[vtkusers] Questions on vtkLookupTable, SetIndexedLookup in connection with graph display

[Frese Daniel Dr.]

Hello list,

I try to display a graph with vertices in three different colors, as defined by a LookupTable. Reading the vtk 6.0 specs I thought that the SetIndexedLookup method would be the right thing to use, but somehow I can't get it working. Most probably I don't understand something very fundamental regarding this graph stuff - it would be great if somebody could shine some light on this.

I put together a small piece of self containing, compilable code, to illustrate my questions. Not, that you might have to replace vtkWin32OpenGLRenderWindow by some class appropriate to your system (I work with Visual Studio 2008 on Windows 7, 64 bit; using a git snapshot a few days old). Here we go with the code :

#include <iostream>

#include "vtkWin32OpenGLRenderWindow.h"
#include "vtkRenderWindow.h"
#include "vtkWin32RenderWindowInteractor.h"
#include "vtkGraphLayoutView.h"
#include "vtkViewTheme.h"
#include "vtkLookupTable.h"
#include "vtkMutableDirectedGraph.h"
#include "vtkTree.h"
#include "vtkIntArray.h"
#include "vtkStringArray.h"
#include "vtkDataRepresentation.h"
#include "vtkRenderedGraphRepresentation.h"
#include "vtkDataSetAttributes.h"

void main() {
      vtkGraphLayoutView* view = vtkGraphLayoutView::New();
      vtkWin32OpenGLRenderWindow* RenderWindow = vtkWin32OpenGLRenderWindow::SafeDownCast(view->GetRenderWindow());

      // Construction of the lookup table, and debug output of GetColor
      vtkLookupTable* lookupTable = vtkLookupTable::New();
      lookupTable->SetNumberOfTableValues(3);
      lookupTable->SetTableValue(0, 1.0, 0.0, 0.0); // red
      lookupTable->SetTableValue(1, 0.0, 0.0, 1.0); // blue
      lookupTable->SetTableValue(2, 1.0, 1.0, 1.0); // white
      lookupTable->SetIndexedLookup(1);
      lookupTable->SetTableRange(0,2);  // this is ignored, if IndexedLookup = true
      lookupTable->Build();

      double rgb[4];
      for (int i=0; i<3; i++) {
            lookupTable->GetColor(i,rgb);
            cout << "Color " << i << " : " << rgb[0] << " " << rgb[1] << " " << rgb[2] << endl;
      }

      // construct view, theme and simple graph to display vertex colors
      vtkViewTheme *theme = vtkViewTheme::New();
      theme->SetPointLookupTable(lookupTable);
      view->ApplyViewTheme(theme);
      vtkMutableDirectedGraph *vtkg = vtkMutableDirectedGraph::New();

      // array to encode the vertex colors
      vtkIntArray *vertexColors = vtkIntArray::New();
      vertexColors->SetNumberOfComponents(1);
      vertexColors->SetName("Vertex Color");
      vertexColors->InsertNextValue(0);
      vertexColors->InsertNextValue(1);
      vertexColors->InsertNextValue(2);

      // array to encode vertex names
      vtkStringArray *names = vtkStringArray::New();
      names->SetName("Vertex Name");
      names->InsertNextValue("0");
      names->InsertNextValue("1");
      names->InsertNextValue("2");

      // construct graph and add color/name arrays
      vtkIdType vtkvertex;
      cout << "vertex 0 : " << (int) (vtkvertex = vtkg->AddVertex()) << endl;
      cout << "vertex 1 : " << (int) vtkg->AddChild(vtkvertex) << endl;
      cout << "vertex 2 : " << (int) vtkg->AddChild(vtkvertex) << endl;

      vtkg->GetVertexData()->AddArray(vertexColors);
      view->SetVertexColorArrayName("Vertex Color");
      vtkg->GetVertexData()->AddArray(names);
      view->SetVertexLabelArrayName("Vertex Name");
      view->SetVertexLabelVisibility(true);

      vtkTree*  vtktree = vtkTree::New();
      vtktree->CheckedShallowCopy(vtkg);
      vtkDataRepresentation* rep = view->SetRepresentationFromInput(vtktree);
      vtkRenderedGraphRepresentation::SafeDownCast(view->GetRepresentation())->ColorVerticesByArrayOn();

      view->Render();
      view->ResetCamera();
      view->GetInteractor()->Initialize();
      view->GetInteractor()->Start();
}

The output in a DOS window is :
Color 0 : 0.501961 0 0
Color 1 : 0.501961 0 0
Color 2 : 0.501961 0 0
vertex 0 : 0
vertex 1 : 1
vertex 2 : 2

The output in a graphical window shows three connected vertices with the following coloring (see attached png) :
Vertex 0  (middle vertex) : blue
Vertex 1 (right vertex) : green
Vertex 2 (left vertex): red

This output is different from the one I expect. Here are my questions:

1)      Why does the output of lookupTable->GetColor() return these strange values ? I would expect, that it returns e.g. for Color 0 the values 1 0 0 (=red). By the way, it behaves as I expect, when I comment the line lookupTable->SetIndexedLookup(1) ...

2)      Why does the graphical output shows vertices in the mentioned colors ? I did not define green at all; I would rather expect the following color scheme:

Vertex 0  (middle vertex) : red

Vertex 1 (right vertex) : blue

Vertex 2 (left vertex): white
                The "wrong" coloring in the output window occurs regardless whether I call lookupTable->SetIndexedLookup(1) or not.
It feels somehow, as if the graph wouldn't care at all about my lookuptable. Am I doing something entirely wrong here ?

3)      In the code example above would it have been necessary to call lookupTable->Build() ? It doesn't seem to make a difference, when I try to omit it.

I would appreciate any help on this.
Thanks,
Daniel
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