VTK/Examples/Python/Visualization/AssignColorsCellFromLUT

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Description

Demonstrates how to assign colors to cells in a vtkPolyData structure using lookup tables. Two techniques are demonstrated:

  1. Using a lookup table of predefined colors.
  2. Using a lookup table generated from a color transfer function.

The resultant display shows in the left-hand column, the cells in a plane colored by the two lookup tables and in the right-hand column, the same polydata that has been read in from a file demonstrating that the structures are identical.

The top row of the display uses the color transfer function to create a green to tan transition in a diverging color space. Note that the central square is white indicating the midpoint.

The bottom row of the display uses a lookup table of predefined colors.

AssignCellColorsFromLUT.py

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

'''
Demonstrates how to assign colors to cells in a vtkPolyData structure using
 lookup tables.
Two techniques are demonstrated:
1) Using a lookup table of predefined colors.
2) Using a lookup table generated from a color transfer function.

The resultant display shows in the left-hand column, the cells in a plane
colored by the two lookup tables and in the right-hand column, the same
polydata that has been read in from a file demonstrating that the structures
are identical.

The top row of the display uses the color transfer function to create a
 green to tan transition in a diverging color space.
 Note that the central square is white indicating the midpoint.
The bottom row of the display uses a lookup table of predefined colors.
'''

from __future__ import print_function
import vtk

def MakeLUT(tableSize):
    '''
    Make a lookup table from a set of named colors.
    :param: tableSize - The table size
    :return: The lookup table.
    '''
    nc = vtk.vtkNamedColors()

    lut = vtk.vtkLookupTable()
    lut.SetNumberOfTableValues(tableSize)
    lut.Build()

    # Fill in a few known colors, the rest will be generated if needed
    lut.SetTableValue(0,nc.GetColor4d("Black"))
    lut.SetTableValue(1,nc.GetColor4d("Banana"))
    lut.SetTableValue(2,nc.GetColor4d("Tomato"))
    lut.SetTableValue(3,nc.GetColor4d("Wheat"))
    lut.SetTableValue(4,nc.GetColor4d("Lavender"))
    lut.SetTableValue(5,nc.GetColor4d("Flesh"))
    lut.SetTableValue(6,nc.GetColor4d("Raspberry"))
    lut.SetTableValue(7,nc.GetColor4d("Salmon"))
    lut.SetTableValue(8,nc.GetColor4d("Mint"))
    lut.SetTableValue(9,nc.GetColor4d("Peacock"))

    return lut

def MakeLUTFromCTF(tableSize):
    '''
    Use a color transfer Function to generate the colors in the lookup table.
    See: http://www.vtk.org/doc/nightly/html/classvtkColorTransferFunction.html
    :param: tableSize - The table size
    :return: The lookup table.
    '''
    ctf = vtk.vtkColorTransferFunction()
    ctf.SetColorSpaceToDiverging()
    # Green to tan.
    ctf.AddRGBPoint(0.0, 0.085, 0.532, 0.201)
    ctf.AddRGBPoint(0.5, 0.865, 0.865, 0.865)
    ctf.AddRGBPoint(1.0, 0.677, 0.492, 0.093)

    lut = vtk.vtkLookupTable()
    lut.SetNumberOfTableValues(tableSize)
    lut.Build()

    for i in range(0,tableSize):
        rgb = list(ctf.GetColor(float(i)/tableSize))+[1]
        lut.SetTableValue(i,rgb)

    return lut

def MakeCellData(tableSize, lut, colors):
    '''
    Create the cell data using the colors from the lookup table.
    :param: tableSize - The table size
    :param: lut - The lookup table.
    :param: colors - A reference to a vtkUnsignedCharArray().
    '''
    for i in range(1,tableSize):
        rgb = [0.0, 0.0, 0.0]
        lut.GetColor(float(i) / (tableSize - 1),rgb)
        ucrgb = list(map(int, [x * 255 for x in rgb]))
        colors.InsertNextTuple3(ucrgb[0], ucrgb[1], ucrgb[2])
        s = '['+ ', '.join(['{:0.6f}'.format(x) for x in rgb]) + ']'
        print(s, ucrgb)


def main():
    '''
    :return: The render window interactor.
    '''

    nc = vtk.vtkNamedColors()

    # Provide some geometry
    resolution = 3

    plane11 = vtk.vtkPlaneSource()
    plane11.SetXResolution(resolution)
    plane11.SetYResolution(resolution)

    plane12 = vtk.vtkPlaneSource()
    plane12.SetXResolution(resolution)
    plane12.SetYResolution(resolution)

    tableSize = max(resolution * resolution + 1, 10)

