# QuadraticHexahedronDemo

VTKExamples/Python/GeometricObjects/QuadraticHexahedronDemo

### Description

This example shows the effect of changing the chord length error for a vtkQuadraticHexahedron.

Other Languages

See (Cxx)

### Code

QuadraticHexahedronDemo.py

    #!/usr/bin/env python
    # -*- coding: utf-8 -*-

    import vtk

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

        uGrid = MakeQuadraticHexahedron()

        tessellate = vtk.vtkTessellatorFilter()
        tessellate.SetInputData(uGrid)
        tessellate.SetChordError(0.035)
        tessellate.Update()

        cellMap = dict()

        numTets = 0
        cell = vtk.vtkGenericCell()
        it = tessellate.GetOutput().NewCellIterator()
        it.InitTraversal()
        while not it.IsDoneWithTraversal():
            it.GetCell(cell)
            cellMap[cell.GetRepresentativeCell().GetClassName()] = numTets
            numTets += 1
            it.GoToNextCell()

        mapper = vtk.vtkDataSetMapper()
        mapper.SetInputConnection(tessellate.GetOutputPort())
        mapper.ScalarVisibilityOff()

        # Create an actor for the grid
        actor = vtk.vtkActor()
        actor.SetMapper(mapper)
        actor.GetProperty().SetDiffuseColor(
            namedColors.GetColor3d("Tomato"))
        actor.GetProperty().SetEdgeColor(
            namedColors.GetColor3d("IvoryBlack"))
        actor.GetProperty().EdgeVisibilityOn()

        sphereSource = vtk.vtkSphereSource()
        sphereSource.SetRadius(0.02)

        glyph3D = vtk.vtkGlyph3D()
        glyph3D.SetInputData(uGrid)
        glyph3D.SetSourceConnection(sphereSource.GetOutputPort())
        glyph3D.ScalingOff()
        glyph3D.Update()

        glyph3DMapper = vtk.vtkDataSetMapper()
        glyph3DMapper.SetInputConnection(glyph3D.GetOutputPort())
        glyph3DMapper.ScalarVisibilityOff()

        glyph3DActor = vtk.vtkActor()
        glyph3DActor.SetMapper(glyph3DMapper)
        glyph3DActor.GetProperty().SetColor(
            namedColors.GetColor3d("Banana"))

        textProperty = vtk.vtkTextProperty()
        textProperty.SetFontSize(24)

        ss = "# of Tetras: " + str(numTets)
        textMapper = vtk.vtkTextMapper()
        textMapper.SetInput(ss)
        textMapper.SetTextProperty(textProperty)

        textActor = vtk.vtkActor2D()
        textActor.SetMapper(textMapper)
        textActor.SetPosition(10, 400)

        # Visualize
        renderer = vtk.vtkRenderer()
        renderWindow = vtk.vtkRenderWindow()
        renderWindow.SetWindowName("Quadratic Hexahedron Demo")
        renderWindow.AddRenderer(renderer)
        renderWindow.SetSize(640, 512)
        interactor = vtk.vtkRenderWindowInteractor()
        interactor.SetRenderWindow(renderWindow)

        widget = vtk.vtkSliderWidget()
        MakeWidget(widget, tessellate, textMapper, interactor)

        renderer.AddActor(actor)
        renderer.AddActor(glyph3DActor)
        renderer.AddViewProp(textActor)
        renderer.SetBackground(namedColors.GetColor3d("SlateGray"))

        renderWindow.Render()

        interactor.Start()

    class SliderCallbackChordError():
        def __init__(self, tessellate, textMapper):
            self.tessellate = tessellate
            self.textMapper = textMapper

        def __call__(self, caller, ev):
            sliderWidget = caller
            value = sliderWidget.GetRepresentation().GetValue()
            self.tessellate.SetChordError(value)
            self.tessellate.SetMaximumNumberOfSubdivisions(4)
            self.tessellate.Update()

            cellMap = dict()

            numTets = 0
            cell = vtk.vtkGenericCell()
            it = self.tessellate.GetOutput().NewCellIterator()
            it.InitTraversal()
            while not it.IsDoneWithTraversal():
                it.GetCell(cell)
                cellMap[cell.GetRepresentativeCell().GetClassName()] = numTets
                numTets += 1
                it.GoToNextCell()
            ss = "# of Tetras: " + str(numTets)
            self.textMapper.SetInput(ss)

    def MakeWidget(widget, tessellate, textMapper, interactor):
        # Setup a slider widget for each varying parameter
        tubeWidth = 0.008
        sliderLength = 0.008
        titleHeight = 0.04
        labelHeight = 0.04

        sliderRepChordError = vtk.vtkSliderRepresentation2D()

        sliderRepChordError.SetMinimumValue(0.0)
        sliderRepChordError.SetMaximumValue(0.07)
        sliderRepChordError.SetValue(tessellate.GetChordError())
        sliderRepChordError.SetTitleText("Chord error")

        sliderRepChordError.GetPoint1Coordinate().SetCoordinateSystemToNormalizedDisplay()
        sliderRepChordError.GetPoint1Coordinate().SetValue(0.1, 0.1)
        sliderRepChordError.GetPoint2Coordinate().SetCoordinateSystemToNormalizedDisplay()
        sliderRepChordError.GetPoint2Coordinate().SetValue(0.9, 0.1)

        sliderRepChordError.SetTubeWidth(tubeWidth)
        sliderRepChordError.SetSliderLength(sliderLength)
        sliderRepChordError.SetTitleHeight(titleHeight)
        sliderRepChordError.SetLabelHeight(labelHeight)

        widget.SetInteractor(interactor)
        widget.SetRepresentation(sliderRepChordError)
        widget.SetAnimationModeToAnimate()
        widget.EnabledOn()

        widget.AddObserver(vtk.vtkCommand.InteractionEvent, SliderCallbackChordError(tessellate, textMapper))

    def MakeQuadraticHexahedron():
        aHexahedron = vtk.vtkQuadraticHexahedron()
        points = vtk.vtkPoints()

        pcoords = aHexahedron.GetParametricCoords()
        rng = vtk.vtkMinimalStandardRandomSequence()
        points.SetNumberOfPoints(aHexahedron.GetNumberOfPoints())
        rng.SetSeed(5070)  # for testing
        for i in range(0, aHexahedron.GetNumberOfPoints()):
            perturbation = [0.0] * 3
            for j in range(0, 3):
                rng.Next()
                perturbation[j] = rng.GetRangeValue(-0.1, 0.1)
            aHexahedron.GetPointIds().SetId(i, i)
            points.SetPoint(i, pcoords[3 * i] + perturbation[0],
                            pcoords[3 * i + 1] + perturbation[1],
                            pcoords[3 * i + 2] + perturbation[2])

        # Add the points and hexahedron to an unstructured grid
        uGrid = vtk.vtkUnstructuredGrid()
        uGrid.SetPoints(points)
        uGrid.InsertNextCell(aHexahedron.GetCellType(), aHexahedron.GetPointIds())

        return uGrid

    if __name__ == '__main__':
        main()