vtkSplineWidget

Section: Visualization Toolkit Widget Classes

Usage

This 3D widget defines a spline that can be interactively placed in a scene. The spline has handles, the number of which can be changed, plus it can be picked on the spline itself to translate or rotate it in the scene. A nice feature of the object is that the vtkSplineWidget, like any 3D widget, will work with the current interactor style. That is, if vtkSplineWidget does not handle an event, then all other registered observers (including the interactor style) have an opportunity to process the event. Otherwise, the vtkSplineWidget will terminate the processing of the event that it handles.

To use this object, just invoke SetInteractor() with the argument of the method a vtkRenderWindowInteractor. You may also wish to invoke "PlaceWidget()" to initially position the widget. The interactor will act normally until the "i" key (for "interactor") is pressed, at which point the vtkSplineWidget will appear. (See superclass documentation for information about changing this behavior.) Events that occur outside of the widget (i.e., no part of the widget is picked) are propagated to any other registered obsevers (such as the interaction style). Turn off the widget by pressing the "i" key again (or invoke the Off() method).

The button actions and key modifiers are as follows for controlling the widget: 1) left button down on and drag one of the spherical handles to change the shape of the spline: the handles act as "control points". 2) left button or middle button down on a line segment forming the spline allows uniform translation of the widget. 3) ctrl + middle button down on the widget enables spinning of the widget about its center. 4) right button down on the widget enables scaling of the widget. By moving the mouse "up" the render window the spline will be made bigger; by moving "down" the render window the widget will be made smaller. 5) ctrl key + right button down on any handle will erase it providing there will be two or more points remaining to form a spline. 6) shift key + right button down on any line segment will insert a handle onto the spline at the cursor position.

The vtkSplineWidget has several methods that can be used in conjunction with other VTK objects. The Set/GetResolution() methods control the number of subdivisions of the spline; the GetPolyData() method can be used to get the polygonal representation and can be used for things like seeding streamlines or probing other data sets. Typical usage of the widget is to make use of the StartInteractionEvent, InteractionEvent, and EndInteractionEvent events. The InteractionEvent is called on mouse motion; the other two events are called on button down and button up (either left or right button).

Some additional features of this class include the ability to control the properties of the widget. You can set the properties of the selected and unselected representations of the spline. For example, you can set the property for the handles and spline. In addition there are methods to constrain the spline so that it is aligned with a plane. Note that a simple ruler widget can be derived by setting the resolution to 1, the number of handles to 2, and calling the GetSummedLength method!

To create an instance of class vtkSplineWidget, simply invoke its constructor as follows

  obj = vtkSplineWidget

Methods

The class vtkSplineWidget has several methods that can be used. They are listed below. Note that the documentation is translated automatically from the VTK sources, and may not be completely intelligible. When in doubt, consult the VTK website. In the methods listed below, obj is an instance of the vtkSplineWidget class.