Re: [Mesa3d-dev] higher bit depth support

[Brian P. <br...@va...>]

luc-eric rousseau wrote:
> 
> Hello,
> for research, I would like to modify Mesa to support 16 bit per channel
> texture, as well as a higher precision render buffers, either 16 bit or
> single-precision floating point.
> 
> The goal here is to use Mesa to render (non-interactivly) in software high
> precision 3D images made with 16 bit texture source, without loss of
> quality.  The current precision of the vertex coordinates is fine, it's the
> precision of the shading and the alpha blending that matters.  The rendered
> images are not meant for PC monitors (which are only 8 bit per channel max).
> 
> My question is: how much trouble would it be?  Of course, I've already
> looked at the source, but I would like to get an idea of how much of the
> code I would have to change, and if there are roadblocks I would hit.  I
> should also point out that i'm lazy :^)

Unfortunately, it will be a lot of work.

It's something that I've had in the back of my head for a couple
years now.  If you look in src/config.h and src/types.h you'll see
a #define for CHAN_BITS and a GLchan datatype.  The idea is that
you could #define CHAN_BITS to 16 and GLchan would become a GLushort
and all the internal pixel paths would have 16 bits of precision
per color channel.

Changing all occurances of GLubyte and the magic number 255 into
GLchan and (1 << CHAN_BITS) - 1 is a step in the right direction
but I'm sure there's many more issues to fix.  It would probably
require a line-by-line audit of the entire code base to get it done
properly.

-Brian