VioRegister

This call registers an alternate video subsystem within a session.

VioRegister (ModuleName, EntryPoint, FunctionMask1, FunctionMask2)

• ModuleName (PSZ) - input: Address of the ASCIIZ string containing the 1-8 character file name of the subsystem. The maximum length of the ASCIIZ string is 9 bytes including the terminating byte of zero. The module must be a dynamic link library but the name supplied must not include the .DLL extension.
• EntryPoint (PSZ) - input: Address of the ASCIIZ name string containing the dynamic link entry point name of the routine in the subsystem to receive control when any of the registered functions is called. The maximum length of the ASCIIZ string is 33 bytes including the terminating byte of zero.
• FunctionMask1 (ULONG) - input: A bit mask where each bit identifies a video function being registered. The bit definitions are shown below. The first word pushed onto the stack contains the high-order 16 bits of the function mask, and the second word contains the low-order 16 bits.

• FunctionMask2 (ULONG) - input : A bit mask where each bit identifies a video function being registered. The bit mask has the format shown below. The first word pushed onto the stack contains the high order 16 bits of the function mask, and the second word contains the low order 16 bits. Unused bits are reserved and must be set to zero.

rc (USHORT) - return:Return code descriptions are:

• 0 NO_ERROR
• 349 ERROR_VIO_INVALID_MASK
• 403 ERROR_VIO_INVALID_ASCIIZ
• 426 ERROR_VIO_REGISTER
• 430 ERROR_VIO_ILLEGAL_DURING_POPUP
• 465 ERROR_VIO_DETACHED
• 494 ERROR_VIO_EXTENDED_SG

An alternate video subsystem must register which video calls it handles. The default OS/2 video subsystem is the Base Video Subsystem.

When any of the registered functions are called, control is routed to EntryPoint. When this routine is entered, four additional values (5 words) are pushed onto the stack.

The first value is the index number (Word) of the routine being called. The second value is a near pointer (Word). The third value is the caller's DS register(Word). The fourth value is the return address(DWord) to the VIO router.

For example, if VioSetCurPos were a registered function, the stack would appear as if the following instruction sequence were executed if VioSetCurPos were called and control routed to EntryPoint:

 PUSH     WORD     Row
 PUSH     WORD     Column
 PUSH     WORD     VioHandle
 CALL     FAR      VioSetCurPos
 PUSH     WORD     Index
 CALL     NEAR     Entry point in Vio router
 PUSH     WORD     Caller's DS
 CALL     FAR      Dynamic link entry point

The index numbers that correspond to the registered functions are listed below:

When a registered function returns to the video router, the return code is interpreted as follows:

• Return code = 0 : No error. Do not invoke the corresponding Base Video Subsystem routine. Return to caller with Return code = 0.
• Return code = -1 : No error. Invoke the corresponding Base Video Subsystem routine. Return to caller with Return code = return code from Base Video Subsystem.
• Return code = error (not 0 or -1) : Do not invoke the corresponding Base Video Subsystem routine. Return to caller with Return code = error.

When an application registers a replacement for VioPopUp within a session, the registered routine is only invoked when that session is in the foreground. If VioPopUp is issued when that session is in the background, the OS/2 default routine is invoked.

An alternate video subsystem should be designed so the routines registered do not cause any hard errors when they are invoked. Otherwise, a system lockout occurs. Code and data segments of registered routines, that might be loaded from diskette, must be preloaded.

All VIO functions within a session are serialized on a thread basis. That is, when an alternate video subsystem receives control, it can safely assume that it is not called again from the same session until the current call has completed.

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