I have been doing some full screen graphics programming lately and can not
seem to get VioGetPhysBuf to work.  I expected it to be the easiest part,
but it eludes me even though all the 'tough' parts are working flawlessly. 
I have used it before under 2.1 but I do not have my code from then to use
as a reference anymore.  I am starting to suspect a change in Warp or
VisualAge versus 2.1 and CSet++ 2.0.  The idea is to get a basic graphics
system working and then compare the performance difference versus DIVE in
order to decide if it warrants the development of seperate graphics code
for multiple video cards.

The problem is that when I attempt to write to the address defined by the
pointer returned from the function GetPhysBuf below I get a memory
violation.  The only similar source code I could find was in the EMX SVGA
libararies for OS/2 and the code was essentially no different from mine.

Here's a version of it that has been stripped down to a simple attempt to
put one character on the text screen using the direct buffer access.  The
error checking is overkill until I can find why this fails, so the
assertions, logging and VioScr(Un)Lock can be removed to really strip this
down.
 
#define INCL_NOPMAPI
#define INCL_NODOS
#define INCL_VIO
#include 
#include 
#include 
#include "log.h"

HLOG hlLog;

PBYTE GetPhysBuf(void)
{
  VIOMODEINFO vmi;
  VIOPHYSBUF  vpb;
  PBYTE result;
  APIRET rc;

  vmi.cb = sizeof(VIOMODEINFO);
  assert(!(rc=VioGetMode(&vmi, 0)));
  logEntry(hlLog, TRACE, "vmi.buf_addr : %p", vmi.buf_addr);
  logEntry(hlLog, TRACE, "vmi.buf_length : %lu", vmi.buf_length);
  logEntry(hlLog, TRACE, "vmi.full_length : %lu", vmi.full_length);
  vpb.pBuf = (PBYTE) vmi.buf_addr;
  vpb.cb = vmi.buf_length;
  assert(!(rc=VioGetPhysBuf(&vpb, 0)));
  result = (rc!=0) ? NULL : MAKEP(vpb.asel[0], 0);
  logEntry(hlLog, TRACE, "GetPhysBuf returning : %p", result);
  return result;
}

void main (void)
{
  PBYTE ScreenBuffer;
  UCHAR pfLock;
  APIRET rc;

  rc = logOpen(&hlLog, TRACE, "LOGFILE", "DEMO");
  assert(!(rc=VioScrLock(LOCKIO_NOWAIT, &pfLock, 0)));
  assert(pfLock==LOCK_SUCCESS);
  ScreenBuffer=GetPhysBuf();
  *ScreenBuffer='A';
  /* call to nonexistant ReleasePhysBuf() */
  assert(!(rc=VioScrUnLock(0)));
  rc = logClose(&hlLog);
}

and here is logfile:

Sun Oct  1 08:45:43 1995 DEMO:P Log file "LOGFILE" opened.
Sun Oct  1 08:45:43 1995 DEMO:P Log level set to trace.
Sun Oct  1 08:45:43 1995 DEMO:T vmi.buf_addr : B8000
Sun Oct  1 08:45:43 1995 DEMO:T vmi.buf_length : 32768
Sun Oct  1 08:45:43 1995 DEMO:T vmi.full_length : 8096
Sun Oct  1 08:45:43 1995 DEMO:T GetPhysBuf returning : 9F0000

--- Maximus/2 3.00