Assigning a material without an appearance reset the appearance to the
default appearance.
There were two main problems. One was the comparison function for
App::Material objects. It would return false when the UUID or MatType
values were different although there are many circumstances where this
could be true and the appearance be the same. It also incorrectly
compared the imagePath.
The second problem was the logic for detecting if an object has already
been assigned an appearance by assigning a material or manually setting
the appearance. If assigned a material, the appearance should update but
not if it has been set manually. This logic has been corrected.
Every basic data type is stored in Base module, color is standing out as
one that does not. Moving it to Base opens possibilities to integrate it
better with the rest of FreeCAD.
Improves the use of the ShapeAppearance property for the Part workbench.
removes DiffuseColor property
adds Python compatibility using custom attributes
transitions DiffuseColor to ShapeAppearance on open
Improved UI elements for setting object appearance, and appearance per face
Lays the foundation for future texture support
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.
This patch includes the actual implementation of Link, which is
implemented as an extension named LinkBaseExtension in App namespace,
and a full view provider ViewProviderLink in Gui. The reason of not
using ViewProviderExtension is because it need full control when
display, not just extending existing functionalities.
Please see [here](https://git.io/fjPue) for more details of the
implementation.
This patch also includes a set of link manipulation commands, and a
task panel for overriding geometry element colors.
