VWFD: A VxD that Reports a VM's Windowed vs. Full-Screen
State

Revised: February 1993

VWFD is the virtual windowed/full-screen device. When
installed on a system running Microsoft(R) Windows(TM) in
enhanced mode, VWFD allows MS-DOS(R) applications to
determine whether they are running full screen or in a
window. VWFD supplies the following callback to accomplish
this:

     call:  VWFD_API_Callback
     entry:  BX=VMID of the virtual machine (VM) to test
     exit:  AX=0 if VM is full screen

VWFD uses the following virtual machine manager (VMM)
services:

>  Allocate_Device_CB_Area
>  Hook_Device_Service
>  Get_Next_VM_Handle
>  Test_Cur_VM_Handle

TSTWF.ASM is a sample MS-DOS program that uses the VWFD
callback to find out if it is being run in a windowed or
full-screen VM. TSTWF uses the following functions:

>  Interrupt 2Fh, AX=1600h -- Determine if enhanced-mode
Windows is running.
>  Interrupt 2Fh, AX=1684h -- Get VxD function callback
address.


To build VWFD:

You will need Microsoft Macro Assembler version 6.0 or
higher, as well as some special tools and include files;
see the "VxD Tools" and "VxD Include Files" abstracts to
copy these files to your development system. Configure
your development environment as described in the "VxD-Lite
Mini-DDK" technical article on the Microsoft Developer
Network CD.

If you have the Windows version 3.1 Device Driver Kit
(DDK), you can build its version of VWFD using the DDK-
supplied MASM5.EXE (a special version of Macro Assembler
version 5.10). Note that the DDK samples require a
specific structure for the source and include
subdirectories, whereas the corresponding samples in the
"VxD-Lite Mini-DDK" utilize the INCLUDE environment
variable to give you more flexibility in structuring your
development files.


To execute VWFD:

1.  Run VWFD.EXE from the MS-DOS prompt before starting
Windows. When enhanced-mode Windows starts up, the VxD
will load automatically. Thus, you do not need to modify
the SYSTEM.INI file to load this VxD. VWFD will
automatically load each time you start Windows until you
reboot your computer; once rebooted, the stub loader is
cleared from memory and the VxD will not load.

If you prefer to have Windows load the VxD without first
executing it from the MS-DOS prompt, rename VWFD.EXE to
VWFD.386 and move it to the Windows SYSTEM subdirectory.
Add the line DEVICE=VWFD.386 to the [386Enh] section of
the SYSTEM.INI file and restart Windows.

2.  Run Windows in enhanced mode. The code responsible for
self-loading the VxD is in the VXDSTUB.ASM file and is
linked into the final VxD file by the STUB 'VXDSTUB.EXE'
module definition (.DEF) file statement. When executed
from the MS-DOS prompt, the VxDStub hooks Interrupt 2Fh,
terminates, and stays resident. When Microsoft Windows
initializes itself, the TSR responds to the Interrupt 2Fh,
AX=1605h broadcast and returns a structure that causes the
VxD to be loaded. This technique is discussed in the "TSR
Support in Microsoft Windows Version 3.1" technical
article on the Microsoft Developer Network CD.

3.  Run an MS-DOS VM (for example, COMMAND.COM), and run
TSTWF.EXE in it. TSTWF will report whether the VM is
windowed or full-screen.

4.  Press ALT+ENTER to toggle the VM between windowed and
full-screen mode, then run TSTWF.EXE again; it should
report the opposite state.

VWFD was built and tested under Microsoft Windows version
3.1 using Microsoft MASM versions 6.0 and 6.1 and the
tools and include files provided in the "VxD-Lite Mini-
DDK."

KEYWORDS: PR-CD1; CD3 (revised)

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