Hmm, that sounds plausible. I guess that's a not-unreasonable design
decision, even though I'd opt for elegance and uniformity (being a
Smalltalker, it's obvious that pure speed isn't my #1 priority ;-)
Thanks!
Josh
On Mon, Mar 28, 2005 at 12:11:50PM -0600, Keenan Crane wrote:
> I don't have a great answer, but here's my guess: the vertex program
> clamps color output by default because it doesn't know if there's a
> custom fragment program being run. If there's not, then by default the
> color would need to be clamped at each fragment, which would be a
> slower default behavior than clamping at the vertex stage and assuming
> interpolated values didn't need to be clamped. Though skimming through
> the Cg Tutorial it doesn't look like it talks about this issue.
>
> Keenan
>
> On Mar 28, 2005, at 9:06 AM, Joshua 'Schwa' Gargus wrote:
>
> >Hi,
> >
> >By trial and error, I determined that the COLOR output of
> >my vertex program was being clamped to the range [0,1].
> >I would have expected that the clamping would occur only
> >on the output of the fragment program. I worked around
> >this by storing the value in TEXCOORD0 instead.
> >
> >Where is this information documented? I couldn't find it
> >in the Cg Toolkit User's Manual.
> >
> >I don't like this behavior, it seems too much like magic.
> >I understand why the fragment color output needs to be
> >clamped, but it doesn't seem necessary for the vertex
> >color output.
> >
> >I think I read once that it is possible to create your own
> >custom semantics, but again I couldn't find this in the
> >User's Manual (maybe I read it in the Cg Tutorial book,
> >which I don't currently have access to). Is this true? If
> >I am imagining this, the rest of the paragraph does not
> >apply. Is it possible to create a custom semantic that
> >clamps the value passed from the vertex to the fragment
> >program? If not, this is an example of what I mean by magic:
> >an un-/poorly-documented exception to the core model of
> >the language/runtime that can only be achieved by hacking
> >the framework itself (not just by using the framework).
> >
> >Maybe I'm missing something obvious about why this clamping
> >behavior is intuitive and/or necessary. If so, please
> >enlighten me.
> >
> >Thank you,
> >Josh
> >
> >
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