# WalkCow

VTKExamples/Python/Rendering/WalkCow

### Description

This generates Fig 3-31: Rotations of a cow about her axes.; Fig. 3-32: The cow "walking" around the global origin; Fig. 3-33: The cow rotating about a vector passing through her nose found in VTKTextbook.pdf.

### Code

WalkCow.py

    #!/usr/local/bin/python

    #  Translated from walkCow.tcl

    import vtk

    def main():
        file_name, figure = get_program_parameters()
        figure = abs(figure)
        if figure > 2:
            figure = 0

        colors = vtk.vtkNamedColors()
        # Set the background color. Match those in VTKTextbook.pdf.
        bkg1 = map(lambda x: x / 256.0, [60, 93, 144])
        bkg2 = map(lambda x: x / 256.0, [25, 51, 102])
        colors.SetColor("BkgColor1", *bkg1)
        colors.SetColor("BkgColor2", *bkg2)

        ren = vtk.vtkRenderer()
        renWin = vtk.vtkRenderWindow()
        renWin.AddRenderer(ren)

        iren = vtk.vtkRenderWindowInteractor()
        iren.SetRenderWindow(renWin)

        # The cow pipeline.
        cow = vtk.vtkBYUReader()
        cow.SetGeometryFileName(file_name)
        cow.Update()

        cowMapper = vtk.vtkPolyDataMapper()
        cowMapper.SetInputConnection(cow.GetOutputPort())
        cowMapper.ScalarVisibilityOff()

        cowActor = vtk.vtkActor()
        cowActor.SetMapper(cowMapper)
        cowActor.GetProperty().SetColor(colors.GetColor3d("Wheat"))

        ren.AddActor(cowActor)

        # Axes pipeline.
        cowAxesSource = vtk.vtkAxes()
        cowAxesSource.SetScaleFactor(10.0)
        cowAxesSource.SetOrigin(0, 0, 0)

        cowAxesMapper = vtk.vtkPolyDataMapper()
        cowAxesMapper.SetInputConnection(cowAxesSource.GetOutputPort())

        cowAxes = vtk.vtkActor()
        cowAxes.SetMapper(cowAxesMapper)
        cowAxes.VisibilityOff()

        ren.AddActor(cowAxes)

        ren.SetBackground(colors.GetColor3d("BkgColor1"))
        renWin.SetSize(600, 480)

        iren.Initialize()
        cowAxes.VisibilityOn()
        renWin.Render()

        # Activate this if you want to see the Position and Focal point.
        # ren.GetActiveCamera().AddObserver('ModifiedEvent', CameraModifiedCallback)

        # These four walks use the same camera position.
        Rotate_X(cowActor, ren, renWin)
        Rotate_Y(cowActor, ren, renWin)
        Rotate_Z(cowActor, ren, renWin)
        Rotate_XY(cowActor, ren, renWin)

        ren.SetBackground(colors.GetColor3d("BkgColor2"))
        if figure == 1:
            Rotate_V_0(cowActor, ren, renWin)
        elif figure == 2:
            Rotate_V_V(cowActor, ren, renWin)
        else:
            Rotate_V_0(cowActor, ren, renWin)
            Rotate_V_V(cowActor, ren, renWin)
            # Walk() needs to go after Rotate_V_0() or Rotate_V_V().
            Walk(cowActor, ren, renWin)

        # Interact with data.
        renWin.EraseOff()
        iren.Start()

    def get_program_parameters():
        import argparse
        description = 'Produce figures: 3-31, 3-32, 3-33 from the VTK Textbook.'
        epilogue = '''
            Produce figures 3-31, 3-32, 3-33 from the VTK Textbook.
            It is a translation of the original WalkCow.tcl with a few additional enhancements.
       '''
        parser = argparse.ArgumentParser(description=description, epilog=epilogue)
        parser.add_argument('filename', help='The file cow.g.')
        parser.add_argument('figure', default=0, type=int, nargs='?', help='The particular rotation that you want to view.')
        args = parser.parse_args()
        return args.filename, args.figure

    """
      These Rotate* and Walk functions create a scene where multiple
         views of the object exist.

