CallBack

Description¶

Demonstrate how to set up a callback with client data.¶

Getting the camera orientation after interacting with the image is used as an example.

We define a callback passing the active camera as client data and linking the callback to the EndInteractionEvent of the * vtkRenderWindowInteractor** class.

This allows us to get the camera orientation after we manipulate the image. We can then copy/paste this data as needed into our camera to set up a nice initial orientation as shown in the example.

To help orient the cone, we use a * vtkOrientationMarkerWidget and a * vtkOutlineFilter.

C++¶

There are two methodologies in C++.

Create a class that inherits from * vtkCallbackCommand** reimplementing Execute [vtkObject](http://www.vtk.org/doc/nightly/html/classvtkObject.html#details)* caller, unsigned long evId, void*) and setting pointers to any client and/or call data as needed. When the class is implemented, it becomes the callback function.
Create a function with this signature: void f [vtkObject](http://www.vtk.org/doc/nightly/html/classvtkObject.html#details)* caller, long unsigned int evId, void* clientData, void* callData) and, where needed, create a vtkCallbackCommand setting its callback to the function we have created.

The example demonstrates both approaches.

In the function PrintCameraOrientation note how we convert an array to a vector and get a comma-separated list.

Python¶

In Python the approach is even simpler. We simply define a function to use as the callback with this signature: def MyCallback(obj, ev):. Then, to pass client data to it, we simply do: MyCallback.myClientData = myClientData. This relies on the fact that Python functions are in fact objects and we are simply adding new attributes such as myClientData in this case.

Code¶

CallBack.py

#!/usr/bin/env python

"""
Demonstrate the use of a callback.

We define the callback as the function: GetOrientation(obj, ev) in this case,
 and then add new attributes to it, for example, the camera.
"""

import vtk


def main():
    colors = vtk.vtkNamedColors()

    # Create the Renderer, RenderWindow and RenderWindowInteractor.
    ren = vtk.vtkRenderer()
    renWin = vtk.vtkRenderWindow()
    renWin.AddRenderer(ren)
    iren = vtk.vtkRenderWindowInteractor()
    iren.SetRenderWindow(renWin)

    # Use a cone as a source.
    source = vtk.vtkConeSource()
    source.SetCenter(0, 0, 0)
    source.SetRadius(1)
    # Use the golden ratio for the height. Because we can!
    source.SetHeight(1.6180339887498948482)
    source.SetResolution(128)
    source.Update()

    # Pipeline
    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputConnection(source.GetOutputPort())
    actor = vtk.vtkActor()
    actor.SetMapper(mapper)
    actor.GetProperty().SetColor(colors.GetColor3d("peacock"))
    # Lighting
    actor.GetProperty().SetAmbient(0.3)
    actor.GetProperty().SetDiffuse(0.0)
    actor.GetProperty().SetSpecular(1.0)
    actor.GetProperty().SetSpecularPower(20.0)

    # Get an outline of the data set for context.
    outline = vtk.vtkOutlineFilter()
    outline.SetInputData(source.GetOutput())
    outlineMapper = vtk.vtkPolyDataMapper()
    outlineMapper.SetInputConnection(outline.GetOutputPort())
    outlineActor = vtk.vtkActor()
    outlineActor.GetProperty().SetColor(colors.GetColor3d("Black"))
    outlineActor.SetMapper(outlineMapper)

    # Add the actors to the renderer, set the background and size.
    ren.AddActor(actor)
    ren.AddActor(outlineActor)
    ren.SetBackground(colors.GetColor3d("AliceBlue"))
    renWin.SetSize(512, 512)

    # Set up a nice camera position.
    camera = vtk.vtkCamera()
    camera.SetPosition(4.6, -2.0, 3.8)
    camera.SetFocalPoint(0.0, 0.0, 0.0)
    camera.SetClippingRange(3.2, 10.2)
    camera.SetViewUp(0.3, 1.0, 0.13)
    ren.SetActiveCamera(camera)

    renWin.Render()
    renWin.SetWindowName("CallBack")

    axes1 = MakeAxesActor()
    om1 = vtk.vtkOrientationMarkerWidget()
    om1.SetOrientationMarker(axes1)
    # Position lower left in the viewport.
    om1.SetViewport(0, 0, 0.2, 0.2)
    om1.SetInteractor(iren)
    om1.EnabledOn()
    om1.InteractiveOn()

    # Set up the callback.
    # We are going to output the camera position when the event is triggered
    #  so we add the active camera as an attribute.
    GetOrientation.cam = ren.GetActiveCamera()

    # Register the callback with the object that is observing.
    iren.AddObserver('EndInteractionEvent', GetOrientation)
    iren.Initialize()
    iren.Start()


def GetOrientation(caller, ev):
    """
     Print out the orientation.
    :param caller:
    :param ev: The event.
    :return:
    """
    # Just do this to demonstrate who called callback and the event that triggered it.
    print(caller.GetClassName(), "Event Id:", ev)

    # We must do this before we register the callback in the calling function.
    # GetOrientation.cam = ren.GetActiveCamera()

    # Now print the camera orientation.
    fmt1 = "{:>15s}"
    fmt2 = "{:9.6g}"
    print(fmt1.format("Position:"), ', '.join(map(fmt2.format, GetOrientation.cam.GetPosition())))
    print(fmt1.format("Focal point:"), ', '.join(map(fmt2.format, GetOrientation.cam.GetFocalPoint())))
    print(fmt1.format("Clipping range:"), ', '.join(map(fmt2.format, GetOrientation.cam.GetClippingRange())))
    print(fmt1.format("View up:"), ', '.join(map(fmt2.format, GetOrientation.cam.GetViewUp())))
    print(fmt1.format("Distance:"), fmt2.format(GetOrientation.cam.GetDistance()))


def MakeAxesActor():
    axes = vtk.vtkAxesActor()
    axes.SetShaftTypeToCylinder()
    axes.SetXAxisLabelText('X')
    axes.SetYAxisLabelText('Y')
    axes.SetZAxisLabelText('Z')
    axes.SetTotalLength(1.0, 1.0, 1.0)
    axes.SetCylinderRadius(0.5 * axes.GetCylinderRadius())
    axes.SetConeRadius(1.025 * axes.GetConeRadius())
    axes.SetSphereRadius(1.5 * axes.GetSphereRadius())
    return axes


if __name__ == '__main__':
    main()