Use Scalar And vtkColorTransferFunction To Set Different Color For Polydata

How to set different colors for different parts of a single 3D model? The article introduces a way that set scalars for pointData and map the information by vtkColorTransferFunction object, then vtkPolyDataMapper object configure a correct scalar mode and use vtkColorTransferFunction object as its lookupTable.

The code snippet shows all details of implementation, the data file curve.vtp can be downloaded from my github repository documents

#define vtkSPtr vtkSmartPointer
#define vtkSPtrNew(Var, Type) vtkSPtr<Type> Var = vtkSPtr<Type>::New();

using namespace std;

int main()
{
    vtkSPtrNew( reader, vtkXMLPolyDataReader );
    reader->SetFileName( "/Users/weiyang/Desktop/curve.vtp" );
    reader->Update();

    vtkPolyData *pd = reader->GetOutput();
    vtkPoints *points = pd->GetPoints();
    int ptsCount = pd->GetNumberOfPoints();

    vtkSPtrNew( scalars, vtkCharArray );
    scalars->SetNumberOfTuples( ptsCount );
    enum E_Colors{ RED, GREEN, BLUE };
    E_Colors COLORS[3] = { RED, GREEN, BLUE };
    for( int i = 0; i < ptsCount / 4; ++i )
    {
        scalars->SetTuple1(i, RED);
    }
    for( int i = ptsCount / 4; i < ptsCount / 2; ++i )
    {
        scalars->SetTuple1(i, GREEN);
    }
    for( int i = ptsCount / 2; i < ptsCount; ++i )
    {
        scalars->SetTuple1(i, BLUE);
    }

    pd->GetPointData()->SetScalars( scalars );

    vtkSPtrNew( mapper, vtkPolyDataMapper );
    mapper->SetInputConnection( reader->GetOutputPort() );
    mapper->SetScalarModeToUsePointData();

    vtkSPtrNew( lut, vtkColorTransferFunction );
    lut->SetClamping( 0 );
    int colorParameters[3][3] = { {255, 0, 0}, {0, 255, 0}, {0, 0, 255} };
    for( int i = 0; i < 3; ++i )
    {
        lut->AddRGBPoint( COLORS[i], colorParameters[i][0]/255.0, colorParameters[i][1]/255.0, colorParameters[i][2]/255.0 );
    }
    mapper->SetLookupTable( lut );
    mapper->SetScalarRange( COLORS[0], COLORS[2] );

    vtkSPtrNew( actor, vtkActor );
    actor->SetMapper( mapper );
    actor->GetProperty()->SetLineWidth( 3 );
    vtkSPtrNew( axesActor, vtkAxesActor );

    vtkSPtrNew( renderer, vtkRenderer );
    renderer->AddActor( actor );
    renderer->AddActor( axesActor );
    renderer->SetBackground( 0, 0, 0 );

    vtkSPtrNew( renderWindow, vtkRenderWindow );
    renderWindow->AddRenderer( renderer );

    vtkSPtrNew( renderWindowInteractor, vtkRenderWindowInteractor );
    renderWindowInteractor->SetRenderWindow( renderWindow );

    renderer->ResetCamera();
    renderWindow->Render();
    renderWindowInteractor->Start();
    return 0;
}

Header files:

#include <iostream>
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>
#include <vtkActor.h>
#include <vtkConeSource.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkPolyDataMapper.h>
#include <vtkLineSource.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkAxesActor.h>
#include <vtkProperty.h>
#include <vtkXMLPolyDataReader.h>
#include <vtkCharArray.h>
#include <vtkPointData.h>
#include <vtkColorTransferFunction.h>