EAX = VDD_DRIVER_REGISTER equate (80H)
EBX = Magic Number
ECX = Total bytes used by the visible Windows screen
EDX = 0 if the mini-VDD supports VGA 4 plane virtualization in a window or -1 if the display requires that VGA 4 plane graphics programs run full-screen and can not be windowed.
ES:DI Pointer to ResetHiResMode which is a required Display driver function which will be called by the VDD in order to reenable the display hardware for Windows high resolution mode after returning from a full-screen MS-DOS virtual machine.
EAX = Total bytes of memory used by the screen (as passed in ECX to the function) plus the number of bytes used by the VDD for virtualizing VGA 4 plane graphics in a window.
EAX = VDD_DRIVER_REGISTER if you are running with a Windows 3.1 VDD and not the Windows 95 VDD. This means that the user somehow has installed the wrong VDD.
This routine should be called immediately after the Windows high resolution (hi-res) mode has been set by the display driver. The mini-VDD's function GET_VDD_BANK is called by this routine.
ResetHiResMode is a required display driver entry point which must be placed in a FIXED code segment in the display driver. It is called by the Windows 95 VDD in order to place the screen back into Windows hi-res mode after a user presses ALT-TAB or ALT-ENTER to switch away from a full screen MS-DOS session. ResetHiResMode typically is a simplified Enable call which reinitializes the hardware including the palette DAC and hardware cursor so that Windows will run again.
To support Far East DBCS, the display hardware and mini-VDD should be able to support VGA graphics in a window. The VDD supports VGA graphics in a window by allocating a 32K or 64K block of video memory right below the visible Windows screen. The mini-VDD then sets access to this memory (usually by banking it into physical address A000h) and allows planar access to this memory while maintaining the packed pixel Windows screen visibly. However, some hardware cannot simultaneously have the VGA data pathway and the packed-pixel hi-res pathway running. If your hardware cannot, set EDX to -1 and the VDD will not attempt VGA virtualization in a window.
This function calls the mini-VDD function GET_VDD_BANK.
GET_VDD_BANK