Re: How are 565 textures generated?

The texture could be dithered. I've seen my 888 textures dithered to 565 
on rage128 cards on macosx.

- Ray

Stephen J Baker wrote:
> If I create a texture with an external format that is 8+8+8 bit RGB,
> and an internal format of 5+6+5 RGB, how is the data converted by
> glTexImage2D ?
> 
> Are the least significant bits dropped, rounded or something else?
> 
> It *looks* like (at least on nVidia 6800 on their latest Linux drivers)
> they are doing something other than just truncating the LSbits.
> 
> I have two textures that don't match - one of which has been converted
> to 5/6/5 in software (by just truncating bits) - the other has been
> converted by the driver.  The path to this point is pretty convoluted
> and it's *possible* that there is some other cause - but I'd like to
> eliminate this cause if possible.
> 
> It seems that if the driver rounded the data then there would be a problem
> with numbers like 0xFF being rounded up to 0x100 and overflowing. That's
> what made me assume they'd be truncating it.
> 
> I also wonder what (if any) things are done to keep the extra bit of
> green precision from generating magenta/green tints to otherwise grey
> areas of the image.
> 
> -----------------------------------------------------------------------
> The second law of Frisbee throwing states: "Never precede any maneuver
> by a comment more predictive than "Watch this!"...it turns out that
> this also applies to writing Fragment Shaders.
> -----------------------------------------------------------------------
> Steve Baker                      (817)619-2657 (Vox/Vox-Mail)
> L3Com/Link Simulation & Training (817)619-2466 (Fax)
> Work: [email protected]           http://www.link.com
> Home: [email protected]       http://www.sjbaker.org
> 
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----- 
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-- 
Author: Ray Ratelis
  INET: [email protected]

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