[GEM Development] FreeGEM drivers updated

[Thomas Clayton]

Ahh. _Very_interesting_ (as in "informative"). :-)


I look forward to when I can dig my old "stuff" out of storage and try running some of these. (directly on DOS).

Tom Clayton

BTW: "WOW!", for that 'find' thru Google, too.


--- On Mon, 3/4/13, John Elliott <jce at seasip.demon.co.uk> wrote:

> From: John Elliott <jce at seasip.demon.co.uk>
> Subject: Re: [GEM Development] FreeGEM drivers updated
> To: gem-dev at simpits.org
> Date: Monday, March 4, 2013, 2:24 PM
> 
>   There are a number of reasons why GEM in 256 colours
> may not be optimal. 
> Firstly, it tends to put pressure on memory for things like
> offscreen 
> bitmaps. Secondly, a lot of applications flatly refuse to
> believe in there
> being more than 16 colours / 4 planes. And thirdly, I wrote
> the driver to
> present the 256-colour linear framebuffer as eight mono
> planes, and the 
> transformation to and fro slows things down.
> 
>   (At the time, I had never seen a GEM driver where the
> number of colours
> wasn't 2^(number of planes). I have since seen two: the
> Trident 4-colour
> drivers require four planes for four colours, where you'd
> expect only two. It
> would be an interesting experiment to see how well GEM and
> its apps cope
> with a linear framebuffer; I know my DJGPP bindings wouldn't
> like it at
> all). 
>  
> > I'm, also, wondering why the GEM/3 _can_ support the
> higher colors but the =
> > later and, presumably, more modern GEM/4 and GEM/5 are
> not able to. Hmmm.
> 
>   You'll see that there is a 1024x768x256 driver for
> GEM/4 in pack 2. The
> reason it's there rather than in pack 1 is because Artline
> doesn't get on 
> very well with more than 16 colours.
> 
>   The reason I didn't do it for GEM/5 is that all the
> GEM/5 drivers I've
> done have been for 16-colour VGA-style hardware, since I
> only had a 
> 16-colour VGA driver to start from.
>  
> > When it says "VESA", that's like SciTech Software's
> VESA BIOS Extension (VB=
> > E) TSR or manufactuer's ROM based one?
> 
>   Anything that implements those VESA BIOS calls the
> driver wants 
> (INT 10/AX=4F02h to set the mode, INT 10/AX=4F01h to get
> information, and
> so on).
> 
> -- 
> John Elliott
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