AbstractMaterialData is now just a typedef to MaterialData, with all
existing public APIs moved to (and marked as deprecated, if they don't
make sense anymore). The new class doesn't have a virtual destructor as
that's not the desired use anymore -- and AbstractImporter::material()
APIs will be returning an Optional instead of a Pointer, which means any
potential subclasses will be sliced away.
PhongMaterialData is reimplemented using the new key/value store,
with no own members anymore -- thus having the same size as
MaterialData, and safe to be casted from it to access the helper APIs.
Compared to previous AbstractMaterialData, which was always just a
single type, the new data can describe several different materials at
once. This is the case for example with glTF, where a material can be
metallic/roughness but also have an alternative description using
specular/glossiness.
Currently the usage is undocumented, but when everything is in place, if
a material advertises given type, it can be then cast to one of
its convenience subclasses.
Vladimír Vondruš