==================================================================
GeometryExtension was originally designed to be serializable (save/restore). However,
GeometryMigrationExtension and ViewProviderSketchGeometryExtension have demonstrated the
usefulness of runtime-only GeometryExtensions.
The problem with runtime-only extensions being of a serializable type (GeometryExtension before
this commit) arises when Part::Geometry is to serialize the extensions and serialise the number
of extensions the geometry has. If runtime-only GeometryExtensions do not save a tag, then the
restore mechanism will expect more extensions that are actually in the XML file.
This commit makes GeometryExtension by default not serializable and deriving directly from
Base::BaseClass. A new class GeometryPersistentExtension is created, deriving from GeometryExtension
to provide serialisation. All Extensions requiring serialization derive from GeometryPersistentExtension
and those not requiring it from GeometryExtension directly.
This commit adapts all extensions to the new situation:
Part: GeometryDefaultExtension
Part: GeometryMigrationExtension
Sketcher: ViewProvierSketchGeometryExtension
Sketcher: SketchGeometryExtension and ExternalGeometryExtension
========================================
This is a light-weight c++ only geometry extension to enable migration of information that was stored within
the Part WB and should be migrated to another WB (for example Sketcher WB)
It is designed so that a single extension can migrate different types of data (current and future).
When new data needs to be migrated, first a new enum bit is to be added to the class enum and new data members are to
be added to store the information within GeometryMigrationExtension class.
In the Restore() function restoring the data to be migrated, a GeometryMigrationExtension extension is added to the
geometry to be migrated with the data information and the corresponding enum bit set.
In the object to receive the migration data, onDocumentRestored() it is checked whether an extension of type
GeometryMigrationExtension is present, if yes, it is checked whether a bit used for migration is set and, if yes,
the data is retrieved and the GeometryMigrationExtension extension (preferably) removed from the Geometry object.
* Added Part::Feature::getTopoShape/getShape() function that can obtain
shape from any object with proper implementation of getSubObject(). It
can even construct compound from group object with proper implementation
of getSubObjects().
* Modified ViewProviderExt to work on any object, because it now obtain
the shape using Part::Feature::getShape()
* Modified various Part features to obtain base/tool shapes using
Part::getShape(), which allows them to be any type of object,
including Link and groups.
* Modified various Part command to relax type requirement on selected
objects.
* Add support of link and group to dimension, and add dimension refresh
command
* Support link and group in simple command command, and add a few more
copy command variations.
* Add special handling of 'Shape' attribute in PropertyContainerPy and
use Part::Feature::getShape() to return shape for any object without
Shape property. This allows many python feature work with any object
without modification.
* GeometrySurface/CurvePy, add convenience attribute 'Rotation'
* TopoShapePy:
* Extended support of sub shape attribute, e.g. Compound1, Solid2,
SubShape3 ('SubShape' is used to access child shape of a compound)
* makeWires(), new API to sort and return wires given a list of edges.
* transformed/translated/rotated/scaled(), return a new shape with
some transformation.
* findPlane(), find the plane of a planar shape
* isCoplanar(), check if two shape are coplanar
========================================
Generalisation of code for a default geometry extension in the form of a template.
Default geometry extensions provide a standard interface for an extension having a single stored value (e.g. one int or one string).
Python implementation must be provided separatedly.
