Re: 8-bit alpha in 32-bit frame-buffer?????

[Nick Hill <nikhilwiz@yahoo.com>]

I've had it! are all the gurus on the list asleep or
something? When i joined this list, there were a *lot*
of gurus around. looks like all of them have gone
away... :(

I know this list is for beginners, but this thread is
giving the wrong info to *all* of us.

Alpha channel is used for transparency. Not as a
"padding" byte! Alpha is used to indicate the degree
of transparency of a color, for blending purposes.

>   ----- Original Message ----- 
>   From: Tom.P.Monkish (aka Monkfish) 
>   32-bit video modes are the same as 24-bit video
> modes. So why do they exist? Simple: they're faster,
> because it's easier for the CPU to send out or read
> in 4 bytes (dwords) each time, instead of 3 bytes
> (read one word, than one byte). So think of the
> alpha byte as a padding byte - standard (without
> hardware acceleration) VESA modes don't use them for
> anything! Of course, they waste more memory.
> 

i'd sure like to know what u mean by "standard
(without acceleration)". u mean there are
"non-standard" VESA modes too? i thought VESA = Video
Enhanced *Standard* Architecture. This is the first
time i've heard that transfering *more* data is faster
than transferring less data.

>   Lets just say, that in 16-bit modes, there's no
> support for alpha channels, the obvious advantage is
> that they're faster - each pixel only uses 2 bytes.
> 15-bit color modes (not used anymore?) are ARGB,
> with one alpha bit, and 5 bits for each color
> (1555). Just like 32-bit modes, the

(1+5+5+5) != 15. so what gives?

>   padding bit isn't used.
> 

15-bit modes *dont* have an alpha channel!

> 
>   I think that the 3D 'alpha' acceleration features
> of modern cards do use the information stored in the
> alpha channel, but I'm not sure. What I do know, is
> that most cards don't mind what value the alpha
> channel is given (usually zero) and that you can use
> it however you wish.
> 

puhleez! alpha is used to do a lot of stuff!!!
ofcourse the card minds the alpha. for heaven's sake,
its used for most of the effects like anti-aliasing,
motion blurr (T-buffer in V5), and a horde of other
blending routines.

Sorry if this leads to a flame war, but i guess i just
couldn't take any longer, with most of the stuff on
this list being *very* counter productive...

Nikhil.

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