Correctly SetInputData of ExtractSelection

Support
1

Hello, I need a little help to understand how to use the SetInputData method of a vtkExtractSelektion class instance.I am looking specifically at this example here: https://examples.vtk.org/site/Python/Picking/CellPicking/ . The newly created Interactor can pick the displayed face (“Cell”). It works fine, as long as I only have one object there.
In my code I need a box that is formed of 6 sides. I build each of the sides out if a vtkQuad object and stored the related polydata of each quad in a list = [quad0, quad1, … ]. If I adjust the code, I can use the

extract_selection.SetInputData(0, self.data)

Function and pass one of these quads (because its a vtkDataObject). It works fine, I can pick it. What does not work, is passing multiple of these polydata objects. Or at least, I have not figured out how. If I add them at higher integers (e.g. SetInputData(0, quad1), SetInputData(1, quad2)) I receive an error message that there are 6 or 7 input connections but it is not repeatable or something.

So it boils down to this: how can I provide the extract_selection with more than one polydata object, so that I can pick either of the six sides I defined? I am happy with any leads about important concepts I am probably missing to figure this out by myself. Thank you.

2

I did a little more research:
As per the documentation, extract_selection accepts only 2 InputData slots, 0 → the data and 1 → the selection. So my second approach above is expected to fail.

The following working example is a merge of the linked CellPicking and vtkQuad examples and basically shows what I want to do - with 1 quad. As described above, I need it working with 6 selectable quads.
I tried grouping the quads polydata in a vtkMultiBlockDataSet, and provide this as the InputData at index 0, but then nothing is selected, no matter where I click in the viewport.

from vtkmodules.vtkCommonColor import vtkNamedColors
from vtkmodules.vtkCommonCore import vtkIdTypeArray
from vtkmodules.vtkCommonDataModel import (
    vtkSelection,
    vtkSelectionNode,
    vtkUnstructuredGrid
)
from vtkmodules.vtkFiltersExtraction import vtkExtractSelection
from vtkmodules.vtkRenderingCore import (
    vtkActor,
    vtkCellPicker,
    vtkDataSetMapper,
    vtkPolyDataMapper,
    vtkRenderWindow,
    vtkRenderWindowInteractor,
    vtkRenderer
)

from vtk import *


# Catch mouse events
class MouseInteractorStyle(vtkInteractorStyleTrackballCamera):
    def __init__(self, data):
        self.AddObserver('LeftButtonPressEvent', self.left_button_press_event)
        self.data = data
        self.selected_mapper = vtkDataSetMapper()
        self.selected_actor = vtkActor()

    def left_button_press_event(self, obj, event):
        colors = vtkNamedColors()

        # Get the location of the click (in window coordinates)
        pos = self.GetInteractor().GetEventPosition()

        picker = vtkCellPicker()
        picker.SetTolerance(0.0005)

        # Pick from this location.
        picker.Pick(pos[0], pos[1], 0, self.GetDefaultRenderer())

        world_position = picker.GetPickPosition()
        print(f'Cell id is: {picker.GetCellId()}')

        if picker.GetCellId() != -1:
            print(f'Pick position is: ({world_position[0]:.6g}, {world_position[1]:.6g}, {world_position[2]:.6g})')

            ids = vtkIdTypeArray()
            ids.SetNumberOfComponents(1)
            ids.InsertNextValue(picker.GetCellId())

            selection_node = vtkSelectionNode()
            selection_node.SetFieldType(vtkSelectionNode.CELL)
            selection_node.SetContentType(vtkSelectionNode.INDICES)
            selection_node.SetSelectionList(ids)

            selection = vtkSelection()
            selection.AddNode(selection_node)

            extract_selection = vtkExtractSelection()
            extract_selection.SetInputData(0, self.data)
            extract_selection.SetInputData(1, selection)
            extract_selection.Update()

            # In selection
            selected = vtkUnstructuredGrid()
            selected.ShallowCopy(extract_selection.GetOutput())

            print(f'Number of points in the selection: {selected.GetNumberOfPoints()}')
            print(f'Number of cells in the selection : {selected.GetNumberOfCells()}')

            self.selected_mapper.SetInputData(selected)
            self.selected_actor.SetMapper(self.selected_mapper)
            self.selected_actor.GetProperty().EdgeVisibilityOn()
            self.selected_actor.GetProperty().SetColor(colors.GetColor3d('Tomato'))

            self.selected_actor.GetProperty().SetLineWidth(3)

            self.GetInteractor().GetRenderWindow().GetRenderers().GetFirstRenderer().AddActor(self.selected_actor)
            self.selected_actor.VisibilityOn()

        else:
            if hasattr(self, 'selected_actor'):
                self.selected_actor.VisibilityOff()

        # Forward events
        self.OnLeftButtonDown()


def main(argv):
    colors = vtkNamedColors()

    # Annotate the points
    # https: // examples.vtk.org / site / Cxx / Annotation / TextOrigin /
    # Create four points (must be in counter clockwise order)
    p0 = [0.0, 0.0, 0.0]
    p1 = [1.0, 0.0, 0.0]
    p2 = [1.0, 1.0, 0.0]
    p3 = [0.0, 1.0, 0.0]

    # Add the points to a vtkPoints object
    points = vtkPoints()
    points.InsertNextPoint(p0)
    points.InsertNextPoint(p1)
    points.InsertNextPoint(p2)
    points.InsertNextPoint(p3)

    # Create a quad on the four points
    quad = vtkQuad()
    quad.GetPointIds().SetId(0, 0)
    quad.GetPointIds().SetId(1, 1)
    quad.GetPointIds().SetId(2, 2)
    quad.GetPointIds().SetId(3, 3)

    # Create a cell array to store the quad in
    quads = vtkCellArray()
    quads.InsertNextCell(quad)

    # Create a polydata to store everything in
    polydata = vtkPolyData()

    # Add the points and quads to the dataset
    polydata.SetPoints(points)
    polydata.SetPolys(quads)

    mapper = vtkPolyDataMapper()
    mapper.SetInputData(polydata)

    actor = vtkActor()
    actor.GetProperty().SetColor(colors.GetColor3d('SeaGreen'))
    actor.GetProperty().SetOpacity(0.1)
    actor.SetMapper(mapper)

    renderer = vtkRenderer()
    ren_win = vtkRenderWindow()
    ren_win.AddRenderer(renderer)
    ren_win.SetWindowName('CellPicking')
    iren = vtkRenderWindowInteractor()
    iren.SetRenderWindow(ren_win)

    renderer.AddActor(actor)
    # renderer.ResetCamera()
    renderer.SetBackground(colors.GetColor3d('White'))

    # Add the custom style.
    style = MouseInteractorStyle(polydata)
    style.SetDefaultRenderer(renderer)
    iren.SetInteractorStyle(style)

    ren_win.Render()
    iren.Initialize()
    iren.Start()


if __name__ == '__main__':
    import sys

    main(sys.argv)