Re: 16bpp graphics modes on old iMac, what is the MSB function?

larwe_at_larwe.com
Date: 06/01/05 

Date: 31 May 2005 19:05:16 -0700

Hi Tom,

Tom Stiller wrote:

> > Is there some special function assigned to the MSB of video memory in a
> > Mac running at "thousands" of colors, specifically a 16bpp mode on the
> > kernel framebuffer device?
>
> IIRC, the 2^15 bit was an alpha plane overlay bit. I think there's
> something wrong with your mapping. It makes no sense to have more bits
> representing blue than representing red.

I did post a reply saying I agree it makes no sense, but I'd verified
it experimentally. Well, that turns out to be a lie. In fact the mode
that the normal console runs in is utterly beyond weird. The color
components are in basically the right positions, but it's as if the DAC
is still in a palettized mode.

If I execute X & sleep 10 ; ./myapp then the graphics appear totally
normal.

It's really, really bizarre. Any thoughts?