RE: Best Video Card

["Mike A. Harris" <mharris redhat com>]

On Thu, 7 Feb 2002, Peter Petrakis wrote:

>Date: Thu, 7 Feb 2002 16:21:36 -0500
>From: Peter Petrakis <voodoo@alphadriven.org>
>To: axp-list@redhat.com
>Content-Type: text/plain;
>	charset="iso-8859-15"
>List-Id: Linux and Red Hat on Alpha processors <axp-list.redhat.com>
>Subject: RE: Best Video Card
>
>> About the only caveat that I can think of for the voodoo3 (as I use it 
>> myself) is the
>> hardware limitation of only supportting DRI in 16bpp mode
>
>That's a good point. I forgot about that. Also in normal
>X it only allows 24bpp mode max, No 32bpp. No big deal. 

Just some clarification info on 32bpp and XFree86.  32bpp color
depth simply doesn't exist in any hardware. What people generally
refer to as 32bpp is actually 24bit color packed into 32bits of
space.  There is no 32bit color mode, however XFree86 3.3.6, and
other operating systems such as Windows have confused this for 
quite some time.

There are two separate concepts withr espect to pixels, color 
depth, which is the number of bits actually used to represent 
color in a pixel, and "bits per pixel" which is the number of 
bits of video memory a given pixel takes up.

XFree refers to the color bits as "depth" and the bits per pixel
stored in memory as "framebuffer bits per pixel" or "fbbpp".
  
Normally you never supply nor need to supply XFree86 the fbbpp
value, as it determines that itself in the driver.  When you
select a particular color depth such as 8/15/16/24, the driver
knows to use a fbbpp value of 6/16/16/32 respectively.

32fbbpp pixel storage is the most efficient way of blitting
pixels to video memory, so all of the drivers default to using
32fbbpp whenever a 24 bit depth is selected unless the hardware
doesn't support it at all, or the driver hasn't implemented it
yet.  So when you choose Depth 24 in XFree86 4, you get 24 bit
color in a 32bpp framebuffer.  Both XFree86 3.3.6 and Microsoft
Windows refer to this as "32bpp", which is quite misleading.

In some cases you might want to override XFree86's fbbpp value to 
force it to 24fbbpp, for example if the resolution you choose 
doesn't fit in video RAM with 24/32, you may force 24/24 to 
reclaim 1/4 of the memory used.  There may be other reasons to 
override the default 32fbbpp as well.

Just rest assured, when you choose Depth 24 in XFree86, you are 
getting what other OS's call 32bpp - unless of course as I 
stated earlier, your hardware doesn't support it.  If in doubt, 
examine the XFree86 log file, it details what depth and fbbpp are 
being used.


>> As for Radion, can't comment, I can only find the card in AGP format 8/
> 
>Plenty of those on pw as well, search for "radeon pci" .

I'd like to pick one of those up, to try and get DRI working on 
x86, as it only works on axp currently.  ;o)

Hope my above info was helpful guys, good luck with your video 
hardware, and take care.

TTYL


-- 
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