        They all operate in a similar manner, namely:
        1) Accept vtkActor, vtkRenderer, vtkRenderWindow as parameters.
        2) Position the object.
        3) Position the observer with the focal point sent to the centre
            of the object.
        4) Render and set EraseOff() in the render window.
           Note that:
            EraseOff() has to be called after a Render() call
             to work in the desired way.
        5) Then rotate or Walk the object around the scene.
        6) Optionally write out the scene using Screenshot().
        6) Set EraseOff() in the render window.
        7) Reset the object position.

    """

    def Rotate_X(cowActor, ren, renWin):
        # Six rotations about the x axis.
        ren.ResetCamera()
        ren.ResetCameraClippingRange()
        cowActor.SetOrientation(0.0, 0.0, 0.0)
        cowActor.SetOrigin(0.0, 0.0, 0)
        cowActor.SetPosition(0, 0, 0)
        # Get the focal point.
        bounds = cowActor.GetBounds()
        fp = [0.0] * 3
        for i in range(0, 3):
            fp[i] = (bounds[i * 2 + 1] + bounds[i * 2]) / 2.0
        # This closely matches the original illustration.
        ren.GetActiveCamera().SetPosition(2, 25, 0)
        ren.GetActiveCamera().SetFocalPoint(fp)
        ren.GetActiveCamera().SetViewUp(0, 0, -1)
        ren.ResetCameraClippingRange()
        renWin.Render()
        renWin.Render()
        renWin.EraseOff()
        for idx in range(0, 6):
            cowActor.RotateX(60)
            renWin.Render()
            renWin.Render()
        # Screenshot("Fig3-31a.png", renWin)
        renWin.EraseOn()

    def Rotate_Y(cowActor, ren, renWin):
        # Six rotations about the y axis.
        ren.ResetCamera()
        ren.ResetCameraClippingRange()
        cowActor.SetOrientation(0.0, 0.0, 0.0)
        cowActor.SetOrigin(0.0, 0.0, 0)
        cowActor.SetPosition(0, 0, 0)
        # Get the focal point.
        bounds = cowActor.GetBounds()
        fp = [0.0] * 3
        for i in range(0, 3):
            fp[i] = (bounds[i * 2 + 1] + bounds[i * 2]) / 2.0
        # This closely matches the original illustration.
        ren.GetActiveCamera().SetPosition(2, 0, 25)
        ren.GetActiveCamera().SetFocalPoint(fp)
        ren.GetActiveCamera().SetViewUp(0, 1, 0)
        ren.ResetCameraClippingRange()
        renWin.Render()
        renWin.Render()
        renWin.EraseOff()
        for idx in range(0, 6):
            cowActor.RotateY(60)
            renWin.Render()
            renWin.Render()
        # Screenshot("Fig3-31b.png", renWin)
        renWin.EraseOn()

    def Rotate_Z(cowActor, ren, renWin):
        # Six rotations about the z axis.
        ren.ResetCamera()
        ren.ResetCameraClippingRange()
        cowActor.SetOrientation(0.0, 0.0, 0.0)
        cowActor.SetOrigin(0.0, 0.0, 0)
        cowActor.SetPosition(0, 0, 0)
        # Get the focal point.
        bounds = cowActor.GetBounds()
        fp = [0.0] * 3
        for i in range(0, 3):
            fp[i] = (bounds[i * 2 + 1] + bounds[i * 2]) / 2.0
        # This closely matches the original illustration.
        # ren.GetActiveCamera().SetPosition(2, 0, 25)
        ren.GetActiveCamera().SetPosition(2, 0, 25)
        ren.GetActiveCamera().SetFocalPoint(fp)
        ren.GetActiveCamera().SetViewUp(0, 1, 0)
        ren.ResetCameraClippingRange()
        renWin.Render()
        renWin.Render()
        renWin.EraseOff()
        for idx in range(0, 6):
            cowActor.RotateZ(60)
            renWin.Render()
            renWin.Render()
        # Screenshot("Fig3-31c.png", renWin)
        renWin.EraseOn()

