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From: eyal AT ise DOT canberra DOT edu DOT au (Eyal Lebedinsky)
Newsgroups: comp.os.msdos.djgpp
Subject: graphics in v2: some answers
Date: 29 Dec 1995 12:19:25 GMT
Organization: Eyal at home
Lines: 46
Sender: eyal AT e5 DOT pcug DOT org DOT au (Eyal Lebedinsky)
Message-ID: <4c0mcd$dev@supreme.pcug.org.au>
NNTP-Posting-Host: ts109.pcug.org.au
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

I was asking a few questions while I worked my way through the maze.
I now got my program working rather well.

I learnt a few things on the way, and I will post a demo program
extracted from my code to demonstrate it.

v2 does not support banked video memory automatically, but I already
had the program take care of that. Now I needed to get fast access
to the video bank memory (normally at real address 0xa0000). I decided
to map it the near data so that I can access like normal memory without
the special far memory macros. This worked very well.

I then grabbed the VBE 2.0 spec and had a quick read (this spec is
not that hard to read). I then proceeded to verify what it says - I
used univbe 51a (I think a beta release?) and found that it did not
follow some of the rules. So one must be careful not to trust what
the doco says at every step. Check the situation each time.

I calles VBE function 0x4f0a (get protected mode table) which gave me
the address of a table and it's size. I then grabbed it into my
nead memory (this time copied with dosmemget()) and inside there
are found the magical routines to do banks switching, page flipping
(set screen start) and more. I then wrote a tiny asm stub to handle
the call (they are not C callable) and presto, it worked (well, after
many frustrating, hair tairing faults and what not, but who remembers?).

I now managed to do bank swapping in three ways:

1) in10 function 0x4f05 (VBE standard). This is time consuming due to the
   need to  real/prot switching.

2) call the VBE1.2 realMode function. This is only marginally faster
   that using the interrupt.

3) call the VBE 2.0 prot mode function. This is blazingly fast.

So far, the set-screed-start prot mode function does not seem to
function as documented (either I call it wrongly or it does not
work for my card with this version of univbe).

The above stuff will be soon in the beta Fly8 relaese on:
	csc.canberra.edu/pub/ise/eyal/fly8/beta
in the sources archive, under fly8/djgpp/grvbe.c

--
Eyal Lebedinsky		(eyal AT ise DOT canberra DOT edu DOT au, eyal AT pcug DOT org DOT au)