[NBLUG/talk] Direct Render Support

[thiessen at sonic.net]

Yep, what's going on is that more than just a framebuffer representation
of the screen is being stored in that memory.  In my (admittedly limited)
understanding, with 3D enabled, the graphics card is using the memory to
do the following:

(1) Store the framebuffer representation of the screen.  At 4 bytes per
    pixel that's a fixed 4 * 1024 * 768 = 3145728  (3 megabytes) of memory.
(2) Temporarily store and process the 3-dimensional representation of
    3D objects on the screen.  This can suck up a LOT of memory.

This isn't even taking into account double-buffering, which I believe is
done in the card's memory, although I'm not sure.  (Please, anyone,
jump in and correct me if I'm wrong.)  This would double the memory
requirements for just having a framebuffer running.

Glad to hear you have 3D working, though.  And I've never been able to
see much difference between 16-bits and 24-bits on most laptop LCDs, anyways.

Congrats on joining the linux crowd!

Justin


> Just the same, at 32 bits it's only an even 3 megs,
> which still isn't 8, though you're probably right
> about there being other things to store in VRAM.  It'd
> be interesting to find out exactly what the
> composition of the RAM is right now.  Either way... IT
> WORKS! ^_^
> My display has exactly 1024x768 pixels, and it's
> driving me crazy that it doesn't have 1280, but I keep
> telling myself: you got what you paid for, don't
> bitch.
> Anyway, thanks for the helpful comments,
> Stephen
>
>
> --- Bill Kendrick <nbs at sonic.net> wrote:
>
>> (Jumping in here, apologies)
>>
>> On Thu, Nov 10, 2005 at 08:18:30PM -0800, Stephen
>> Cilley wrote:
>> > Ok, I went onto IRC today I got this all squared
>> away.
>> > It seems that 1024x768 at 24 bit pixel depth is
>> just
>> > too much for the IBM T22 (s3 Savage IX) as it has
>> only
>> > 8 megs of VRAM.  I'm not sure how that math works
>> out
>> > (1024x768 [res] X 24 [pixel depth] = 18874368
>> [total
>> > bits] / 8 = 2359296 [total bytes] / 1024 = 2304
>> [total
>> > KB] so like 2.25 megs...
>>
>> Dunno the details of the s3 chipset, but typically
>> computers
>> like working with even numbers, so often 24bpp ends
>> up requiring
>> 32 bits per pixel.  8 just go unused.  (The even
>> number her being
>> the number of Bytes per pixel... 4 instead of 3.)
>>
>> Backing store and 3D texture space may also be
>> considerations.
>>
>> Also, though, as a laptop, can your _display_ pump
>> out 1024x768?
>> If it doesn't have more physical pixels than that,
>> it probably
>> cannot. :)
>>
>> --
>> -bill!
>> bill at newbreedsoftware.com
>> http://www.newbreedsoftware.com/
>>
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