    def Rotate_XY(cowActor, ren, renWin):
        # First a rotation about the x axis, then six rotations about the y axis.
        ren.ResetCamera()
        ren.ResetCameraClippingRange()
        cowActor.SetOrientation(0.0, 0.0, 0.0)
        cowActor.SetOrigin(0.0, 0.0, 0)
        cowActor.SetPosition(0, 0, 0)
        # Get the focal point.
        bounds = cowActor.GetBounds()
        fp = [0.0] * 3
        for i in range(0, 3):
            fp[i] = (bounds[i * 2 + 1] + bounds[i * 2]) / 2.0
        # This closely matches the original illustration.
        # ren.GetActiveCamera().SetPosition(2, 0, 24)
        ren.GetActiveCamera().SetPosition(2, 0, 25)
        ren.GetActiveCamera().SetFocalPoint(fp)
        ren.GetActiveCamera().SetViewUp(0, 1, 0)
        ren.ResetCameraClippingRange()
        renWin.Render()
        renWin.Render()
        renWin.EraseOff()
        cowActor.RotateX(60)
        for idx in range(0, 6):
            cowActor.RotateY(60)
            renWin.Render()
            renWin.Render()
        cowActor.RotateX(-60)
        # Screenshot("Fig3-31d.png", renWin)
        renWin.EraseOn()

    def Rotate_V_0(cowActor, ren, renWin):
        # The cow rotating about a vector passing through her nose.
        # With the origin at (0, 0, 0).
        ren.ResetCamera()
        ren.ResetCameraClippingRange()
        cowActor.SetOrientation(0.0, 0.0, 0.0)
        cowActor.SetOrigin(0.0, 0.0, 0)
        cowActor.SetPosition(0, 0, 0)
        # Get the focal point.
        bounds = cowActor.GetBounds()
        fp = [0.0] * 3
        for i in range(0, 3):
            fp[i] = (bounds[i * 2 + 1] + bounds[i * 2]) / 2.0
        cowPos = vtk.vtkTransform()
        cowPos.Identity()
        cowPos.SetMatrix(cowActor.GetMatrix())
        cowTransform = vtk.vtkTransform()
        cowTransform.Identity()
        cowActor.SetUserMatrix(cowTransform.GetMatrix())
        # This closely matches the original illustration.
        ren.GetActiveCamera().SetPosition(16, 9, -12)
        ren.GetActiveCamera().SetFocalPoint(fp)
        ren.ResetCameraClippingRange()
        renWin.Render()
        renWin.Render()
        renWin.EraseOff()
        for idx in range(0, 6):
            cowActor.RotateWXYZ(60, 2.19574, -1.42455, -0.0331036)
            renWin.Render()
            renWin.Render()
        # Screenshot("Fig3-33a.png", renWin)
        renWin.EraseOn()
        # Put the cow back on the origin.
        # for idx in range(0, 6):
        #     cowActor.RotateWXYZ(-60, 2.19574, -1.42455, -0.0331036)
        # cowActor.SetUserMatrix(cowPos.GetMatrix())
        # ren.GetActiveCamera().SetPosition(0, 0, 1)
        # ren.GetActiveCamera().SetViewUp(0, 1, 0)
        # ren.ResetCamera()

