Understanding 24-bit mode.

I'm reading LaMothe's "Tricks.. Windows.. Gurus" book, but am having
trouble understanding 24-bit mode. I don't even think my video card
supports it (the demo he included the disc doesn't work), but I'd
still like to understand how this works.

In 24-bit mode, he writes the 3 bytes to the surface in BGR. Why does
he do this? Why isn't it RGB? In 32-bit mode the bytes are arranged
(A)RGB, and in 16-bit mode the bits are RGB, too. Why is 24-bit mode
so different?

It's the whole endian thing, isn't it? That confuses me, too.
Shouldn't all the modes then be in the same BGR order?

Will someone please explain this to me?

Hi Steven, cr88192, all,

Yes, it does seem very arbitrary. It all depends on how the hardware
maker engineered the card to read the data from video memory. Luckily, if
the hardware maker designed the card to be DX compliant then it is required
to expose its supported formats through the DX interface. See the SDK docs
or LaMothe on how to do this (if you don't already know).
--


Best wishes,
Allen

"cr88192" <cr88192@hotmail.com> wrote in message
news:vgtimd626qhg55@corp.supernews.com...
>
> "Steven" <windecks@hotmail.com> wrote in message
> news:ce9a7d65.0307101724.1eb77d69@posting.google.c om...
> > I'm reading LaMothe's "Tricks.. Windows.. Gurus" book, but am having
> > trouble understanding 24-bit mode. I don't even think my video card
> > supports it (the demo he included the disc doesn't work), but I'd
> > still like to understand how this works.
> >
> > In 24-bit mode, he writes the 3 bytes to the surface in BGR. Why does
> > he do this? Why isn't it RGB? In 32-bit mode the bytes are arranged
> > (A)RGB, and in 16-bit mode the bits are RGB, too. Why is 24-bit mode
> > so different?
> >
> > It's the whole endian thing, isn't it? That confuses me, too.
> > Shouldn't all the modes then be in the same BGR order?
> >
> > Will someone please explain this to me?
>
> it is just one of those arbitrary details I guess. a lot of formats are
like
> this, ie: some being RGBA, others being BGRA... with graphics formats
> another arbitrary detail is whether y is up or down, and with some formats
> there is a need to conditionally flip the image.
>
> many things in software are arbitarary.
>
>
>

>
> Yes, it does seem very arbitrary. It all depends on how the hardware
> maker engineered the card to read the data from video memory. Luckily, if
> the hardware maker designed the card to be DX compliant then it is
required
> to expose its supported formats through the DX interface. See the SDK
docs
> or LaMothe on how to do this (if you don't already know).

yes.

I don't really use directx though, I tend to do things through gl myself...