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    {
    From: myles@giaec.cc.monash.edu.au (Myles Strous)

             DOS Super VGA / VESA programming notes - by Myles.
             --------------------------------------------------

             Send updates and errors to myles@giaec.cc.monash.edu.au
             Comments on my grammar and style are not welcome. 8-)

             These notes currently only cover the high-resolution
             256-colour modes.  I may extend that to HiColor and TrueColor
             modes if and when I get the time.  (If anyone else wants to
             do that bit, feel welcome !)

             This document is meant to be a pointer, not a comprehensive
             treatise.

             My information base is biased by my Turbo Pascal hobbyist's
             background. Please feel free to send me corrections or
             updates.

             Introduction:
             -------------

             SuperVGA programming uses screen data that can easily exceed
             1 MB in size. However, the normal VGA card only offers a 64k
             memory access at A000h (some cards provide 128k).

             How do you get to all that video memory ?
             You know it's there - after all, your card documentation states
             that you have e.g. 512k of memory on your video card, enough to
             handle e.g. 800 x 600 x 256.

             You may even have experimented and found that you can change to
             this mode, but can only write pixels to a narrow band at the
             top of the screen.(Surprise! That narrow band is 64k in size.)
             (Except, of course, if it 128k - read on.)

             The answer is in a technique called bank switching, where you
             use the 64k at A000h as a window onto your video card's memory.

             The techniques and functions to do this vary from card to
             card, because of historical reasons. Read on.

             History:
             --------

             IBM defined MDA (monochrome), CGA, EGA, the MCGA (found  in
             some early  PS/2  models,  it  never  became  a  wide-spread
             standard), and in 1987, the VGA (and the 8514/A).

             VGA was backwards compatible with all the previous standards,
             including the   320x200,256-colour   MCGA   mode.  It  also
             introduced a new mode, 640x480 with 16 colours,  which  was
             basically an extension of EGA's 640x350,16-colour mode, with
             one major advantage - square pixels (so that if you plotted
             the points  for  a  circle,  it looked like a circle, not an
             ellipse). There was also a 640*480 2-colour mode on the MCGA.

             If you wanted higher resolutions you had to pay quite a bit
             for IBM's   professional   level   card,   the   8514/A,  a
             high-resolution card capable  of  256-colour  modes  up  to
             1024x768 (interlaced).
             However, this card was proprietary - IBM didn't
             release the register-level details.

             Each of the other video card manufacturers then came up with
             their own  high  resolution  cards.  However,  they were all
             implemented differently.   640x480  in  256  colours,  for
             example, may  have been mode 34h on one manufacturer's card,
             mode 56h on another's, and mode 62h on yet another.   (N.B.
             These are just false numbers to give you the idea.) Similarly
             for 800x600, 1024x768, and other modes.

             Also, some manufacturers implemented 128k banks. Manufacturers
             also differed on whether banks (as a subsection of the video
             card's memory) could start only 64k apart, or 4k apart (i.e.
             possibly overlapping), or ....
             You get the picture. Non-standard.

             That 64k of memory:
             -------------------

             For 256-colour modes, each byte in  the  64k  is  simply  a
             palette value,  or  the  colour  number  of  a  pixel  (Yes,
             256-colour graphics is just pixel painting by the numbers).
             This means  the  number  is  just  an array index into a 256
             member array of 6-bit red, green and blue values, giving you
             256 colours out of 256k (2^18) possible values.

             -------------------------------------------------------------
             HiColor and  TrueColor  cards use a different RAMDAC chip (a
             digital to analogue chip converting the digital  values  in
             video memory to analogue output for the monitor).

             HiColor and TrueColor modes represent their colours directly
             - you  specify  the  red-green-blue  values  for each pixel,
             rather than choosing from a limited array of colours.

