#!/usr/bin/env python
#
# This example introduces 3D widgets. 3D widgets take advantage of the
# event/observer design pattern introduced previously. They typically
# have a particular representation in the scene which can be interactively
# selected and manipulated using the mouse and keyboard. As the widgets
# are manipulated, they in turn invoke events such as StartInteractionEvent,
# InteractionEvent, and EndInteractionEvent which can be used to manipulate
# the scene that the widget is embedded in. 3D widgets work in the context
# of the event loop which was set up in the previous example.
#
# Note: there are more 3D widget examples in VTK/Examples/GUI/.
#

# First we import the VTK Python package that will make available all
# of the VTK commands to Python.
import vtk

# Next we create an instance of vtkConeSource and set some of its
# properties. The instance of vtkConeSource "cone" is part of a
# visualization pipeline (it is a source process object); it produces
# data (output type is vtkPolyData) which other filters may process.
cone = vtk.vtkConeSource()
cone.SetHeight(3.0)
cone.SetRadius(1.0)
cone.SetResolution(10)

# In this example we terminate the pipeline with a mapper process object.
# (Intermediate filters such as vtkShrinkPolyData could be inserted in
# between the source and the mapper.)  We create an instance of
# vtkPolyDataMapper to map the polygonal data into graphics primitives. We
# connect the output of the cone souece to the input of this mapper.
coneMapper = vtk.vtkPolyDataMapper()
coneMapper.SetInput(cone.GetOutput())

# Create an actor to represent the cone. The actor orchestrates rendering of
# the mapper's graphics primitives. An actor also refers to properties via a
# vtkProperty instance, and includes an internal transformation matrix. We
# set this actor's mapper to be coneMapper which we created above.
coneActor = vtk.vtkActor()
coneActor.SetMapper(coneMapper)

# Create the Renderer and assign actors to it. A renderer is like a
# viewport. It is part or all of a window on the screen and it is
# responsible for drawing the actors it has.  We also set the
# background color here.
ren1 = vtk.vtkRenderer()
ren1.AddActor(coneActor)
ren1.SetBackground(0.1, 0.2, 0.4)

# Finally we create the render window which will show up on the screen
# We put our renderer into the render window using AddRenderer. We
# also set the size to be 300 pixels by 300.
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren1)
renWin.SetSize(300, 300)

# The vtkRenderWindowInteractor class watches for events (e.g., keypress,
# mouse) in the vtkRenderWindow. These events are translated into
# event invocations that VTK understands (see VTK/Common/vtkCommand.h
# for all events that VTK processes). Then observers of these VTK
# events can process them as appropriate.
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)

# By default the vtkRenderWindowInteractor instantiates an instance
# of vtkInteractorStyle. vtkInteractorStyle translates a set of events
# it observes into operations on the camera, actors, and/or properties
# in the vtkRenderWindow associated with the vtkRenderWinodwInteractor. 
# Here we specify a particular interactor style.
style = vtk.vtkInteractorStyleTrackballCamera()
iren.SetInteractorStyle(style)


# Here we use a vtkBoxWidget to transform the underlying coneActor (by
# manipulating its transformation matrix). Many other types of widgets
# are available for use, see the documentation for more details.
#
# The SetInteractor method is how 3D widgets are associated with the render
# window interactor. Internally, SetInteractor sets up a bunch of callbacks
# using the Command/Observer mechanism (AddObserver()). The place factor 
# controls the initial size of the widget with respect to the bounding box
# of the input to the widget.
boxWidget = vtk.vtkBoxWidget()
boxWidget.SetInteractor(iren)
boxWidget.SetPlaceFactor(1.25)

# Place the interactor initially. The input to a 3D widget is used to
# initially position and scale the widget. The EndInteractionEvent is
# observed which invokes the SelectPolygons callback.
boxWidget.SetProp3D(coneActor)
boxWidget.PlaceWidget()

# Similar to Step2/Python/Cone2.py, we define a callback for
# interaction.  As can be seen the callback takes two arguments.  The
# first being the object that generates the event and the second
# argument the event name (which is a string).
def myCallback(widget, event_string):
    t = vtk.vtkTransform()
    boxWidget.GetTransform(t)
    boxWidget.GetProp3D().SetUserTransform(t)
        

# Now for every interaction event that is generated by the boxWidget,
# call our callback function.
boxWidget.AddObserver("InteractionEvent", myCallback)

# Normally the user presses the "i" key to bring a 3D widget to
# life. Here we will manually enable it so it appears with the cone.
boxWidget.On()

# Start the event loop.
iren.Initialize()
iren.Start()

# There is no explicit need to free any objects at this point.
# Once Python exits, memory is automatically freed.
