[vtkusers] RE : Newbie question: unstructuredGrid with voxels of different colours

[Teresa Azevedo]

Thanks for your answer, Mark.

I tried to use that function, using this code (build a 3x3x3 blue-red  
3D chessboard):

         int nbVoxels = 3*3*3;
         int voxelSize = 1;

         vtkPoints *voxelPoints = vtkPoints::New();
         voxelPoints->SetNumberOfPoints(8*nbVoxels);
         voxelPoints->SetDataTypeToDouble();

         vtkUnstructuredGrid *grid = vtkUnstructuredGrid::New();
         grid->Allocate(nbVoxels);

         vtkVoxel *voxel = vtkVoxel::New();
         int count = 0;
         int posX = 0;
         int posY = 0;
         int posZ = 0;
         for ( int v=0; v<nbVoxels ; v++ )
         {
                 voxelPoints->InsertPoint(count*8+0, posX,              
            posY,                        posZ);
                 voxelPoints->InsertPoint(count*8+1, posX+voxelSize,  
posY,                        posZ);
                 voxelPoints->InsertPoint(count*8+2, posX,              
            posY+voxelSize, posZ);
                 voxelPoints->InsertPoint(count*8+3, posX+voxelSize,  
posY+voxelSize, posZ);
                 voxelPoints->InsertPoint(count*8+4, posX,              
            posY,                        posZ+voxelSize);
                 voxelPoints->InsertPoint(count*8+5, posX+voxelSize,  
posY,                        posZ+voxelSize);
                 voxelPoints->InsertPoint(count*8+6, posX,              
            posY+voxelSize, posZ+voxelSize);
                 voxelPoints->InsertPoint(count*8+7, posX+voxelSize,  
posY+voxelSize, posZ+voxelSize);

                 voxel->GetPointIds()->SetId(0, count*8+0);
                 voxel->GetPointIds()->SetId(1, count*8+1);
                 voxel->GetPointIds()->SetId(2, count*8+2);
                 voxel->GetPointIds()->SetId(3, count*8+3);
                 voxel->GetPointIds()->SetId(4, count*8+4);
                 voxel->GetPointIds()->SetId(5, count*8+5);
                 voxel->GetPointIds()->SetId(6, count*8+6);
                 voxel->GetPointIds()->SetId(7, count*8+7);

                 grid->InsertNextCell(VTK_VOXEL, voxel->GetPointIds());
                 count++;

                 posX += voxelSize;
                 if ( posX == 3*voxelSize )
                 {
                         posX = 0;
                         posY += voxelSize;
                         if ( posY == 3*voxelSize )
                         {
                                 posY = 0;
                                 posZ += voxelSize;
                         }
                 }
         }
         grid->SetPoints(voxelPoints);

         //extract edges from unstructured grid
         vtkExtractEdges *edges = vtkExtractEdges::New();
         edges->SetInput(grid);

         vtkPolyDataMapper *gridMapper = vtkPolyDataMapper::New();
         gridMapper->SetInput(edges->GetOutput());

         vtkActor *gridActor = vtkActor::New();
         gridActor->SetMapper(gridMapper);
         gridActor->GetProperty()->SetColor(0.0,0.0,0.0);

         vtkDoubleArray *colourPts = vtkDoubleArray::New();
         for(int i=0; i < nbVoxels; i++)
                 colourPts->InsertNextValue(i);

         vtkCellData *cellData = grid->GetCellData();
         cellData->SetNumberOfTuples(nbVoxels);
         cellData->SetScalars(colourPts);

         //create a transfer function mapping scalar value to color
         vtkColorTransferFunction *fColor = vtkColorTransferFunction::New();
         for (int idx = 0; idx < nbVoxels; idx++)
         {
                 if (idx & 0x01)
                         fColor->AddRGBPoint(colourPts->GetValue(idx),  
1, 0, 0);
                 else
                         fColor->AddRGBPoint(colourPts->GetValue(idx),  
0, 0, 1);
         }

         //create a transfer function mapping scalar value to opacity
         vtkPiecewiseFunction *fOpacity = vtkPiecewiseFunction::New();
         fOpacity->AddPoint(0, 1);
         fOpacity->AddPoint(nbVoxels, 1);

         vtkVolumeProperty *volProp = vtkVolumeProperty::New();
         volProp->SetColor(fColor);
         volProp->SetScalarOpacity(fOpacity);

         // make sure we have only tetrahedra
         vtkDataSetTriangleFilter *filter = vtkDataSetTriangleFilter::New();
         filter->SetInput(grid);

         vtkUnstructuredGridVolumeRayCastMapper *vrcm =
vtkUnstructuredGridVolumeRayCastMapper::New();
         vrcm->SetInput(filter->GetOutput());

         vtkVolume *volume = vtkVolume::New();
         volume->SetMapper(vrcm);
         volume->SetProperty(volProp);

         // create a rendering window and renderer
         vtkRenderer *renderer = vtkRenderer::New();
         vtkRenderWindow *renderWindow = vtkRenderWindow::New();
         renderWindow->AddRenderer(renderer);

         vtkRenderWindowInteractor *iren = vtkRenderWindowInteractor::New();
     iren->SetRenderWindow(renderWindow);

         renderer->AddActor(volume);
         renderer->AddActor(gridActor);
         renderer->SetBackground(1,1,1);

         // interact with data
         renderWindow->Render();
         iren->Start();

The result is on the attached figure. As you can see both the opacity  
and colors are
wrong... but I do not know why...
Can someone please help me?

Teresa


Quoting Mark Jefferson <mark.jefferson at qq.com>:

> Hi, Teresa,
>    you can try class vtkColorTransferFunction. for example:
>  // Create a transfer function mapping scalar value to color (color)
>   vtkColorTransferFunction *cTFun = vtkColorTransferFunction::New();
>   cTFun->AddRGBPoint(   0, 1.0, 0.0, 0.0 );
>   cTFun->AddRGBPoint(  64, 1.0, 1.0, 0.0 );
>   cTFun->AddRGBPoint( 128, 0.0, 1.0, 0.0 );
>   cTFun->AddRGBPoint( 192, 0.0, 1.0, 1.0 );
>   cTFun->AddRGBPoint( 255, 0.0, 0.0, 1.0 );
>   hope this could help you.
>    M. J.

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