             15-bit modes provide 32k colours - each colour is represented
             as a  two-byte  value  xrrrrrgggggbbbbb,  where the x bit is
             unused.  16-bit modes provide 64k colours, and  provide  an
             extra bit  for  green  (I think) - rrrrrggggggbbbbb.  24-bit
             modes use three-byte values, one byte (8-bits) each for red,
             green, and blue.

             SuperVGA does not support the 32-bit and 64-bit modes found
             on some specialist hardware, although you may sometimes find
             32-bit (and maybe even 64-bit ?) files.
             Some SuperVGA cards e.g. the S3-864, have pseudo-32-bit
             modes. (Further information, anyone ?)

             32-bits provides another byte for an alpha value - which is a
             transparency value used for overlaying one image on another -
             also good for such things as  anti-aliasing  edges.  64-bit
             values are  like  32-bit,  but provide 2 bytes each for red,
             green, blue, and alpha.
             --------------------------------------------------------------

             Programmers have to write routines to detect  (or  ask  the
             user:-p) which card is present, and then write card-specific
             routines to handle the graphics routines for that card. If a
             new card  comes out, from a different manufacturer or even a
             different model  of  card  from  the  same   manufacturer,
             programmers have to write new routines to support that card,
             which means that first they have to get  details  from  the
             manufaturer, and if they do it properly, they needed to find
             a card to test their routines, (or a beta tester to do it for
             them).  You  could provide these routines either in the body
             of your code, or write external  drivers  or  configuration
             files.  It is possible to write moderately generic code that
             loads the specific details from an external file.

             The manufacturers usually provide drivers for a few programs
             (Autocad, Windows, etc.). Also, the information supplied
             in the user manual that comes with the card is usually only the
             mode numbers for that card, not the bank-switching code. Sigh.

             Not surprisingly, most programs don't support ALL the cards
             available, and  many  programmers  choose not to support any
             SuperVGA cards.   It  isn't  worth  the  effort,  and  your
             customers always  ask  when  you  are going to support THEIR
             particular card.

             The manufacturers were miffed  enough  by  this  that  they
             actually got  together  and  formed  the  Video  Electronics
             Standards Association (VESA).  They defined a new  standard
             programmer's interface so that programmers would only have to
             write one set of graphics routines for SuperVGA.  This  was
             the VESA  standard. It has nothing to do with VESA Local Bus
             (VLB), which is another standard from the same group about a
             completely different  hardware  problem.   (You think that's
             confusing - VESA are coming/have come out with another VESA
             standard for sound device interfacing.) This standard is also
             known as the VESA VBE standard (Video BIOS Extensions).

             The VESA VBE standard implements video card routines through
             an  extension of  the  Interrupt  10h BIOS routines
             (subfunction 4Fh).

             Most video cards in existence implement VESA through the use
             of a  VESA VBE TSR  (TSR = Terminate and Stay Resident
             program, also known as a memory-resident program.), often
             known as a  VESA driver  (not  entirely  accurate), although
             newer video cards may implement the VESA VBE standard in
             hardware.  Let  me  re-iterate that  this  is  an entirely
             different matter from whether they are a VESA Local Bus (VLB)
             card.

             A VESA VBE driver should have been  included  on  the  disk
             of  drivers and utilities you got with your video card.
             However, this, along with a number  of  VESA  VBE drivers
             available  on  Internet, may be out of date.  Most VESA TSRs
             are specific to a particular card.

             If you don't have a VESA VBE driver that provides  support
             for  version 1.2  of the VESA VBE standard, look for a
             shareware VESA utility, last seen as UNIVBE50.ZIP, by Kendall
             Bennett  of  SciTech Software. This is a shareware TSR that
             provides VESA extensions for practically every SuperVGA card
             in existence. Inexpensive personal  registration.  Licences
             available for including it with your own programs.

