Scripted objects/es

Introduction
Además de los tipos de objetos estándar, tales como anotaciones, mallas y objetos de pieza, FreeCAD también ofrece la estupenda posibilidad de construir objetos de archivos de guión hechos al 100% en Python, llamados Funcionalidades Python (Feature Python). Esos objetos se comportan exactamente como cualquier otro objeto de FreeCAD, y se guardar y restauran automáticamente al guardar o cargar archivos.

Debe comprenderse una particularidad, dichos objetos son guardados en archivos FcStd de FreeCAD con el módulo de Python cPickle. Este módulo devuelve un objeto de Python como una cadena de texto, permitiendo que se añada al guardado del archivo. En la carga, el módulo cPickle utiliza esa cadena de texto para recrear los objetos originales, proporcionándole acceso al código fuente que creó el objeto. Es decir que si guardas un objeto personalizado y lo abres en un ordenador en el que el código de Python que generó dicho objeto no está presente, el objeto no será recreado. Si distribuyes dichos objetos a otros usuarios, tendrás que distribuirlos junta al archivo de guión de Python que los crea.

Note: It is possible to pack python code inside a FreeCAD file using json serializing with an App::PropertyPythonObject, but that code can never directly be run, and therefore has little use for our purpose here.

Las Funcionalidades Python siguen las mismas reglas que todas las Funcionalidades de FreeCAD: se separan en las partes de App y GUI. La parte de App, el objeto documento, define la geometría de nuestro objeto, mientras que su parte GUI, el objeto proveedor de vistas, define el modo en que el objeto se dibujará en la pantalla. El objeto proveedor de vistas, como cualquier otra Funcionalidad de FreeCAD, sólo está disponible cuando se ejecuta FreeCAD en su propio GUI. Hay varias propiedades y métodos disponibles para construir tu objeto. Las propiedades tienen que ser de cualquiera de los tipos predefinidos de propiedades que ofrece FreeCAD, y aparecerá en la ventana de vista de propiedades, por lo que puede ser editado por el usuario. De esta manera, los objetos Funcionalidad Python son total y absolutamente paramétricos. Puedes definir las propiedades del objeto y de su ViewObject por separado.

Ejemplo básico
El ejemplo siguiente se puede encontrar en el archivo src/Mod/TemplatePyMod/FeaturePython.py, junto con varios otros ejemplos:

Things to note
If your object relies on being recomputed as soon as it is created, you must do this manually in the function as it is not called automatically. This example does not require it because the method of the  class has the same effect as the  function, but the examples below rely on being recomputed before anything is displayed in the 3D view. In the examples, this is done manually with but in more complex scenarios you need to decide where to recompute either the whole document or the FeaturePython object.

This example produces a number of exception stack traces in the report view window. This is because the method of the  class is called each time a property is added in. When the first one is added, the Width and Height properties don't exist yet and so the attempt to access them fails.

An explanation of and  is in the forum thread obj.Proxy.Type is a dict, not a string.

Available methods
See FeaturePython methods for the complete reference.

Propiedades disponibles
Las propiedades son las auténticas piedras de construcción de los objetos FeaturePython. A través de ellas, el usuario será capaz de interactuar y modificar su objeto. Después de crear un nuevo objeto FeaturePython en tu documento ( a=FreeCAD.ActiveDocument.addObject("App::FeaturePython","Box") ), puedes obtener una lista de las propiedades disponibles escribiendo:

Obtendrás una lista de propiedades disponibles:


 * App::PropertyAcceleration
 * App::PropertyAngle
 * App::PropertyArea
 * App::PropertyBool
 * App::PropertyBoolList
 * App::PropertyColor
 * App::PropertyColorList
 * App::PropertyDirection
 * App::PropertyDistance
 * App::PropertyEnumeration
 * App::PropertyExpressionEngine
 * App::PropertyFile
 * App::PropertyFileIncluded
 * App::PropertyFloat
 * App::PropertyFloatConstraint
 * App::PropertyFloatList
 * App::PropertyFont
 * App::PropertyForce
 * App::PropertyFrequency
 * App::PropertyInteger
 * App::PropertyIntegerConstraint
 * App::PropertyIntegerList
 * App::PropertyIntegerSet
 * App::PropertyLength
 * App::PropertyLink
 * App::PropertyLinkChild
 * App::PropertyLinkGlobal
 * App::PropertyLinkHidden
 * App::PropertyLinkList
 * App::PropertyLinkListChild
 * App::PropertyLinkListGlobal
 * App::PropertyLinkListHidden
 * App::PropertyLinkSub
 * App::PropertyLinkSubChild
 * App::PropertyLinkSubGlobal
 * App::PropertyLinkSubHidden
 * App::PropertyLinkSubList
 * App::PropertyLinkSubListChild
 * App::PropertyLinkSubListGlobal
 * App::PropertyLinkSubListHidden
 * App::PropertyMap
 * App::PropertyMaterial
 * App::PropertyMaterialList
 * App::PropertyMatrix
 * App::PropertyPath
 * App::PropertyPercent
 * App::PropertyPersistentObject
 * App::PropertyPlacement
 * App::PropertyPlacementLink
 * App::PropertyPlacementList
 * App::PropertyPosition
 * App::PropertyPrecision
 * App::PropertyPressure
 * App::PropertyPythonObject
 * App::PropertyQuantity
 * App::PropertyQuantityConstraint
 * App::PropertySpeed
 * App::PropertyString
 * App::PropertyStringList
 * App::PropertyUUID
 * App::PropertyVacuumPermittivity
 * App::PropertyVector
 * App::PropertyVectorDistance
 * App::PropertyVectorList
 * App::PropertyVolume
 * App::PropertyXLink
 * App::PropertyXLinkList
 * App::PropertyXLinkSub
 * App::PropertyXLinkSubList
 * Mesh::PropertyCurvatureList
 * Mesh::PropertyMeshKernel
 * Mesh::PropertyNormalList
 * Part::PropertyFilletEdges
 * Part::PropertyGeometryList
 * Part::PropertyPartShape
 * Part::PropertyShapeHistory
 * Path::PropertyPath
 * Path::PropertyTool
 * Path::PropertyTooltable
 * Sketcher::PropertyConstraintList
 * Spreadsheet::PropertyColumnWidths
 * Spreadsheet::PropertyRowHeights
 * Spreadsheet::PropertySheet
 * Spreadsheet::PropertySpreadsheetQuantity
 * TechDraw::PropertyCenterLineList
 * TechDraw::PropertyCosmeticEdgeList
 * TechDraw::PropertyCosmeticVertexList
 * TechDraw::PropertyGeomFormatList

Cuando se añaden propiedades a tus objetos personalizados, ten en cuenta esto:
 * No utilices caracteres "<" o ">" en las descripciones de las propiedades (eso rompería las partes de xml en el archivo .fcstd)
 * Las propiedades se almacenan alfabéticamente en un archivo .fcstd. Si tienes una forma en tus propiedades, cualquier propiedad cuyo nombre va después de "Shape" en orden alfabético, se cargará DESPUÉS de la forma, lo que puede causar un comportamiento extraño.

A complete list of property attributes can be seen in the PropertyStandard C++ header file. For instance, if you want to allow the user to enter only a limited range of values (e.g. using PropertyIntegerConstraint), in Python you will assign a tuple containing not only the property value, but also the lower and upper limit as well as the stepsize, as below:

Property Type
By default the properties can be updated. It is possible to make the properties read-only, for instance in the case one wants to show the result of a method. It is also possible to hide the property. The property type can be set using:

where mode is a short int that can be set to: 0 -- default mode, read and write 1 -- read-only 2 -- hidden

The EditorModes are not set at FreeCAD file reload. This could to be done by the __setstate__ function. See http://forum.freecadweb.org/viewtopic.php?f=18&t=13460&start=10#p108072. By using the setEditorMode the properties are only read only in PropertyEditor. They could still be changed from python. To really make them read only the setting has to be passed directly inside the addProperty function. See http://forum.freecadweb.org/viewtopic.php?f=18&t=13460&start=20#p109709 for an example.

Using the direct setting in the addProperty function, you also have more possibilities. In particular, an interesting one is mark a property as an output property. This way FreeCAD won't mark the feature as touched when changing it (so no need to recompute).

Example of output property (see also https://forum.freecadweb.org/viewtopic.php?t=24928):

The property types that can be set at last parameter of the addProperty function are: 0 -- Prop_None, No special property type 1 -- Prop_ReadOnly, Property is read-only in the editor 2 -- Prop_Transient, Property won't be saved to file 4 -- Prop_Hidden, Property won't appear in the editor 8 -- Prop_Output, Modified property doesn't touch its parent container 16 -- Prop_NoRecompute, Modified property doesn't touch its container for recompute 32 -- Prop_NoPersist, Property won't be saved to file at all

You can find these different property types defined in the source code C++ header for PropertyContainer.

Otro ejemplo más complejo
En este ejemplo se hace uso del Módulo de Pieza para crear un octaedro, a continuación, se crea su representación Coin con Pivy.

