==============================================================================
In the Layers implementation there are User Layers, which have no direct impact on visualisation,
and allow to group conceptually related geometry into logical entities, and Visual Layers, which
define how geometries are visualised (or even whether they are visualised or not).
For User Layers, SketchObject is responsible for the definition of the layers, and SketcherGeometryExtension
is responsible for indicating the User Layer to which a geometry belongs (via a LayerId field).
For Visual Layers, ViewProviderSketch is responsible for the definition of the visual layers, and
ViewProviderSketchGeometryExtension is responsible for indicating the visual layer to which a geometry belongs.
With this commit, ViewProviderSketchGeometryExtension:
- takes over the responsibility of carrying a visual layer Id.
- is extended to be persistent and serialise the Id.
- is extended to be accesible from Python.
=========================================================================================
- Long overdue refactor to avoid repetition during save/restore and copy.
- New interface to notify an extension when it is attached. It also enables the extension to gain
a pointer to the geometry container. This is intended to extend the functionality already existing
in Part::Geometry.
==================================================================
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
==========================================================
Previously for Weights, ViewProviderSketch used getScaleFactor. This caused that upon zoom change
the Weights would not increase progresively, rather the would grow on the next redraw. Additionally,
upon substantial zoom out, the poles would grow several times bigger than the B-Spline.
This commit uses a new geometry extension intended only for ViewProviderSketch, to store a geometry
specific representation scale factor. This is calculated as a function of the B-Spline length. The
extension does not serialise to disk. It is just intended for runtime.
Dragging from the edge when the radius is constrained gives a wrong cosmetic result, because the representation circle and the
real value of the weight are different (by a scale factor). This commit prevents dragging on the edge in the most representative
cases where the radius is constrained.
