ColladaConv : `-useMaterialId` let use `id=` for `.material.xml`

[SuperUserNameMan]

Regarding : https://github.com/horde3d/Horde3D/issues/193

Without this patch, ColladaConv will use the name attribute (if available) of each material to generate the .material.xml filenames.

The problem is that, sometimes, this material.name contains special reserved characters that will cause unexpected issues with some file-system, and renaming each material in the "DCC tool-chain" might be time consuming.

As the id attribute of each material follows the XML schema xs:ID rule, it should be safer to use it to make .material.xml filenames.

This patch adds a new -useMaterialId command line argument that tells to ColladaConv to use material.id instead of material.name.

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Rationalisation :

Ok, so according to Collada Spec 1.4 page 8.54 : the id attribute of <material> is of type xs:ID.

According to xml-schema : xs:ID is derived from xs:NCName.

According to xml-schema : the xs:NCName valid pattern is [\i-[:]][\c-[:]]*.

And according to this page:

• if pure ASCII, \i could translates to [_:A-Za-z] and \c could translates to [-._:A-Za-z0-9]
• the -[:] excludes : from the \i and \c classes of characters.

So, [\i-[:]][\c-[:]]* translates into english to :

• ONE valid unicode letter or _, followed by any number of unicode letters, digits, _ or - or .

So, if this is correct, using the id attribute of <material> to generate the .material.xml filenames is safer than using its name attribute.