             The current version of the VESA VBE standard is 1.2 - you
             should really try  and  get a driver which supports version
             1.2, as there are a number of useful extra extensions on
             earlier versions (such as 32k/64k/16.7M colour modes)

             VESA subfunctions (as of VESA standard version 1.2) are:

      subfunction 00 - get SuperVGA information
      subfunction 01 - get SVGA mode information
      subfunction 02 - set SuperVGA video mode
      subfunction 03 - get current video mode
      subfunction 04 - save/restore SuperVGA video state
      subfunction 05 - bank switch
      subfunction 06 - get/set logical scan line length
      subfunction 07 - get/set display start
      subfunction 08 - get/set DAC palette control

             There is supposedly a version 2.0 of the VESA video standard
             coming out, with BitBlt, fillBox, drawLine, etc.

             -----------------------------------------------------------
             A note on VESA and speed :

             Some people who should know better, if they'd bothered to
             stop and think about things, and investigate VESA, have
             stated that programming using the VESA VBE is s-l-o-w,
             apparently because they hear the word "BIOS" and tune out,
             because in the past it has been emphasised that using the
             BIOS to e.g. draw a pixel, is incredibly slow, compared to
             writing your own routines to just move graphics data into
             video memory.

             However, apart from setting values and graphics mode, usually
             at the beginning of your program, and getting information
             pertaining to the mode you are using (a few BIOS calls at
             most, done once only), you don't have to use the BIOS much at
             all. Once you've set a bank, the VESA standard allows you to
             write directly to video memory (well, a 64k subset of it),
             indeed almost encourages it. True, you can use function 05 to
             change banks, but you'll find that the time spent changing
             banks is minimal compared to other aspects of your program,
             e.g. the time spent on floodfills and line drawing, etc.
             However, if you begrudge even the time spent changing banks,
             the VESA VBE standard also includes a function returning the
             direct address of the video card's bank changing routine, so
             you can use it directly in a far call.

             In other words, using the VESA VBE will not slow down your
             program, and will allow it to work on most video cards in
             SuperVGA modes without much extra work from you the
             programmer.

             -----------------------------------------------------------

             Warning: VESA is not a completely simple solution. You have
             to find  out  whether  the  card  it  is being used on has 2
             "windows", whether one or both windows are readable  and/or
             writeable, how  big are the jumps by which you can move the
             window around (granularity), how big the windows are,  etc.
             While these routines will only have to be written once, there
             is a bit of work to be done at the start to make your  VESA
             routines generic to all VESA cards.

             -----------------------------------------------------------

             Information and code.
             ---------------------

      ******  N.B. I am not willing to
      supply FTP sites for these files -
      I suggest you either use ARCHIE, or find out HOW
      to use archie - news.answers and comp.answers may
      be good places to start.
      Requests for FTP sites will be deleted from my mail
      without consideration.

             SVGABG55.ZIP - Jordan Hargrave's set of Super VGA BGI  drivers.
             If your card is not one of those catered for, it will also use
             a VESA driver. Shareware, register for source.  Uses the Graph
             unit.  This is just like using the Borland BGI.

             VESATP11.ZIP - shareware (nagware) TPU , register for source.
             On initialising  a  Super  VGA  mode,  you  get  an SuperVGA
             advertisement for registration.  Otherwise much like the BGI
             interface, except you don't use the Graph unit.

             EGOF11-6.ZIP
             EGOF11-7.ZIP - shareware, Turbo Pascal units. Mode X and VESA.

             VGADOC3.ZIP - includes card-specific information  and  code
             (Turbo Pascal), also includes VESA information and code. Will
             identify your card (including the DAC  -  256  colour,  32k
             colour, 16.7M  colour),  and  let you do a quick demo in all
             available modes. Very extensive, freeware. Top quality.
             Compiler/author, Finn Thoegersen.

             VESASP12.ZIP - an unofficial version of the  official  VESA
             standard, typed  in by a friendly demo coder going under the
             pseudonym of  Patch.   Includes  ASM  information  on  VESA
             routines.

             VESADRV2.ZIP - a collection of VESA drivers, not necessarily
             implementing version  1.2  of  the  VESA  standard. Some, at
             least, are earlier.

