void)
{
struct VESAInfo far *fp = &vinfo;
union REGS reg;
struct SREGS sreg;

	reg.x.ax = 0x4f00;
	sreg.es = FP_SEG(fp);
	reg.x.di = FP_OFF(fp);
	return (int86x(0x10, &reg, &reg, &sreg) == 0x004f);
}

int VESAMode(unsigned mode)
{
union REGS reg;
struct SREGS sreg;
struct VESAMode far *fp = &vmode;

	vesapage = 0xffff;
	if (mode < 0x100) {
		reg.x.ax = mode;
		int86(0x10, &reg, &reg);
		if (mode == 0x13) { /* MCGA graphics */
			vmode.ModeAttributes = 0x1f;
			vmode.WinAAttributes = 0x07;
			vmode.WinBAttributes = 0x00;
			vmode.WinGranularity = 64;
			vmode.WinSize = 64;
			vmode.WinASegment = 0xa000;
			vmode.WinBSegment = 0;
			vmode.BytesPerLine = 320;
			vmode.XResolution = 320;
			vmode.YResolution = 200;
			vmode.XCharSize = 8;
			vmode.YCharSize = 8;
			vmode.Planes = 1;
			vmode.BitsPerPixel = 8;
			vmode.Banks = 1;
			vmode.MemoryModel = 4;
			vmode.BankSize = 0;
			vesapage = 0;
		}
		return (1);
	} else {
		reg.x.ax = 0x4f01; /* get VESA mode info */
		reg.x.cx = mode;
		sreg.es = FP_SEG(fp);
		reg.x.di = FP_OFF(fp);
		if (int86x(0x10, &reg, &reg, &sreg) != 0x004f ||
			(vmode.ModeAttributes & 0x0001) == 0) /* mode not supported */
			return (0);
		reg.x.ax = 0x4f02;
		reg.x.bx = mode;
		return (int86x(0x10, &reg, &reg, &sreg) == 0x004f);
	}
}

/*
 * Note: VESAPoint should work in all 256/32K/64K/16M color modes
 */

void VESAPoint(unsigned x, unsigned y, long color)
{
union REGS reg;
struct SREGS sreg;
unsigned long addr;
unsigned char far *fp;
unsigned pageno, offset;

	addr = (long)y * vmode.BytesPerLine + x * (vmode.BitsPerPixel/9+1);
	pageno = (unsigned)(addr / ((long)vmode.WinGranularity << 10));
	offset = (unsigned)(addr % ((long)vmode.WinGranularity << 10));
	if (pageno != vesapage) {
		reg.x.ax = 0x4f05;
		reg.x.bx = 0x0000; /* select bank, window A */
		reg.x.dx = vesapage = pageno;
		int86x(0x10, &reg, &reg, &sreg);
	}
	fp = (unsigned char far *)(((long)vmode.WinASegment << 16) + offset);
	if (vmode.BitsPerPixel == 8)
		*fp = (unsigned char)color;
    else if (vmode.BitsPerPixel == 15 || vmode.BitsPerPixel == 16)
		*((unsigned far *)fp) = (unsigned) color;
    else if (vmode.BitsPerPixel == 24 || vmode.BitsPerPixel == 32) {
        *fp++ = (unsigned char) (color & 0xff);         /* red */
        *fp++ = (unsigned char) ((color >> 8) & 0xff);  /* green */
        *fp = (unsigned char) ((color >> 16) & 0xff);   /* blue */
    }
}

long VESARGB(unsigned char r, unsigned char g, unsigned char b)
{
long rl, gl, bl;

    rl = r >> (CHAR_BIT - vmode.RedMask);
    gl = g >> (CHAR_BIT - vmode.GreenMask);
    bl = b >> (CHAR_BIT - vmode.BlueMask);
    return (rl << vmode.RedShift) | (gl << vmode.GreenShift) | (bl << vmode.BlueShift);
}

void VESAPallette(unsigned char *pal)
{
union REGS reg;
struct SREGS sreg;
char far *fp = (char far *) pal;

	reg.x.ax = 0x1012;
	reg.x.bx = 0;		/* starting pallette entry */
	reg.x.cx = 256;
	sreg.es = FP_SEG(fp);
	reg.x.dx = FP_OFF(fp);
	int86x(0x10, &reg, &reg, &sreg);
}


ZZ3.C
=====
/*
 * VESA graphics
 */

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#include <dos.h>
#include <limits.h>

#include "vesa.h"

extern struct VESAInfo vinfo;
extern struct VESAMode vmode;


void main(int argc, char *argv[])
{
int x, y;

	if (!isVESA()) {
		fprintf(stderr, "VESA not installed\n");
		exit(1);
	}
    if (!VESAMode(V800x600x32K)) {
        fprintf(stderr, "Mode not supported\n");
		exit(1);
	}
    for (y = 172; y < 428; y++) {
        /* left */
        for (x = 0; x < 256; x++)
            VESAPoint(x, y, VESARGB(x, y-172, 0));      /* RED-GREEN */
        /* middle */
        for (x = 272; x < 528; x++)
            VESAPoint(x, y, VESARGB(0, x-272, y-172));  /* GREEN-BLUE */
        /* right */
        for (x = 544; x < 800; x++)
            VESAPoint(x, y, VESARGB(y-172, 0, x-544));  /* BLUE-RED */
    }
    cprintf("\a");
    getch();
	VESAMode(3);
	exit(0);
}

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