SAMPLE: VxD Helps MS-DOS Application Query Screen State

• Microsoft Windows Device Development Kit (SDK) for Windows versions 3.0 and 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 is a file in the Microsoft Software Library that contains a virtual device (VxD) that provides this information and a sample MS-DOS application that uses the VxD services.

MORE INFORMATION

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

• Allocate_Device_CB_Area
• Hook_Device_Service
• Get_Next_VM_Handle
• Test_Cur_VM_Handle

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

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.

Download VWFD.EXE, a self-extracting file, from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download VWFD.EXE (size: 28614 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \softlib\mslfiles directory
        Get VWFD.EXE (size: 28614 bytes)