             VDRIV.ZIP - an even older collection of VESA drivers.

             VESA24_2.ZIP - C/ASM source for  VESA  usage.
             Originally by Randy Buckland, with modifications by Don
             Lewis.

             VGAKIT52.ZIP - C ?

             SWAG9402.ZIP
             SWAG9405.ZIP - one or both of these collections
             of Turbo Pascal code collections have VESA routines included.

             UNIVBE50.ZIP -  the  universal  VESA   driver.   Shareware
             (advertisement as  TSR  is  loaded).  Regularly  updated and
             improved.  By Kendall Bennett, from SciTech Software.

             MGL - MegaGraphics Library - for C/C++, also  from  SciTech
             Software.

             SVGAKT50 - for C/C++, also from SciTech Software.

             RBNG42 - Ralf Brown's extensive interrupt list in electronic
             form, includes VESA int 10h extensions.

             More details on these and others as and when I have the time.

             -------------------------------------------------------------

             Other sources I have seen/used:
             ------------------------------

             N.B. Only the most recent of these cover up to version 1.2 of
             the standard.

             "PC Interrupts", 2nd ed. by Ralf Brown and Jim Kyle.
             Addison-Wesley, 1994. ISBN 0201624850

             "Super VGA graphics programming secrets" by  Steve  Rimmer.
             Windcrest/McGraw-Hill, 1993. ISBN 0-8306-4427-X (hbk) (C/ASM)
             ISBN 0-8306-4428-8 (pbk)

             "PC INTERN System Programming :  the  encyclopedia  of  DOS
             programming know how" by Michael Tischer. Abacus, 1992. ISBN
             1-55755-145-6 (C/TP/ASM)

            "PC Magazine Turbo Pascal 6.0 : techniques and utilities", by
             Neil J. Rubenking. Ziff-Davis Press, 1991. ISBN 1-56276-010-6

             "Programmer's guide to the EGA and VGA cards", 2nd  ed.  by
             Richard F.  Ferraro. Addison-Wesley, 1990. ISBN

             Program Now (UK  programmer's  magazine),  September  1993,
             p.60-64, Dave  Bolton's  Turbo  Pascal  programming  column,
             "Raising the VESA standard."

             Dr Dobbs Journal, April 1990, p.  65H-70.  "VESA  VGA  BIOS
             extensions :  a  software  standard  for  Super  VGA"  by Bo
             Ericsson.

             This one doesn't have VESA, but it's goes  into  plenty  of
             detail, with  lots  of  code, on programming VGA and earlier
             (ASM/C): "Programmer's  guide  to  the  PC  &  PS/2  video
             subsytems" by  Richard  Wilton.  Microsoft Press, 1987. ISBN
             1-55615-103-9

             ------------------------------------------------------

             The VESA standard itself is available from:

             Video Electronics Standards Association
             2150 North First Street, Suite 440
             San Jose, California. 95131-2029

             Phone (408) 435-0333
             FAX   (408) 435-8225

             You may see an address of South Bascombe Avenue or some such
             quoted in  some sources. This is an old address, and mail is
             no longer forwarded from this address, so don't use it.

             Cost: $20 to non-members, for VBE 1.2

             $50 for the complete VESA Programmers Toolkit, which includes
             VBE 1.2, programmers guidelines for direct color modes, SVPMI
             1.0 SuperVGA protected mode interface, the VESA XGA extensions
             standard, the standard for 800x600 mode (an older one ?), video
             cursor interface and the VGA pass-through connector standard.

             If you are not  USA, add $20 international shipping charge.

             Make sure you  specify  the  VESA  VBE 1.2 standard
             (for VGA BIOS extensions), or the VESA Programmers Toolkit, as
             VESA also has standards for the VESA Local  Bus,  an  audio
             interface, power  management  signalling, and others, all of
             which are "VESA standards". They will FAX you an order form if
             you give them your FAX number.

             ----------------------------------------------------

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