Fix reflectivity parameters parsing in loadOBJFile

[SergioRAgostinho]

There was a bug, attempting to make a reassignment to a reference, on the reflectivity parameters parsing stage.
I also added support to the "Tr" tag, used by meshlab, which apparently is simply the complement of the "d" dissolve parameter.

[stefanbuettner]

Hey Sérgio,

was this reassignment error a compilation error? 'Cause this rgb value is not used anywhere, is it?

Don't know anything about this Tr tag. Is there any documentation in Meshlab, which mtl-format it supports? Would be nice to have a link to the mtl-format specification PCL supports (or is working towards supporting) in the MTL reader documentation, wouldn't it.
Wikipedia links to this one, for example: http://paulbourke.net/dataformats/mtl/.

Cheers,
Stefan

[SergioRAgostinho]

was this reassignment error a compilation error? 'Cause this rgb value is not used anywhere, is it?

It was not a compilation error. Just the underlying logic was messed up. The rgb value is used here and here. I remember I bumped on this bug while working with a specific file, and noticed the material parameters were messed up.

Don't know anything about this Tr tag. Is there any documentation in Meshlab, which mtl-format it supports? Would be nice to have a link to the mtl-format specification PCL supports (or is working towards supporting) in the MTL reader documentation, wouldn't it.
Wikipedia links to this one, for example: http://paulbourke.net/dataformats/mtl/.

True. For the Tr tag I took the description from wikipedia, but there's no reference to an actual standard.

[stefanbuettner]

True, but don't these functions just fill that local rgb variable based on the contents of st? And afterwards rgbis not used anywhere else.

[SergioRAgostinho]

You're right. Let me have a look tonight to see if I find my offending case :)

[SergioRAgostinho]

Just figured out what we were overlooking in our discussion. So notice that in my fix, rgb is actually a pointer and depending on the material tag, it gets assigned a different address, e.g. to tex_Ka, tex_Kd or tex_Ks. Then in fillRGBfromXYZ and fillRGBfromRGB, rgb is passed by reference, so I'm actually changing tex_Ka, tex_Kd or tex_Ks, respectively.

[jspricke]

I will add some comments in line. As a side note, please put different fixes in separate commits, makes them easier to review ;).

[jspricke]

Must have been the weather conditions, all good. Thanks!