with DOS/4GW? - Open Watcom

DOS Programming Guide
ftp://ftp.intel.com/pub/IAL/software specs/dpmiv1.zip
This ZIP file contains a Postscript version of the DPMI 1.0 specification.
5.2 How can I write directly to video memory using a
DOS extender?
Many programmers require access to video RAM in order to directly manipulate data on the
screen. Under DOS, it was standard practice to use a far pointer, with the segment part of the
far pointer set to the screen segment. Under DOS extenders, this practice is not so standard.
Each DOS extender provides its own method for accessing video memory.
5.2.1 Writing to Video Memory under Tenberry Software DOS/4GW
Under DOS/4GW, the first megabyte of physical memory is mapped as a shared linear
address space. This allows your application to access video RAM using a near pointer set to
the screen’s linear address. The following program demonstrates this method.
/*
SCREEN.C - This example shows how to write directly
to screen memory under the DOS/4GW dos-extender.
Compile & Link: wcl386 /l=dos4g SCREEN
*/
#include
#include
/*
Under DOS/4GW, the first megabyte of physical memory
(real-mode memory) is mapped as a shared linear address
space. This allows your application to access video RAM
using its linear address. The DOS segment:offset of
B800:0000 corresponds to a linear address of B8000.
*/
#define SCREEN AREA 0xb800
#define SCREEN LIN ADDR ((SCREEN AREA)