From: "Alex Barsamian" <bigalex AT worldnet DOT att DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Yet another graphics problem...
Date: Sun, 5 Oct 1997 01:28:48 -0600
Organization: Biohazard Software
Lines: 342
Message-ID: <617g3k$ipr@bgtnsc03.worldnet.att.net>
NNTP-Posting-Host: 12.65.147.223
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Precedence: bulk

 I started out tonite porting my crusty mode 13h real mode graphics code out
to djgpp.  I can init the graphics mode okay, even write to the screen
without too much trouble.  Now for some reason when I began to implement the
double buffer routines into the new source file, I compile without any
trouble, but about 1/4 of the time, when I should be seeing a PCX image, I
see a blank screen (in graphics mode), and the rest of the time I get a
lovely page fault.  The source code from tonite's work follows.  It's just a
series of simple, non-portable (yet!) functions to muck around in graphics,
yet I am confounded as to why it is not working as it should.  Any
suggestions? (besides getting Allegro, which I do have, and think is
wonderful, but I just want to write this code by myself for the most part,
for the experience benefit :-)   I think we can all understand that, huh?)
Thanks in advance.  Please email as well as post, I may not be able to read
the newsgroups for a bit and I'd hate to muck thru bluesnews to find the
responses :-) )

regards,
alex

djvbepcx.c follows (the source is also attached in case the horribleness
that is IE4 screws up the formatting):

#include <stdio.h>
#include <stdlib.h>
#include <dpmi.h>
#include <sys/nearptr.h>

int c, width, height, bytes_per_line, i;
char ch;
unsigned char *videoptr = (unsigned char *)0xA0000;
unsigned char pallete[768];
unsigned char *buffer;

// switch vesa banks using int10

void VBE_SwitchBank(short bank) {
 __asm__ __volatile__("
  movw $0x4F05, %%ax;
  xorw %%bx, %%bx;
  int $0x10"
  : : "d" (bank) : "ax", "bx", "dx"
 );
}

// set a vbe mode

void VBE_SetMode(unsigned short mode) {
 __dpmi_regs regs;
 regs.x.ax = 0x4F02;
 regs.x.bx = mode;
 __dpmi_int(0x10, &regs);
}

// goto textmode

void VBE_Shutdown() {
 VBE_SetMode(0x0003);  // set to text mode
}

// Blit a buffer (unsigned char *) onscreen, switching
// banks no more than absolutely neccesary.
// this assumes the vbe 1.2 are present and functioning correctly, that is
// to say, all banks look like they are 64k whether they physically are or
// not

void copy_buffer()

        char *source;
        char *dest;
        source=buffer;
 dest = videoptr + __djgpp_conventional_base;
 __djgpp_nearptr_enable();
     /* 640*480*8bpp = 307200 bytes = 4*64K + 45056 bytes */
        VBE_SwitchBank(0);              // start at bank 0
        memcpy(dest, source, 65536L);   // copy 64k
        VBE_SwitchBank(1);              // switch to bank 1
        source += 65536L;               // copy 64k
        memcpy(dest, source, 65536L);   // rinse, lather, repeat . . . .
 VBE_SwitchBank(2);
        source += 65536L;
        memcpy(dest, source, 65536L);
 VBE_SwitchBank(3);
        source += 65536L;
        memcpy(dest, source, 65536L);
 VBE_SwitchBank(4);
        source += 65536L;
        memcpy(dest, source, 45056L);   // only 45056 because
640*480!=65536*5
        __djgpp_nearptr_disable();
}

// get a pcx, skipping most unnecessary stuff that can be assumed
// e.g., size (for now 640x480 pcx's are all i'll use, 8 bpp, etc.
// I know this is far from portable but this is just to get this thing
// rolling

unsigned char *load_pcx(char *filename)
{
        FILE *f;                        // file handle
        int count, c;                   // loop vars
        unsigned char data;             // current data
        int num_bytes;                  // number of bytes in RLE run
        unsigned char *b;               // buffer
        f = fopen(filename, "r");
        if (!f) {
                printf("file not found\n");
  return NULL;
                }

 getc(f);                    /* skip manufacturer ID */
 getc(f);                    /* skip version flag */
 getc(f);                    /* skip encoding flag */
        getc(f);

        width = -(getw(f));        /* xmin */
        height = -(getw(f));       /* ymin */
        width += getw(f) + 1;      /* xmax */
        height += getw(f) + 1;     /* ymax */

        b = malloc(width*height);  // malloc an appropriate buffer

        getc(f);                   /* skip DPI values */

        for (c=0; c<16; c++) {           /* skip the 16 color pallete */
                getc(f);                 /* originally intended on using it
*/
                getc(f);                 /* (for some reason . . . )  */
                getc(f);                 /* which is why it looks like this
*/
 }

        getc(f);                    // skip junk

        getc(f);

        bytes_per_line = getw(f);   // just in case i start to use double-
                                    // scripted buffers

 for (c=0; c<60; c++)             /* skip some more junk */
  getc(f);

        count=0;
        while(count<=(width*height)) {
  // grab first piece of RLE data
                data=getc(f);
  // is it RLE?
  if((data>=192) && (data<=255)) {
   // if it is, how long is the run?
   num_bytes=data-192;
   // now that we know how long it is, grab the data
                        // for the actual run.
                        data=getc(f);

   // plug (data) into the buffer (num_bytes) times
   while(num_bytes-->0)
                                b[count++]=data;

  } // end if RLE
 // not RLE?
 else
  // plug it in to the buffer
                b[count++]=data;
       }


 while (!feof(f)) {          /* look for a 256 color pallete */
  if (getc(f)==12) {
  for (c=0; c<256; c++) {
                        pallete[c]   = getc(f) / 4; // load it in
   pallete[c*2] = getc(f) / 4;
   pallete[c*3] = getc(f) / 4;
   }
 break;
 }
}

 fclose(f);
        return b;
}


void VBE_Pal(unsigned char ColorNo, unsigned char R,
      unsigned char G,       unsigned char B) {

 outp (0x03C8,ColorNo); // here is the pallette color I want to set
        outp (0x03C9,R);       // set r,
        outp (0x03C9,G);       // g,
        outp (0x03C9,B);       // and b compo appropriately

}

void main()

        VBE_SetMode(0x101);             // fire up graphics to 0x101
        buffer=load_pcx("picture.pcx");
        if(*buffer==NULL) {             // do we have our picture?
                VBE_Shutdown();
                printf("error loading pcx");
                exit(0);
                }

        for(i=0; i<256; ++i)            // set the pallete appropriately
              VBE_Pal(i, pallete[i], pallete[i*2], pallete[i*3]);

        copy_buffer();                  // put the buffer onscreen
        getch();
        VBE_Shutdown();
}






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