🚀 go-pugleaf

In article <HENRIK.JOHANSSON.92Sep2140043@ariel.nexus.comm.se>, Henrik.Johansson@nexus.comm.se (Henrik Johansson) writes:
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|> From: Henrik.Johansson@nexus.comm.se (Henrik Johansson)
|> Subject: Changing and restoring Video Mode
|> Message-ID: <HENRIK.JOHANSSON.92Sep2140043@ariel.nexus.comm.se>
|> Sender: news@c3consult.comm.se
|> Organization: Communicator NEXUS AB, Uppsala, Sweden
|> Distribution: comp
|> Date: Wed, 2 Sep 92 09:00:43 GMT+5:00
|> Lines: 18
|> 
|> 
|> How do I save _all_ relevant information about current video mode so
|> that I can restore it afterwards exactly as it was?
|> 
|> This problem comes from a Device Driver that is triggered and needs
|> some input from the user.  Therefore the screen gets blanked, user
|> input requested, some action taken, and afterwards the driver must
|> return to wherever the pc was running with the video mode completely
|> intact.
|> 
|> Anyone?
|> 
|> /hj
|> --
|> Real life:   Henrik Johansson            Email:  Henrik.Johansson@Nexus.Comm.SE
|> Snailmail:   Communicator Nexus          Phone:  +46 18 171811
|>              Box 857                     Fax:    +46 18 696516
|>              S - 751 08 Uppsala, Sweden
|> 

Hi.  You need to save the video-relevant variables in the ROM-BIOS data area
(at segment 40h), all the VGA registers (you can't do this on an EGA since
most of them are write-only), and the entire video buffer (which can be
anything between 256K to 4 megabytes depending on the adapter).

Then set the mode you want and do anything you like.

Then use the ROM-BIOS to put the mode back to what it was before (which is one
of the variables in the saved copy of the ROM-BIOS data area but you could have
also just gotten it with INT 10h function 0Fh), copy the ROM-BIOS data back,
copy the registers back, and copy the video buffer back (and be sure to restore
the registers you used to traverse the video buffer).

I know it's complicated (and possibly memory-comsuming) to be able to swap
over any text or graphics mode on any adapter, but you would need to code your
(interrupt?) handler to refuse to swap over any mode you don't recognize.  And
you could make it a whole lot simpler just by refusing to swap over any graphics
mode (i.e. you'd only have to swap 80x25x2 bytes rather than 256K or more).

Tschuess,
David Paschal