    def Rotate_V_V(cowActor, ren, renWin):
        # The cow rotating about a vector passing through her nose.
        # With the origin at (6.11414, 1.27386, 0.015175).
        ren.ResetCamera()
        ren.ResetCameraClippingRange()
        cowActor.SetOrientation(0.0, 0.0, 0.0)
        cowActor.SetOrigin(0.0, 0.0, 0)
        cowActor.SetPosition(0, 0, 0)
        # Get the focal point.
        bounds = cowActor.GetBounds()
        fp = [0.0] * 3
        for i in range(0, 3):
            fp[i] = (bounds[i * 2 + 1] + bounds[i * 2]) / 2.0
        cowPos = vtk.vtkTransform()
        cowPos.Identity()
        cowPos.SetMatrix(cowActor.GetMatrix())
        cowActor.SetOrigin(6.11414, 1.27386, 0.015175)  # The cow's nose
        cowTransform = vtk.vtkTransform()
        cowTransform.Identity()
        cowActor.SetUserMatrix(cowTransform.GetMatrix())
        # This closely matches the original illustration.
        ren.GetActiveCamera().SetPosition(31, 23, -21)
        ren.GetActiveCamera().SetFocalPoint(fp)
        ren.ResetCameraClippingRange()
        renWin.Render()
        renWin.Render()
        renWin.EraseOff()
        for idx in range(0, 6):
            cowActor.RotateWXYZ(60, 2.19574, -1.42455, -0.0331036)
            renWin.Render()
            renWin.Render()
        # Screenshot("Fig3-33b.png", renWin)
        renWin.EraseOn()
        # Put the cow back on the origin.
        # for idx in range(0, 6):
        #     cowActor.RotateWXYZ(-60, 2.19574, -1.42455, -0.0331036)
        # cowActor.SetUserMatrix(cowPos.GetMatrix())

    def Walk(cowActor, ren, renWin):
        # The cow "walking" around the global origin
        cowPos = vtk.vtkTransform()
        cowPos.Identity()
        cowPos.SetMatrix(cowActor.GetMatrix())
        cowActor.SetOrientation(0.0, 0.0, 0.0)
        cowActor.SetOrigin(0.0, 0.0, 0.0)
        # Get the focal point.
        bounds = cowActor.GetBounds()
        fp = [0.0] * 3
        for i in range(0, 3):
            fp[i] = (bounds[i * 2 + 1] + bounds[i * 2]) / 2.0
        cowTransform = vtk.vtkTransform()
        cowTransform.Identity()
        cowTransform.Translate(0, 0, 5)
        cowActor.SetUserMatrix(cowTransform.GetMatrix())
        # This closely matches the original illustration.
        ren.GetActiveCamera().SetPosition(1, 24, 16)
        ren.GetActiveCamera().SetFocalPoint(fp)
        ren.GetActiveCamera().SetViewUp(0, 0, -1)
        ren.ResetCameraClippingRange()
        renWin.Render()
        renWin.Render()
        renWin.EraseOff()
        for idx in range(1, 7):
            cowTransform.Identity()
            cowTransform.RotateY(idx * 60)
            cowTransform.Translate(0, 0, 5)
            cowActor.SetUserMatrix(cowTransform.GetMatrix())
            renWin.Render()
            renWin.Render()
        # Screenshot("Fig3-32.png", renWin)
        renWin.EraseOn()
        # Walkies are over, put the cow back on the origin.
        # cowActor.SetUserMatrix(cowPos.GetMatrix())

    def CameraModifiedCallback(caller, ev):
        """
         Used to estimate positions similar to the book illustrations.
        :param caller:
        :return:
        """
        print(caller.GetClassName(), "modified")
        # Print the interesting stuff.
        print("\tPosition: ",
              caller.GetPosition()[0], ", ",
              caller.GetPosition()[1], ", ",
              caller.GetPosition()[2])
        print("\tFocal point: ",
              caller.GetFocalPoint()[0], ", ",
              caller.GetFocalPoint()[1], ", ",
              caller.GetFocalPoint()[2])

    def Screenshot(fileName, renWin):
        """
        Save a screenshot.
        :param fileName:
        :param renWin:
        :return:
        """
        windowToImageFilter = vtk.vtkWindowToImageFilter()
        windowToImageFilter.SetInput(renWin)
        windowToImageFilter.SetScale(1)  # image quality
        # We are not recording the alpha (transparency) channel.
        # windowToImageFilter.SetInputBufferTypeToRGBA()
        windowToImageFilter.SetInputBufferTypeToRGB()
        # Read from the front buffer.
        windowToImageFilter.ReadFrontBufferOff()
        windowToImageFilter.Update()

        writer = vtk.vtkPNGWriter()
        writer.SetFileName(fileName)
        writer.SetInputConnection(windowToImageFilter.GetOutputPort())
        writer.Write()

    if __name__ == '__main__':
        main()