Sorry - please change the u_factor declaration to -1 to see the bug.  I
accidentally sent out the file where things were set to behave correctly.

I'm attaching a copy of the POV file I originally meant to send.

JP

"John Pallett" <joh### [at] chiefarchitectcom> wrote in message
news:3d1cd210@news.povray.org...
> Hi guys -
>
> A curious one for you here, I'm running into problems using bump maps when
> I'm using a uv_mapping.
>
> The problem is that the bump-map normals seem to be dependent upon the
> direction of the u/v vectors - for example, a triangle with UV coordinates
> <1,0> <0,0> <0,1> will give different results than a triangle with UV
> coordinates <-1,0> <0,0> <0,1> even though the bump map is symmetrical in
> the U and V dimensions, and the triangle vertices are exactly the same and
> in the
> same order.
>
> It almost seems like the way that the bump map affects the surface normal
is
> dependent upon the U and V 'direction' of the bump map.  Note that the
> physical triangle
> normal is not affected by the UV coordinates - just the normal that is
> generated
> by the bump-map.
>
> See the attached POV file - note that in the U-axis (along the wall) the
> bump-map behaves one way, and in the
> V-axis (up and down) it behaves in another.  Set the declaration of
> "u_factor" to 1 to see the desired result where
> the bump-map behaves appropriately.
>
> Is this a bug?  I would expect U/V coordinates to simply define source
> points on a bump-map or
> texture.  Why does it affect the normal?
>
> John Pallett
>
>
>

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Attachments:
Download 'bump_inversion.pov.txt' (2 KB) Download 'bump_pyramids.jpg' (3 KB)

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