New VGA console coming

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

Hi!

   It's been some time since I have posted here with what I'm doing. At
first I was playing with the idea of a universal VC switching function.
This lead to my discovery of how vgacon and screenbuf inter act. TO
discribe what my goals are I have to first describe what I understand of
the console system. If I have a misconcept tell me I'm wrong.

   In the current console system (ruby) each struct vc_data represents
each vitrual console. Only one is active at a time on each VT. Now each 
struct vc_data has a vc_screenbuf which is a shadow buffer where text
values are stored. This allows text to be written to non visible consoles.
Only for the visible VC is the text inside of show buffer is actually
drawn with functions defined in struct consw. 
   This is true for all drivers except vgacon. Why? Because the console
system was originally designed around the VGA text hardware mode. Because
of this the shadow buffer layout matches the VGA text mode layout. Now to
describe this shadow buffer. The shadow buffer is a buffer that is x
columns wide and y rows high. For normal VGA text mode this is usually
80x25.

 80 columns wide

-----------------
|		|
|		|  25 rows. 
|		|  
|		|
-----------------

So the shadow buffer is (80x25 * 2) wide. The reason for the 2 is each
component is 16 bits wide. The high 8 bits represent the text attributes.
These are blinking, underline etc. The low 8 bits represent the text
value, usually a acsii character. For vgacon the shadow buffer of the
visible VC points directly to the VGA text buffer. Now VGA hardware has
built in font images. So a mapping happens from the value in buffer to the
font images in the cards memory.
   
   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?


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