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Microsoft KB Archive/139292

From BetaArchive Wiki

BUG: VMD_Post_Absolute_Pointer_Message Bug in VMOUSE


The information in this article applies to:

  • Microsoft Win32 Device Driver Kit (DDK) Windows 95


The VMOUSE VxDCall VMD_Post_absolute_Pointer_Message does not correctly call the USER API Mouse_Event as documented in the MSDN Library compact disc and elsewhere. The other VxD calls to VMOUSE are not affected by this problem. Programmers using the Mouse_Event call to the USER API directly as from a DLL are not affected by this problem.


The developers generated the following workaround sample code. In general, it ends up calling the Mouse_Event API. A number of customers have used this sample to guide them and have met with success. There are, however, two important caveats:

  • The value in VMOUSE_FOCUS_VM is never initialized. In your initialization code, you should default it to the current VM by using something like this:

       VMMcall Get_SYS_VM_Handle
       mov [VMOUSE_FOCUS_VM],ebx 
  • The hook call VMMCall Hook_Device_PM_API does not currently have a corresponding unhook call. Therefore your VxD will need to be static.

Sample Code

; Microsoft Corp. (C) 1991-1996
; Your driver may already have the following code to track MOUSE
; Ownership. This code needs to be there because even as advertized, VMD_
; Post_Absolute_Message won't handle MS-DOS VMs. So your VxD needs to track
; mouse ownership and selectively call VMD_Post_Absolute_Pointer_Message
lpfnPreviousVMOUSEPMAPI   dd   0   ; VMOUSE's PM_API_Proc
               ; will be non-zero if you hook vmouse.

UserEventHandle   dd   0
User_Mouse_Event_Segment   dd   0
User_Mouse_Event_Offset      dd   0
;In the Device_Init (or sys_dynamic_Device_init, if it
;is a dyna-loaded VxD (loaded by vmouse)) proc of your VxD,
   VxDCall   VMD_Get_Version      ; get version of
   cmp   eax, 400h      ; Q: correct support ABS coords?
   jne   done         ;   Y: Get out
   mov   eax, VMD_Device_ID      ; N: hook vmouse's service.
   mov   esi, OFFSET32 FTG_PM_API
   VMMCall   Hook_Device_PM_API      ; Hook VMOUSE's PM
   mov   [lpfnPreviousVMOUSEPMAPI], esi   ; Save old address
; Now on to FTG_PM_API. This will watch for Mouse.drv telling VMOUSE
; about User.exe's entry point. This entry point used to be called
; by your Mouse.drv in Windows 3.1.
BeginProc FTG_PM_API
   movzx   eax, [ebp.Client_AX]
   jne   @F
   movzx   eax, [ebp.Client_DX]
   mov   [USER_Mouse_Event_Offset], eax
   mov   eax, [ebp.Client_ECX]
   mov   [USER_Mouse_Event_Segment], ax
   jmp   goto_previous
   jne   goto_previous
   mov   eax, [ebp.Client_EBX]      ; contains the VM handle
   mov   [VMOUSE_FOCUS_VM], eax
   jmp   [lpfnPreviousVMOUSEPMAPI]
; Now on to mouse focus tracking. FTG needs to track mouse
; focus, because if the mouse focus is on SYS_VM, then it
; wants to handle the absolute device in one way, otherwise
; in a different way.
; Add to your CONTROL_PROC, the following line:
   Control_Dispatch Set_Device_Focus, FTG_Set_Device_Focus
; On to FTG_Set_Device_Focus
BeginProc FTG_Set_Device_Focus
   or   edx, edx      ; Q: Critical set focus ?
   jz   fsdf_set      ;    Y: set it
   cmp   edx, VMD_Device_ID   ;    N: Q: Is it for VMD ?
   jne   fsdf_exit
   mov   [VMOUSE_FOCUS_VM], ebx
EndProc FTG_Set_Device_Focus
; All the previous code needed to be there in your VxD anyway because,
; even as advertized, VMD_Post_Absolute_Pointer_Message, didn't work for
; MS-DOS VMs. The following code will circumvent VMD_Post_Abso...
; Say that you are at this decision point
; Q: Should I call VMOUSE or should I do the relative motion stuff
;    or whatever for the MS-DOS VMs ?
   mov   ebx, [VMOUSE_FOCUS_VM]
   VMMCall   Test_Sys_VM_Handle   ; Q: Is this System VM ?
   jnz   Handle_DOS_VMs      ;    N: do what you would have done.
; Handle Windows VM absolute motion here.
; Assumption: You are at interrupt time. AND
; Buttons = button state (button state as desired by User.exe's
;          mouse_event procedure.)
;       (without the absolute bit set).
; XPos = X position
; YPos = Y position
   xor   eax, eax
   cmp   [lpfnpreviousVMOUSEPMAPI], eax   ; Q: good vmouse ?
   je   call_it
   cmp   [UserEventHandle], eax      ; Q: Event scheduled already?
   jne   handled_it
   mov   esi, OFFSET32 CallUserProc
   mov   ecx, PEF_Wait_For_STI OR PEF_Always_Sched
   VMMCall   Call_Priority_VM_Event
   mov   [UserEventHandle], esi
   jmp   handled_it
   mov   al, [Buttons]
   mov   esi, [XPos]
   mov   edi, [YPos]
   VxDCall   VMD_Post_Absolute_Pointer_Message

handled_it:               ; handled hardware int.


; Now on to the final part. Call User.exe's mouse_event proc
BeginProc CallUserProc
   movzx   ecx, [USER_Mouse_Event_Segment]
   jecxz   cup_done
   VMMCall   Begin_Nest_Exec
   movzx   eax, [Buttons]      ; buttons
   or   ax, 8000h      ; set absolute bit
   mov   [ebp.Client_EAX], eax
   mov   eax, [XPos]      ; send X position
   mov   [ebp.Client_EBX], eax
   mov   eax, [YPos]      ; send Y position
   mov   [ebp.Client_ECX], eax

   movzx   eax, [ButtonCount]   ; How many buttons ?
   mov   [ebp.Client_EDX], eax   ; send # buttons
   xor   eax, eax
   mov   [ebp.Client_EDI], eax   ; These need to be 0
   mov   [ebp.Client_ESI], eax

   mov   edx, [USER_Mouse_Event_Offset]   ; ECX Still contains SEGMENT

   VMMCall   Simulate_Far_Call
   VMMCall   Resume_Exec

   VMMCall   End_Nest_Exec

   mov   [UserEventHandle], 0      ; Reset flag so new messages
                                   ; can go in

EndProc CallUserProc 


Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.


MSDN Library Compact Disc October 1995

Additional query words: 4.00 absolute VxD win95

Keywords :
Issue type :
Technology : kbAudDeveloper kbWin95search kbWinDDKSearch kbWin32sSearch kbWin32DDK95 kbWin32DDKSearch

Last Reviewed: March 4, 1999
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