Re: [Algorithms] DotProduct3 bump-mapping question

[Scott B. <Scott@Mad-FX.com>]

Cool we seem to be on the same page. This clears things up nicely. I agree
there are many flavors in doing this and I'll sit down and think hard on
which will be better and which can eventually be done nicely with vertex
shaders.

> 3. Compute the uv gradient vectors for each triangle
> 4. Sum the gradients at each vertex for every triangle that shares it.
> (similar to calculating smooth normals)

Do any of the NVidia sample or others do this? That's exactly what I was
afraid I would have to do but I could never figure out if any of the samples
where doing it.

Thanks Even :)

----- Original Message -----
From: "Evan Hart" <eh...@at...>
To: <gda...@li...>
Sent: Monday, March 05, 2001 8:39 PM
Subject: RE: [Algorithms] DotProduct3 bump-mapping question


> Scott,
>
>   Generally the way you deal with the problems I think you are concerned
> about is by creating a tangent space across the surface. The tangent space
> allows the normal map to have +Z (or whatever your convention is) point
away
> from the surface. To calculate tangent space for an arbitrarily mapped
> surface do the following:
>
> 1. Create surface normals obeying any faceting rules.
> 2. Seperate the vertices such that each has unique tex coords and normal
> 3. Compute the uv gradient vectors for each triangle
> 4. Sum the gradients at each vertex for every triangle that shares it.
> (similar to calculating smooth normals)
> 5. Possibly ortho-normalize the bases (don't change normal)
>
> Now, you have a normal, tangent, and binormal. When you bump map transform
> the light vector at each vertex into the space defined by the normal,
> tangent, and binormal. This vector is then interpolated across the surface
> for the dp3 operation. You can use a cube map to deal with
denormalization.
>
> There are many flavors of this whole process, and I do not profess to be
an
> expert on all of them. One twist, is that you use the process above to
only
> create the tangent in the direction of positive U (or V) and then cross it
> with the normal to get the binormal.
>
> Finally, there is another uglier way to do this. If your texels are all
> unique, you can map them all to object space rather than mapping the light
> to surface space.
>
> Hope this helps.
>
> -Evan
>
> -----Original Message-----
> From: Scott Bean [mailto:Scott@Mad-FX.com]
> Sent: Monday, March 05, 2001 7:59 PM
> To: gda...@li...
> Subject: Re: [Algorithms] DotProduct3 bump-mapping question
>
>
> > yeah, but you have to remember, all these calculations are being done in
> > texture space.
>
> See akbar, unless I'm not following right, texture space is WARPED, if the
> geometry is complex and the UV wrap is warped and reversed and all weird,
> then there is no real texture space. And if you mean the light vector to
be
> rotated in the current vertice's UV coord. texture space, then how do you
do
> that...
>
> For example, would your bump mapping implementation work with a torus
object
> mapped properly and tiled say 8 times with a reversed(flip) wrap
addressing
> mode. See at each unit, the texture space is changed... this is what I'm
> having problems with...
>
>
>
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