    #  Force an update so we can set cell data
    plane11.Update()
    plane12.Update()

    #  Get the lookup tables mapping cell data to colors
    lut1 = MakeLUT(tableSize)
    lut2 = MakeLUTFromCTF(tableSize)

    colorData1 = vtk.vtkUnsignedCharArray()
    colorData1.SetName('colors') # Any name will work here.
    colorData1.SetNumberOfComponents(3)
    print('Using a lookup table from a set of named colors.')
    MakeCellData(tableSize, lut1, colorData1)
    # Then use SetScalars() to add it to the vtkPolyData structure,
    # this will then be interpreted as a color table.
    plane11.GetOutput().GetCellData().SetScalars(colorData1)

    colorData2 = vtk.vtkUnsignedCharArray()
    colorData2.SetName('colors') # Any name will work here.
    colorData2.SetNumberOfComponents(3)
    print('Using a lookup table created from a color transfer function.')
    MakeCellData(tableSize, lut2, colorData2)
    plane12.GetOutput().GetCellData().SetScalars(colorData2)

    # Set up actor and mapper
    mapper11 = vtk.vtkPolyDataMapper()
    mapper11.SetInputConnection(plane11.GetOutputPort())
    # Now, instead of doing this:
    # mapper11.SetScalarRange(0, tableSize - 1)
    # mapper11.SetLookupTable(lut1)
    # We can just use the color data that we created from the lookup table and
    # assigned to the cells:
    mapper11.SetScalarModeToUseCellData()
    mapper11.Update()

    mapper12 = vtk.vtkPolyDataMapper()
    mapper12.SetInputConnection(plane12.GetOutputPort())
    mapper12.SetScalarModeToUseCellData()
    mapper12.Update()

    writer = vtk.vtkXMLPolyDataWriter()
    writer.SetFileName('pdlut.vtp')
    writer.SetInputData(mapper11.GetInput())
    # This is set so we can see the data in a text editor.
    writer.SetDataModeToAscii()
    writer.Write()
    writer.SetFileName('pdctf.vtp')
    writer.SetInputData(mapper12.GetInput())
    writer.Write()

    actor11 = vtk.vtkActor()
    actor11.SetMapper(mapper11)
    actor12 = vtk.vtkActor()
    actor12.SetMapper(mapper12)

    # Let's read in the data we wrote out.
    reader1 = vtk.vtkXMLPolyDataReader()
    reader1.SetFileName("pdlut.vtp")

    reader2 = vtk.vtkXMLPolyDataReader()
    reader2.SetFileName("pdctf.vtp")

    mapper21 = vtk.vtkPolyDataMapper()
    mapper21.SetInputConnection(reader1.GetOutputPort())
    mapper21.SetScalarModeToUseCellData()
    mapper21.Update()
    actor21 = vtk.vtkActor()
    actor21.SetMapper(mapper11)

    mapper22 = vtk.vtkPolyDataMapper()
    mapper22.SetInputConnection(reader2.GetOutputPort())
    mapper22.SetScalarModeToUseCellData()
    mapper22.Update()
    actor22 = vtk.vtkActor()
    actor22.SetMapper(mapper22)

    # Define viewport ranges.
    # (xmin, ymin, xmax, ymax)
    viewport11 = [0.0, 0.0, 0.5, 0.5]
    viewport12 = [0.0, 0.5, 0.5, 1.0]
    viewport21 = [0.5, 0.0, 1.0, 0.5]
    viewport22 = [0.5, 0.5, 1.0, 1.0]

    # Set up the renderers.
    ren11 = vtk.vtkRenderer()
    ren12 = vtk.vtkRenderer()
    ren21 = vtk.vtkRenderer()
    ren22 = vtk.vtkRenderer()

    # Setup the render windows
    renWin = vtk.vtkRenderWindow()
    renWin.SetSize(800, 800)
    renWin.AddRenderer(ren11)
    renWin.AddRenderer(ren12)
    renWin.AddRenderer(ren21)
    renWin.AddRenderer(ren22)
    ren11.SetViewport(viewport11)
    ren12.SetViewport(viewport12)
    ren21.SetViewport(viewport21)
    ren22.SetViewport(viewport22)
    ren11.SetBackground(nc.GetColor3d('MidnightBlue'))
    ren12.SetBackground(nc.GetColor3d('MidnightBlue'))
    ren21.SetBackground(nc.GetColor3d('MidnightBlue'))
    ren22.SetBackground(nc.GetColor3d('MidnightBlue'))
    ren11.AddActor(actor11)
    ren12.AddActor(actor12)
    ren21.AddActor(actor21)
    ren22.AddActor(actor22)

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

    return iren

def CheckVTKVersion(requiredMajorVersion):
    '''
    Check the VTK version.
    :param: requiredMajorVersion e.g. 6
    '''
    version = vtk.vtkVersion()
    if version.GetVTKMajorVersion() > requiredMajorVersion:
        raise
    else:
        return

if __name__ == '__main__':
    try:
        CheckVTKVersion(6)
    except:
        print("You need VTK Version 6 or greater.")
        print("The class vtkNamedColors is in VTK version 6 or greater.")
        exit(0)
    iren = main()
    iren.Start()