Call With
EAX = VDD_REGISTER_SSB_FLAGS equate (84H)
EBX = Magic Number
DS:SI = Pointer to SaveScreenBitmap flag byte (see below).
Return Values
Nothing destroyed.
Remarks
Because many display drivers implement the SaveScreenBitmap function and because they want to maximize the amount of off-screen memory available for SaveScreenBitmap, the Main VDD allows the display driver to register the address of a byte flag in the display driver's fixed data segment which controls the operation of SaveScreenBitmap.
This flag has three bits that the VDD and/or SaveScreenBitmap interact with:
Bit 0 | (called SHADOW_EXISTS in VGA.DRV) flags that the display driver could potentially use off-screen memory for SaveScreenBitmap use. This flag is ignored by the VDD at this time. |
Bit 1 | (called SHADOW_IN_USE in VGA.DRV) flags that SaveScreenBitmap has something saved in the off-screen memory area. The VDD checks this flag before setting the SHADOW_TRASHED flag to see if SaveScreenBitmap is using that area. |
Bit 2 | (called SHADOW_TRASHED in VGA.DRV) flags that someone other than SaveScreenBitmap (in our case the VDD's VGA virtualization routines) has destroyed a bitmap which SaveScreenBitmap has saved in the off-screen area. The VDD sets this bit when it uses the off-screen memory for VGA virtualization. |
No mini-VDD functions are called during this function.