From: csantill AT lausd DOT k12 DOT ca DOT us
Message-ID: <33C6ADCD.1B64@lausd.k12.ca.us>
Date: Fri, 11 Jul 1997 15:03:57 -0700
MIME-Version: 1.0
To: djgpp AT delorie DOT com
Subject: Bad FAQ suggestions
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from: csantill AT lausd DOT k12 DOT ca DOT us

I'm having problems try to access VGA mem.  I've looked it up in the FAQ
& Game Programming MegaSite.  I've gotten this code to compile(w/much
tinkering) but all I get is a blank screen & a stall.  Any help would be
much appreciated.  The code is attached here:

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#include <sys/nearptr.h>
#include <go32.h>
#include <dpmi.h>
#include <dos.h>
#include <time.h>

#define GRAPHICS        0x013
#define TEXT            0x03

/* Simple program to test speed of code - Only test how long it take
   to fill the screen 256 times(all colors)
     I'm expecting between 45-55 frames per sec
     I get about 40 frames per sec in TP 7   (286/16-Bit compiler)
     "  "    "   30   "     "   "  "  ASIC   (8086 compiler)
     "  "    "   25   "     "   "  "  QBASIC (Interpreted)
*/

// From Matt Reiferson's Game Programming Mega Site
char *video_buffer = (char *)0xA0000;

void Set_Video_Mode(int mode)
{
        __dpmi_regs r;

        r.x.ax = mode;
        __dpmi_int(0x10, &r);
}

// From Matt Reiferson's Game Programming Mega Site
void Plot_Pixel(int x, int y, char color)
{
   video_buffer[(y << 8) + (y << 6) + x] = color;
}

// From the FAQ - 18.4
void Set_Pixel(int x, int y, char c)
{
// Is the 0xA000 the correct segment to poke to?
  _farpokeb(_dos_ds, 0xA000*16+(y<<8)+(y<<6)+x, c);
}

void main(void)
{

// From the FAQ - 18.4 - Someone told me to initialize it in main
short video_memory = __dpmi_segment_to_descriptor(0xA000);

        int x,y,co;
        unsigned char c;
        uclock_t t[2][2];

        /* disable all memory protection */
        __djgpp_nearptr_enable();
        video_buffer += __djgpp_conventional_base;
        /* go to graphics mode */
        Set_Video_Mode(GRAPHICS);
        uclock();

        /* fill up the screen with random pixels */
        t[1][1]=uclock();
        for(co=0; co==510; co=co+2)
        {
          c=co/2; // <- Limit of char data type (DIV)
          for(y=0;y==199;y++)
            for(x=0;x==319;x++)
              Plot_Pixel(x,y,c);
        }
        t[1][2]=uclock();

        // Now do it like the FAQ
        t[2][1]=uclock();
        for(co=0; co==510; co=co+2)
        {
          c=co/2; // <- Limit of char data type (DIV)
          for(y=0;y==199;y++)
            for(x=0;x==319;x++)
              Set_Pixel(x,y,c);
        }
        t[2][2]=uclock();



        /* go back to text mode */
        Set_Video_Mode(TEXT);

        /* reenable memory protection */
        __djgpp_nearptr_disable();


        // I'm not sure these 2 line are correct
        printf("1. Reiferson fps = %i\n",
                 ((t[1][2]-t[1][1])/CLOCKS_PER_SEC)/256);
        printf("2. FAQ fps = %i\n",
                 ((t[2][2]-t[2][1])/CLOCKS_PER_SEC)/256);
        exit(0);
}

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