I’m
not sure what CAV is. I’m currently using Matt Lind suggestion of using the
mib_bump_basis() function from the basetexgen.c
example
and it seems to be working well so far. But I am curious about that Tangent
and CAV technique. Could you elaborate more on it please? Do you think it
would be faster to process with your technique? What I also like about Lind’s
suggestion versus yours is that you don’t need to create a Tangent operator so
it’s a few less steps to do for the users but if it can accelerate the
calculations, maybe I’ll use yours instead. But if you could please elaborate
a bit more, it would be greatly
appreciated.
Thanks.
-----Original
Message-----
From:
owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM]On Behalf Of Halfdan
Ingvarsson
Sent: Tuesday,
February 28, 2006 2:38 PM
To:
XSI(at)Softimage.COM
Subject:
RE: passing U and V vectors to mental ray
state->derivs will
be filled in for parametric surfaces since derviatives are easy to derive from
those (pun intended).
For
polymeshes, there are no well-defined derivatives, since the surface is not
continuous. It is possible to provide derivatives for polygon meshes but we
don't since not everyone agrees what the best way of computing them
is.
There's
a Tangent operator in XSI (Property->Tangent) that you can apply to a
texture projection (which provides UV direction) and a CAV (which
receives the tangents). You can then add a texturespace parameter to a
shader that selects a CAV, which will then get added as a texture space to the
polymesh object and you can get the tangents from that.
-
½
-----Original
Message-----
From:
owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM]On Behalf Of Mathieu Leclaire
Sent: Tuesday, 28 February, 2006
14:30
To:
XSI(at)Softimage.COM
Subject:
RE: passing U and V vectors to mental ray
I’m
not sure that’s the info I’m looking for. First off, won’t the u and v vectors
change depending on the texture space selected? state->derivs is not
dependant of the texture space and they always return me a null vector in all
the tests I’ve done. I looked at the doc and though that maybe
state->bump_x_list and state->bump_y_list could be what I was looking
for but they also always return me a null
vector.
-----Original
Message-----
From:
owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM]On Behalf Of Alan Jones
Sent: Tuesday, February 28, 2006 12:40
PM
To:
XSI(at)Softimage.COM
Subject:
Re: passing U and V vectors to mental ray
I'm not sure if XSI passes them to
mental ray, but you should check for a state->derivs (double check the
exact name in the docs though).
This would be the info you're after for
working in tangent space.
Cheers,
Alan.
On 2/28/06, Mathieu Leclaire <mleclair(at)hybride.com>
wrote:
Hi,
I've been looking at
the D3 normal map source code and spdl and I've seen him accessing those
vectors from the parameters:
miVector
u; /* tangent from bump
basis */
miVector
v; /* binormal from bump
basis */
…Which I'm guessing,
and please correct me if I'm wrong, would represent the direction of the Us
and the Vs so we can determine the orientation of the texture at that point
right? So basically, if you would sample a point on the same triangle but a
little farther in the direction of the u vector then your UV from that new
point would have a U value higher then the one from the original sample… I
assume that's what it represents.
Anyway, D3 uses
those u and v vectors to transform the vectors to UV space or from UV space by
putting them in a matrix along with the surface normal before calling a
mi_vector_transform.
I can find a lot of
great use to those u and v vectors and create cool shaders but my attempt to
access those vectors through the spdl have so far failed miserably. I'm just
not yet comfortable with spdls and D3 links a few of them through the
phenomenon section like this:
phenomenon
"d3_normalmap_gen_declare"
{
Name = "d3_normalmap_gen";
Use = texture;
Version = 1;
Node "basis"
= guid "{811FFAA5-2A42-47DF-B767-8DAEB5993E9C}";
Node
"nmapgen" = guid
"{9B4BC656-96D1-4F3A-AC2F-2172A5D406A6}";
Connection
"basis::ntex"
= interface "tspace_id";
Connection "basis::project" =
interface "project";
Connection
"nmapgen::u"
= "basis::u";
Connection
"nmapgen::v"
= "basis::v";
Connection
"nmapgen::type" =
interface "type";
Connection "nmapgen::objects" = interface
"objects";
Connection
root
= "nmapgen";
}
…Where nmapgen is
linked through another spdl that contains the u and v vectors parameters. I'm
just all confused how it all works here. Can't I put all this in the same spdl
instead of having 2 spdls to install? Can anyone just explain to me how to
build my shaders spdl so that the user can chose a texture space and where
mental ray will be able to extract the u and v vectors? I want my shader to
work whether D3 is installed or not. Can anyone explain all this to me
please?
Thanks!
Mathieu
Leclaire
R&D
Programmer
Hybride
Technologies