Lo primero es el propio objeto del documento:

después, conseguimos el objeto proveedor de vista, responsable de mostrar el objeto en la escena 3D:

Por último, una vez que nuestro objeto y su viewobject están definidos, sólo nos falta invocarlos:

Haciendo objetos seleccionables
Si deseas hacer tu objeto seleccionable, o al menos parte de el, haciendo clic sobre el en el visor, debes incluir su geometría Coin dentro de un nodo SoFCSelection. Si el objeto tiene una representación compleja, con widgets, anotaciones, etc, puede que desees incluir sólo una parte de el en un SoFCSelection. Todo lo que es un SoFCSelection es constantemente explorado por FreeCAD para detectar selección/preselección, por lo que tiene sentido evitar sobrecargalo con innecesarias exploraciones. Esto es lo que se haría para incluir un self.face en el ejemplo anterior:

Once the parts of the scenegraph that are to be selectable are inside SoFCSelection nodes, you then need to provide two methods to handle the selection path. The selection path can take the form of a string giving the names of each element in the path, or of an array of scenegraph objects. The two methods you provide are, which converts from a string path to an array of scenegraph objects, and , which takes an element which has been clicked on in the scenegraph and returns its string name (note, not its string path).

Here is the molecule example above, adapted to make the elements of the molecule selectable:

Trabajar con formas simples
Si tu objeto paramétrico saca simplemente una forma, no es necesario utilizar un objeto proveedor de vista. La forma se mostrará en la representación de formas de FreeCAD:

Same code with use ViewProviderLine

Scenegraph Structure
You may have noticed that the examples above construct their scenegraphs in slightly different ways. Some use while others use.

Each feature in a FreeCAD document is based the following scenegraph structure:

The displays only one of its children, depending on which display mode is selection in FreeCAD.

The examples which use are constructing their scenegraphs solely out of coin3d scenegraph elements. Under the covers, adds a new child to the ; the name of that node will match the display mode it was passed.

The examples which use also construct part of their geometry using functions from the Part workbench, such as. This constructs the different display mode scenegraphs under the ; when we later come to add coin3d elements to the scenegraph, we need to add them to the existing display mode scenegraphs using rather than creating a new child of the.

When using to add geometry to the scenegraph, each display mode should have its own node which is passed to ; don't reuse the same node for this. Doing so will confuse the selection mechanism. It's okay if each display mode's node has the same geometry nodes added below it, just the root of each display mode needs to be distinct.

Here is the above molecule example, adapted to be drawn only with Coin3D scenegraph objects instead of using objects from the Part workbench:

Part Design scripted objects
When making scripted objects in Part Design the process is similar to the scripted objects discussed above, but with a few additional considerations. We must handle 2 shape properties, one for the shape we see in the 3D view and another for the shape used by the pattern tools, such as polar pattern features. The object shapes also needs to be fused to any existing material already in the Body (or cut from it in the case of Subtractive features). And we must account for the placement and attachment of our objects a little bit differently.

Part Design scripted solid object features should be based on either PartDesign::FeaturePython, PartDesign::FeatureAdditivePython, or PartDesign::FeatureSubtractivePython rather than Part::FeaturePython. Only the Additive and Subtractive variants can be used in pattern features, and if based on Part::FeaturePython when the user drops the object into a Part Design Body it becomes a BaseFeature rather than being treated by the Body as a native Part Design object. Note: all of these are expected to be solids, so if you are making a non-solid feature it should be based on Part::FeaturePython or else the next feature in the tree will attempt to fuse to as a solid and it will fail.

Here is a simple example of making a Tube primitive, similar to the Tube primitive in Part Workbench except this one will be a Part Design solid feature object. For this we will 2 separate files: pdtube.FCMacro and pdtube.py. The .FCMacro file will be executed by the user to create the object. The .py file will hold the class definitions, imported by the .FCMacro. The reason for doing it this way is to maintain the parametric nature of the object after restarting FreeCAD and opening a document containing one of our Tubes.

First, the class definition file:

And now the macro file to create the object:



Additional pages:
 * Scripted objects saving attributes
 * Scripted objects migration
 * Scripted objects with attachment
 * Viewproviders

Interesting forum threads about scripted objects:


 * Python object attributes lost at load
 * New FeaturePython is grey
 * Explanation on __getstate__ and __setstate__, official documentation
 * Eigenmode frequency always 0?
 * how to implement python feature's setEdit properly?

In addition to the examples presented here have a look at FreeCAD source code src/Mod/TemplatePyMod/FeaturePython.py for more examples.