Refactored code to support local and external material sources
This is the first PR in a series to support external modules. External
modules allow materials to be stored in external data sources such as
databases or web services. No new functionality is introduced in this
PR, rather it is a refactoring of code that will allow for changes to
be introduced in future PRs. Minor performance improvements have also
been made in the model and material managers.
The Python API has been enhanced for many data types to allow for
modification within Python.
Uses new material system for appearance
Each feature object now has a property called ShapeMaterial that
describes its physical properties. If it has a shape, it has a
material.
The ShapeColor attribute is replaced by a ShapeAppearance attribute.
This is a material list that describes all appearance properties, not
just diffuse color. As a list in can be used for all elements of a
shape, such as edges and faces.
A new widget is provided to allow the user to select materials in a
consistent fashion. It can also launch the material editor with its
more advanced capabilities.
