Browse Prior Art Database

Safe and Quick Method of Switching VGA Screen Modes

IP.com Disclosure Number: IPCOM000112740D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Satoh, T: AUTHOR

Abstract

This article describes a method to switch a VGA (SVGA) mode to another one without using the Set Video Mode function (INT 10h, AH=0). Instead of using the function, this method uses the Save/Restore Video State function (INT 10h, AH=1Ch). First, maybe the beginning of a program, it saves the video state (VGA registers and BIOS data). Then the program restores the video state which has been saved at the first step when the program switches the video mode.

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Safe and Quick Method of Switching VGA Screen Modes

      This article describes a method to switch a VGA (SVGA) mode to
another one without using the Set Video Mode function (INT 10h,
AH=0).  Instead of using the function, this method uses the
Save/Restore Video State function (INT 10h, AH=1Ch).  First, maybe
the beginning of a program, it saves the video state (VGA registers
and BIOS data).  Then the program restores the video state which has
been saved at the first step when the program switches the video
mode.

      LIST attached below shows an example of the implementation.  At
the part-1, the program sets the screen to mode 3 (1), blanks the
screen (2), and saves the video state (3).  The part-1 is to be
executed once.  At the part-2, which may be executed several times,
the program restores the video state (4) then enables the VGA screen
(5).

      This method gives a great benefit to programs which may
frequently change the screen mode.  A hot-key operation is an
example.  The application user may often change the screen by
pressing a hot-key.  If the program sets the screen by using the Set
Video Mode function, it takes time to change the screen and/or the
screen may flash for short time when switching the screen mode.  The
method using the Save/Restore function is faster and usually we will
not see the screen flash.  In addition to this, the method sets the
same parameters to the VGA registers as the Set Video Mode function
does.  This me...