Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

                                                     ◄Up► ◄Next► ◄Previous►
────────────────────────────────────────────────────────────────────────────
 
The grabber calls several virtual-display device functions to carry out
requests to update, paint, or grab the screen. To call a virtual-display
device function, the grabber first retrieves the virtual-display device
entry point address using Get Device Entry Point Address (Interrupt 2Fh
Function 1684h). The grabber then can set registers and call the address to
carry out a function.
 
The grabber calls the Get_Version function to verify that it is matched with
the correct virtual-display device. Whenever the grabber needs access to the
video memory or the video controller context, it queries the virtual display
device. The virtual-display device returns a structure describing the
requested memory or controller context.
 
The grabber calls the Get_Mem function to get the current contents of the
video memory while updating the windowed display. The grabber calls the
Get_GrbMem function to get a snapshot of the entire screen in response to
the user pressing the ALT+PRNTSCRN key combination in a full-screen VM. The
grabber calls the Free_Mem and Free_Grab functions to tell the
virtual-display device that the grabber is no longer using this memory.
Get_State and Get_GrbState return the current and grabbed controller
context, respectively.
 
The grabber calls the Get_Mod function to update the windowed display
incrementally. Get_Mod returns a structure that indicates modifications to
the current display. The grabber modifies only those parts of the window
that have changed, and then calls the Clear_Mod function to inform the
virtual-display device that the modifications have been carried out.
 
To make sure that the video memory or context will not change when the
grabber is accessing the memory, the VM should suspend operations
immediately after a call to the Get_Mem or Get_Mod function. The VM can
continue operations only after a call to the Free_Mem function or an
explicit call to the Unlock_App function from the grabber.
 
 
                                      ♦