[osg-users] OBJ reader and Ns / shininess

David Spilling david.spilling at gmail.com
Fri Apr 8 01:53:15 PDT 2011

Dear Baker Searles (Bradley?),

Way back when I was looking at OBJ import, I found these useful:


but these are just repeats of what the wotsit.org information has.

Here Ns is described as up to 1000.

However exporters (and importers) do seem terribly inconsistent about how
they use some of these parameters. Plus the MTL file should state - but
rarely does - a particular lighting model via the illum parameters, which
should be - but isn't, from what I recall - picked up by OSG and be used,
e.g. via different shader sets.

I can't see why, from the illumination models, this would necessarily have
an upper bound; they are just floating point exponents after all. As an
aside, I think most of the models I have seen with any illum value specified
have illum=2.

Can you find out what the equation 3dsMax is using for specular, in terms of
how it is scaling it's 0-100 value? This should help determine whether an
upper bound is even necessary.

I think if you fix this for one flavour of OBJ exporter, then it will break
someone elses models. So perhaps add an option to clamp Ns to the importer
that you can pass in when you know you need it?

For what it's worth, I quite like the OBJ format for all its archaism since
its easily human readable and easily attackable with text parsers...

Hope that helps.

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