Pivy/fr

Pivy est une bibliothèque de codes qui sert de passerelle entre Python et Coin3d, la bibliothèque 3D de rendu graphique utilisé par FreeCAD. Lors de l'importation dans l'interpréteur Python, Pivy permet de dialoguer immédiatement avec les procédures de Coin3d, tels que les vue3D, ou même d'en créer de nouvelles.
Pivy est inclus d'origine dans l'installation FreeCAD.

La bibliothèque d'outils est divisée en plusieurs parties,

• coin: pour manipuler formes graphiques (projet) et gérer le système graphique (GUI), tels que plusieurs fenêtres ou, dans notre cas,
• qt  : pour les interfaces.
  

Ces modules sont aussi accessibles à pivy, s'ils sont présents sur le système bien sûr.
Le module coin est toujours présent, et de toute façon c'est lui que nous allons utiliser, nous n'aurons pas besoin de nous occuper de l'affichage 3D dans une interface, FreeCAD s'en occupe lui-même.
Tout ce que nous aurons à faire, c'est:

 from pivy import coin

Accéder et modifier une scène graphique

Nous avons vu dans la page Scenegraph comment coin organise une scène. Tout ce qui est affiché en 3D dans FreeCAD est construit et géré par coin.
Nous avons une racine, et tous les objets sur l'écran sont ses enfants, reliés par des nodes (noeuds). Les enfants aussi peuvent avoir une descendance.

FreeCAD has an easy way to access the root node of a 3D view scenegraph:

 sg = FreeCADGui.ActiveDocument.ActiveView.getSceneGraph()
 print sg

This will return the root node:

 <pivy.coin.SoSelection; proxy of <Swig Object of type 'SoSelection *' at 0x360cb60> >

We can inspect the immediate children of our scene:

 for node in sg.getChildren():
     print node

Some of those nodes, such as SoSeparators or SoGroups, can have children themselves. The complete list of the available coin objects can be found in the official coin documentation.

Let's try to add something to our scenegraph now. We'll add a nice red cube:

 col = coin.SoBaseColor()
 col.rgb=(1,0,0)
 cub = coin.SoCube()
 myCustomNode = coin.SoSeparator()
 myCustomNode.addChild(col)
 myCustomNode.addChild(cub)
 sg.addChild(myCustomNode)

and here is our (nice) red cube. Now, let's try this:

 col.rgb=(1,1,0)

See? everything is still accessible and modifiable on-the-fly. No need to recompute or redraw anything, coin takes care of everything. You can add stuff to your scenegraph, change properties, hide stuff, show temporary objects, anything. Of course, this only concerns the display in the 3D view. That display gets recomputed by FreeCAD on file open, and when an object needs recomputing. So, if you change the aspect of an existing FreeCAD object, those changes will be lost if the object gets recomputed or when you reopen the file.

A key to work with scenegraphs in your scripts is to be able to access certain properties of the nodes you added when needed. For example, if we wanted to move our cube, we would have added a SoTranslation node to our custom node, and it would have looked like this:

 col = coin.SoBaseColor()
 col.rgb=(1,0,0)
 trans = coin.SoTranslation()
 trans.translation.setValue([0,0,0])
 cub = coin.SoCube()
 myCustomNode = coin.SoSeparator()
 myCustomNode.addChild(col)
 mtCustomNode.addChild(trans)
 myCustomNode.addChild(cub)
 sg.addChild(myCustomNode)

Remember that in an openInventor scenegraph, the order is important. A node affects what comes next, so you can say something like: color red, cube, color yellow, sphere, and you will get a red cube and a yellow sphere. If we added the translation now to our existing custom node, it would come after the cube, and not affect it. If we had inserted it when creating it, like here above, we could now do:

 trans.translation.setValue([2,0,0])

And our cube would jump 2 units to the right. Finally, removing something is done with:

 sg.removeChild(myCustomNode)

Using callback mechanisms

A callback mechanism is a system that permits a library that you are using, such as our coin library, to call you back, that is, to call a certain function from your currently running python object. This is extremely useful, because that way coin can notify you if some specific event occurs in the scene. Coin can watch very different things, such as mouse position, clicks of a mouse button, keyboard keys being pressed, and many other things.

FreeCAD features an easy way to use such callbacks:

 class ButtonTest:
   def __init__(self):
     self.view = FreeCADGui.ActiveDocument.ActiveView
     self.callback = self.view.addEventCallbackPivy(SoMouseButtonEvent.getClassTypeId(),self.getMouseClick) 
   def getMouseClick(self,event_cb):
     event = event_cb.getEvent()
     if event.getState() == SoMouseButtonEvent.DOWN:
       print "Alert!!! A mouse button has been improperly clicked!!!"
       self.view.removeEventCallbackSWIG(SoMouseButtonEvent.getClassTypeId(),self.callback) 
 
 ButtonTest()

The callback has to be initiated from an object, because that object must still be running when the callback will occur. See also a complete list of possible events and their parameters, or the official coin documentation.

Documentation

Unfortunately pivy itself still doesn't have a proper documentation, but since it is an accurate translation of coin, you can safely use the coin documentation as reference, and use python style instead of c++ style (for example SoFile::getClassTypeId() would in pivy be SoFile.getClassId())

Scenegraph

PyQt

Index