From:	Moo-Juice <Ben AT flag DOT demon DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	0xB8000
Date:	Wed, 29 Jan 1997 10:28:11 +0000
Organization:	Honest Ron's Car Emporium
Distribution:	world
Message-ID:	<Ke0udLA7Yy7yEwJb@flag.demon.co.uk>
NNTP-Posting-Host:	flag.demon.co.uk
MIME-Version:	1.0
Lines:	63
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi all,

Some of you may remember the question I posted some days back,
concerning accessing the screen memory.  I decided that the easiest
method would be to to use nearptrs.  

#include <pc.h>
#include <sys/nearptr.h>

void CApp::BuffUpdate(CWin *WItem)
{

   int x;                        // Current X Position
   int y;                        // Current Y Position
   int c;                        // Counter
   int Len = WItem->Pos.w;       // Len of text to write

   POINT Query;
   Cov   Offender;

   MouseHide();
   if(__djgpp_nearptr_enable()==0) return;     // Enable near pointers
   char  *video = (char*)(__djgpp_conventional_base + 0xb8000);

   // Clip to Screen Width

   if(1-(WItem->Pos.x + Len) > (79))
        Len = (80 - WItem->Pos.x+1);

   for(y=WItem->Pos.y;y<=WItem->Pos.y+WItem->Pos.h-1;y++)
   {
      if(y>ScreenRows()-1) break;
      for(x=WItem->Pos.x;x<=WItem->Pos.x+Len-1;x++)
      {
         Query.x = x - WItem->Pos.x;
         Query.y = y - WItem->Pos.y;
         Offender = IsCoveredX(WItem,Query);
         if((Offender.Back==NULL) || (Ignore==TRUE))
         {
***         video[(y*160)+x] = WItem->Front[c];
            video[(y*160)+x+1] = WItem->Front[c+1];
         }
         else
         {
            Offender.Back[Offender.Pos] = WItem->Front[c];
            Offender.Back[Offender.Pos+1] = WItem->Front[c+1];
         };
         c+=2;
      };
   };
   MouseShow();

   __djgpp_nearptr_disable();   // Disable near pointers
};


It crashes on the line marked '***', with a signal error.

Can anybody shed any light on this problem?

-- 

Moo-Juice

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