How to change the colors of objects in VTK when using vtkAppendPolyData?

Question

I'm trying to modify the color of each object that I've placed in a vtkAppendPolyData but I get weird colors. I mean the object is not in one color but each face of it has a different color.

I would like to have one color by object. Here is the minimal example:

import vtk
sphereSource = vtk.vtkSphereSource()
sphereSource.SetCenter(5,0,0)
sphereSource.Update()
Colors = vtk.vtkUnsignedCharArray()
Colors.SetNumberOfComponents(3)
Cellarray = sphereSource.GetOutput().GetPolys().GetNumberOfCells()
Colors.SetNumberOfTuples(Cellarray)
for c in range(Cellarray):
    Colors.InsertNextTuple3(255, 0, 0)

sphereSource.GetOutput().GetCellData().SetScalars(Colors)
sphereSource.Update()


coneSource =vtk.vtkConeSource()
coneSource.Update()
Colors = vtk.vtkUnsignedCharArray()
Colors.SetNumberOfComponents(3)
Cellarray = coneSource.GetOutput().GetPolys().GetNumberOfCells()
Colors.SetNumberOfTuples(Cellarray)
for c in range(Cellarray):
    Colors.InsertNextTuple3(0, 255, 0)
coneSource.GetOutput().GetCellData().SetScalars(Colors)
coneSource.Update()

# Append the two meshes
appendFilter = vtk.vtkAppendPolyData()
appendFilter.AddInputData(sphereSource.GetOutput())
appendFilter.AddInputData(coneSource.GetOutput())

appendFilter.Update()

#  Remove any duplicate points.
cleanFilter = vtk.vtkCleanPolyData()
cleanFilter.SetInputConnection(appendFilter.GetOutputPort())
cleanFilter.Update()

# Create a mapper and actor
mapper = vtk.vtkPolyDataMapper()
# mapper.ScalarVisibilityOn()
mapper.SetInputConnection(cleanFilter.GetOutputPort())
mapper.SetColorModeToDirectScalars()

actor = vtk.vtkActor()
actor.SetMapper(mapper)

# Create a renderer, render window, and interactor
renderer = vtk.vtkRenderer()
renderWindow = vtk.vtkRenderWindow()
renderWindow.AddRenderer(renderer)
renderWindowInteractor = vtk.vtkRenderWindowInteractor()
renderWindowInteractor.SetRenderWindow(renderWindow)

# Add the actors to the scene
renderer.AddActor(actor)
renderer.SetBackground(.3, .2, .1) #  Background color dark red

# Render and interact
renderWindow.Render()
renderWindowInteractor.Start()

Nico Vuaille Nico Vuaille · Accepted Answer · 2020-01-16T10:23:39

As you set the number of tuples, you should use InsertTuple3 and not InsertNextTuple3, as follow:

Colors.SetNumberOfTuples(Cellarray)
for c in range(Cellarray):
    Colors.InsertTuple3(c, 255, 0, 0)

Note that Insert is a confusing name here as it does not change the global size and will overwrite the given index. Is more like a Set method.

How to change the colors of objects in VTK when using vtkAppendPolyData?

1 Answers