

Article 1742 of sci.virtual-worlds:
Path: ultb!rit!rochester!udel!wupost!sdd.hp.com!spool.mu.edu!agate!bionet!raven.alaska.edu!milton!hlab
>From: [email-masked] (Frank van der Hulst)
Newsgroups: sci.virtual-worlds
Subject: Sega glasses & VGA (C source code)
Message-ID: <[email-masked]>
Date: 23 Sep 91 08:42:28 GMT
Sender: [email-masked] (Human Int. Technology Lab)
Organization: The Cave MegaBBS, Public Access Usenet, Wellington, NZ
Lines: 200
Approved: [email-masked]

Several people requested info on how to display 3D images, after my post of
the circuit to hook up Sega glasses to the PC. Following is source code to
do that.

Frank.

/*

VGA 320 * 400 * 256 * 2 frames routines.

Written by: F van der Hulst, 20/2/91

These routines display pixels in 320*400 mode by modifying the VGA
registers, as outlined in Programmer's Journal V7.1 (Jan/Feb '89)
article, pages 18-30, by Michael Abrash.

The advantage of 320 * 400, is that it gives two separate video pages,
which can be displayed on the screen independently. These can contain
two views of a scene, taken from slightly different viewpoints. These
are displayed alternately on the screen, in sync with a pair of
"chopper glasses", to give a 3D effect.
*/

#include <conio.h>

typedef unsigned char DacPalette[256][3];

/* Setvgapalette sets the entire 256 color palette     */
/* PalBuf contains RGB values for all 256 colors       */
/* R,G,B values range from 0 to 63                         */
/* Taken from SVGA256.H, by Jordan Hargraphix Software */

void setvgapalette(DacPalette *PalBuf)
{
  struct REGPACK reg;

  reg.r_ax = 0x1012;
  reg.r_bx = 0;
  reg.r_cx = 256;
  reg.r_es = FP_SEG(PalBuf);
  reg.r_dx = FP_OFF(PalBuf);
  intr(0x10,&reg);
}

unsigned int act_page = 0; /* Current page being written to */

#define VGA_SEGMENT        0xa000
#define SC_INDEX           0x3c4
#define GC_INDEX           0x3ce
#define CRTC_INDEX         0x3d4
#define DISPIO             0x3DA

#define MAP_MASK           2
#define MEMORY_MODE        4
#define GRAPHICS_MODE      5
#define MISCELLANEOUS      6
#define VRT_bit            8
#define MAX_SCAN_LINE      9
#define START_ADDRESS_HIGH 0x0c
#define UNDERLINE          0x14
#define MODE_CONTROL       0x17

void writepixel(int x, int y, unsigned char colour)
{
long addr;

        addr = ((x >> 2) + 320/4 * y + act_page);
        addr = ((addr & 0xffff0000l) << 4) + (addr & 0xffffL) + ((long) VGA_SEGM
ENT << 16);
        outport(SC_INDEX, (0x100 << (x & 3)) | MAP_MASK);
        *(char far*)addr = colour;
}

void set320x400mode(void)
{
struct REGPACK regs;
unsigned char x;

        regs.r_ax = 0x13;                               /* Set 320*200*256 graph
ics mode via BIOS */
        intr(0x10, &regs);

/* Change CPU addressing of video memory to linear (not odd/even, chain, or
        chain 4), to allow access to all 256K of display memory. Each byte will 
now
        control one pixel, with 4 adjacent pixels at any given address, one pixe
l
        per plane. */

        outportb(SC_INDEX, MEMORY_MODE);
        x = inportb(SC_INDEX+1);
        x &= 0xf7;                                                              
        /* Turn off chain 4  */
        x |= 4;                                                                 
        /* Turn off odd/even */
        outportb(SC_INDEX+1, x);
        outportb(GC_INDEX, GRAPHICS_MODE);
        x = inportb(GC_INDEX+1);
        x &= 0xef;                                                              
        /* Turn off odd/even */
        outportb(GC_INDEX+1, x);
        outportb(GC_INDEX, MISCELLANEOUS);
        x = inportb(GC_INDEX+1);
        x &= 0xfd;                                                              
        /* Turn off chain */
        outportb(GC_INDEX+1, x);

/* Now clear the whole screen, since the mode 13h set only clears 64K. Do this
        before switching CRTC out of mode 13h, so that we don't see grabage on t
he
        screen. */

        outport(SC_INDEX, 0x0f00 | MAP_MASK);                   /* Write to 4 pl
anes at once */
        setmem(MK_FP(VGA_SEGMENT, 0), 0xffff, 0);

/* Change mode to 320*400 by not scanning each line twice. */
        outportb(CRTC_INDEX, MAX_SCAN_LINE);
        x = inportb(CRTC_INDEX+1);
        x &= 0xe0;                                                              
/* Set maximum scan line to 0 */
        outportb(CRTC_INDEX+1, x);

/* Change CRTC scanning from doubleword to byte mode, allowing the CRTC to
        scan more than 64K */
        outportb(CRTC_INDEX, UNDERLINE);
        x = inportb(CRTC_INDEX+1);
        x &= 0xbf;                                      /* Turn off doubleword *
/
        outportb(CRTC_INDEX+1, x);
        outportb(CRTC_INDEX, MODE_CONTROL);
        x = inportb(CRTC_INDEX+1);
        x |= 0x40;                                      /* Turn on the byte mode
 bit, so memory is linear */
        outportb(CRTC_INDEX+1, x);
}

void end320x400mode(void)
{
struct REGPACK regs;

        regs.r_ax = 3;                          /* Return to text mode */
        intr(0x10, &regs);
}

/* Set visible page */

void setvispage(int page)
{
        outport(CRTC_INDEX, (page << 15) | START_ADDRESS_HIGH);
}

/* Set active page (page being written to */

void setactpage(int page)
{
        act_page = page ? 0x8000 : 0;
}

void WaitForVerticalRetrace(void)
{
static char chopper = 1;

        while (inportb(DISPIO) & VRT_bit) /* wait */ ;
        while ((inportb(DISPIO) & VRT_bit) == 0) /* wait */ ;
        if ((chopper++ & 1)== 0)                outportb(0x3fc, 1);
        else                                                                    
outportb(0x3fc, 3);
}

void main(int argc, char *argv[])
{
   set320x400mode();

/* Now fill the rgb_palette structure in memory with colour info */

   setvgapalette(&rgb_palette);

   setactpage(0);
/* Now call writepixel to put stuff on page 0 */
   setactpage(1);
/* Now call writepixel to put stuff on page 1 */

   while (!kbhit()) {
           WaitForVerticalRetrace();
           setvispage(0);
           WaitForVerticalRetrace();
           setvispage(1);
   }
   getch();
   end320x400mode();
}

-- 

Take a walk on the wild side, and I don't mean the Milford Track.
Kayaking: The art of appearing to want to go where your boat is taking you.

--
J. David Beutel  11011011  [email-masked]  "I am, therefore I am."