Re: CG14 and 16bit colour

[Michael <macallan1888%gmail.com@localhost>]

Hello,

On Wed, 24 Apr 2024 10:10:18 -0500
Bob Breuer <bbreuer711%gmail.com@localhost> wrote:

> 16-bit mode can go up to 1920x1080 even with only 4MB of VRAM,
> otherwise you need 8MB for the 24-bit mode.
> 
> While the CG14 can be abused to enable 16-bit modes, its native
> support is only for 8-bit and 24-bit, and also simultaneous 8 and 24
> on a per pixel basis.  The XLUT selects the color depth and which CLUT
> to use.  To get 16-bit, you need to use 2 of the CLUTs, one for each
> byte, then alpha blend them together, and use the DAC gamma table to
> scale back up.  Because the CLUTs are used, you can freely choose from
> any of 555, 565, RGB, BGR, or any other combination that fits into 16
> bits.  It's been a while since I experimented with this, but I can
> give more details if you want.

Hmm, in 8bit mode the cg14 still sends RGB data to the DAC, using its
own LUT. What exactly does it send in 16bit mode? If it's just raw
pixel data, what keeps us from just putting the DAC into RGB555 mode?

That being said, I haven't found much on how exactly the XLUT works so
my drivers just zero it and cross fingers. 

have fun
Michael