 | | | dot product? | dot product? 2004-06-04 - By Rick Walia
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err sorry "θ" should be theta. Thought I was typing in html.
/R
Quoting Rick Walia <xsilist@(protected)>:
> I don't know if this will work but....
>
> Since the dot product function is busted in the Vector to Scalar node:
>
> How about getting a scalar share node in your render tree and for the Input
> param,
> set a scriptedOp. In your scriptedOp you can say, do your calculations for the
> dot product?
>
> You should be able to use the XSI Math functions for calculating the dot
> product.
> If that is broken too then you can always calculate it yourself:
> u � v = |u| |v| cos θ
>
> Where θ is the angle between the 2 vectors.
>
> Maybe?
>
> /R
>
> Quoting Guy Rabiller <guy@(protected)>:
>
> > It should also be noted that a normalized dot product is [-1...+1] range,
> > and if you want to see the full range of it you have to 'remap' the values
> > to [0-1] range or else you will see 'half' of the effect.
> > --
> > guy rabiller | 3d technical director @ LaMaison
> >
> >
> > -- -- Original Message -- --
> > From: "Matt Lind" <speye_21@(protected)>
> > To: <xsi@(protected)>
> > Sent: Friday, June 04, 2004 9:19 PM
> > Subject: RE: dot product?
> >
> >
> > > If the docs say 'output' shader, then it's a misprint. It should say
> > 'texture'
> > > shader as texture shaders are the only class of shader that can be
> > connected to
> > > almost any other type of shader in the rendertree. Output shaders are
> > only
> > > called after rendering has completed and generally only deal with the
> > image
> > > buffers and whatever 3d information may be hanging around in memory that
> > hasn't
> > > been flushed yet.
> > >
> > > As for the dot product, the vector_state node doesn't compute dot product
> > > correctly. What it computes, I don't know, but it certainly isn't the dot
> > > product. This bug has been around since version one unfortunately.
> > >
> > > However, even if the dot product were computed correctly, you might run
> > into a
> > > different problem which may be the cause of the constant red color - you
> > have to
> > > make sure all your input vectors are described in the same coordinate
> > space.
> > > Primary (eye) rays are usually described in internal space where as
> > geometry
> > > normals may sometimes be computed in object space. If a vector is coming
> > from
> > > the wrong coordinate space, there's a chance it's value doesn't change on
> > a
> > > per-ray basis because it's frame of reference is local the to component
> > your
> > > querying which is why you see the constant red. It shouldn't matter which
> > > coordinate space you choose to do the computations just as long all the
> > vectors
> > > are described in the same coordinate space.
> > >
> > >
> > > Matt
> > >
> > > -- ---- ---- ---- ---- ---- ---- ---
> > > Matt Lind
> > > Animator / Technical Director
> > > Softimage certified instructor:
> > > Softimage|3D
> > > Softimage|XSI
> > > Matt(at)Mantom.net
> > >
> > >
> > >
> > > dot product?
> > > Date : Fri, 04 Jun 2004 12:57:24 -0400
> > > To : XSI(at)Softimage.COM
> > > From : Sam Cuttriss <samc(at)quietman.net>
> > > Subject : dot product?
> > >
> > > hello, im trying to use the dot product "Vector math scalar" node in the
> > render
> > > tree.
> > > so i have an eyeray and a geometry normal vector state as inputs.
> > > the dot product is just driving a gradient mixer so i can see whats going
> > on,
> > > but im just getting constant red?
> > >
> > > the dot product help refers to vector output shaders (bumpmap generator
> > and
> > > Texture Space Controllers)
> > >
> > > are vector state shaders not output shaders?
> > > or is there something im doing wrong?
> > >
> > > i was expecting to see something similar to putting an incidence node
> > directly
> > > into the gradient mixer?
> > > thanks
> > > _sam
> > > ---
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> >
> >
> >
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>
>
>
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