Re: New VGA console coming

[James S. <jsi...@ac...>]

> >    Now for the next step in the evolution of the console system. Well I
> > made a discovery today. Their exist vga cards (JEGA, AX-VGA) that can 
> > display asian characters. I also discovered some old BIOS calls that might
> > lead to figuring out if double byte fonts could be supported. The BIOS
> > call int 10h, ah=18h, al=0,1 which can get/set a font pattern. This leads
> > to me to believe it might be possible for VGA to support double byte
> > fonts. This of course would mean a rethinking of how the shadow buffer
> > should be done. Any ideas anyone?
> 
> Well, it might be possible, though I never have seen a card that would
> be capable of that. Even the version of Ralf Brown's interrupt list
> doesn't say anything about that.

It is there. Int 10/AH=18h. Their is also a AH=19h (Japanese VIDEO -
DOUBLE-BYTE CHARACTER SET SHIFT). Not much info tho :-( As for the 
text modes (mode 52h) that support 16 bit characters appears to be
actually vga 16 color graphics modes. I still like to know where those
extra fonts are stored. Maybe in regular memory. We do have vgafb which
could be made to support 16 bit characters. Since vgafb is supported on 
any platform that vgacon is this expands the range of languages linux can
support. The only problem is ...

> What might be interesting, though, is using the feature that int 10, ah
> 11, al 3 allows. It can be easily set via registers as well.
> 512-character font could be very useful for Unicode mappings.
>
> Another cute feature possible would be to use the font page in the VGA
> card (be it 256 or 512 characters) as a cache of letter images, and only
> use those that are displayed on screen. This would allow using huge
> fonts (> 512 chars), assuming that one never uses all the letters at
> once. Full Unicode support, for example. 

... how to handle so many fonts. I like the idea of a cache of X amount of
characters. Even for fbcon this would be useful. As for the layout of the
shadow buffer. We really need to reconsider its layout. With the idea of
a font cache how about this. 16 bits is used to represent each character. 
The high 8 bits are a index to different font caches. This allows 256
different font caches. The lower 8 bits acts as a index into the font
cache. Now what to do with the attributes? The idea of having 24 bits to
represent a text charachter botehrs me. I prefere if it was 32 bits. We
have to do alot of shifting bits around to get to work otherwise. 

MS: (n) 1. A debilitating and surprisingly widespread affliction that
renders the sufferer barely able to perform the simplest task. 2. A disease.

James Simmons  [jsi...@li...]               ____/| 
fbdev/console/gfx developer                             \ o.O| 
http://www.linux-fbdev.org                               =(_)= 
http://linuxgfx.sourceforge.net                            U
http://linuxconsole.sourceforge.net