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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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