VWFD.exe VxD Helps MS-DOS Application Query Screen State
ID: Q67590
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The information in this article applies to:
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Microsoft Windows Device Development Kit (DDK) for Windows, versions 3.0, 3.1
SUMMARY
The enhanced mode Microsoft Windows environment does not provide any
facility through which an MS-DOS (non-Windows) application can determine
whether it is running in a window or full screen. VWFD.exe is a file that
contains a virtual device (VxD) that provides this information and a sample
MS-DOS application that uses the VxD services.
MORE INFORMATIONThe following files are available for download from the Microsoft
Download Center. Click the file names below to download the files:
Vwfd.exe For more information about how to download files from the Microsoft
Download Center, please visit the Download Center at the following Web
address
http://www.microsoft.com/downloads/search.asp
and then click How to use the Microsoft Download Center.
VWFD is the virtual windowed/full-screen device. When installed on a system
running Microsoft Windows in enhanced mode, VWFD allows MS-DOS 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:
- 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.
- 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.
- 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.
- 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."
Additional query words:
Keywords : kbfile kbsample kb16bitonly kbDDK kbWinOS3
Version : :3.0,3.1
Platform :
Issue type : kbinfo
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