In VTK, if the transparency of the image is modified, the depth value of the image will also change.

Support
1

In VTK, if the transparency of the image is modified, the depth value of the image will also change. Is there any way to keep the depth unchanged?

2

Which image actor class do you use? Does calling SetForceOpaque on the image actor help?

3

Thanks for your help,i use the vtkActor class.

4

And which mapper do you use?

5

vtkDataSetMapper

6

I’m not sure how vtkDataSetMapper maps vtkImageData. Using volume raycasting? Using surface rendering? Can you attach a few screenshots of how your rendering looks and illustrate what do you mean by different depth value?

8

Using surface rendering,vtkDataSetMapper can render the data of vtkimagedata . In fact, it is rendered the vtkStructuredGrid data.We have four pieces of data. When I set the transparency to {1,1,1,1}, the result is correct.We have four pieces of data. When I set the transparency to {1,1,1,1}, the result is correct. However, when I set the transparency to {0.6,1,1,1}, the result is not correct due to the depth value.

10 
int main( int argc, char *argv[] )

{

    if (argc < 2)

    {

      std::cout << "Required parameters: /YourPath" << std::endl;

      return -1;

    }

    

    vtkMPIController* mpiController = vtkMPIController::New();

    mpiController->Initialize( &argc, &argv );

    vtkMultiProcessController::SetGlobalController( mpiController );

    int rankId = mpiController->GetLocalProcessId();

    int numProcess = mpiController->GetNumberOfProcesses();

    

    if( numProcess > 4 )

    {

        std::cout << "error: numberOfProcess > numberOfBlock" << std::endl;

        return 0;

    }

    vtkRenderWindowInteractor* iren = vtkRenderWindowInteractor::New(); 

    vtkRenderWindow* renWin = vtkRenderWindow::New(); 

    vtkRenderer* render = vtkRenderer::New();

    iren->SetRenderWindow( renWin );

    renWin->AddRenderer( render );

    

    vtkTreeCompositer* compositer = vtkTreeCompositer::New();

    vtkCompositeRenderManager* parallelRender = vtkCompositeRenderManager::New(); 

    parallelRender->SetController( mpiController );

    parallelRender->SetRenderWindow( renWin );

    parallelRender->SetCompositer( compositer );

    compositer->Delete();

    double color[4][3] = { {1, 0, 0}, {0, 1, 0}, {0, 0, 1}, {1, 1, 0} };

    double opacity[4] = { 0.6, 1, 1, 1 }; 

    char* dataFilePath = argv[1]; 

    vtkPTecplotReaderBinary* reader = vtkPTecplotReaderBinary::New(); 

    reader->SetFileName(dataFilePath); 

    reader->Update();

    vtkMultiBlockDataSet* mbds = reader->GetOutput();

    int numBlock = mbds->GetNumberOfBlocks();

    int blocksLeft = 4 / numProcess;

    int res = 4 % numProcess;

    int count = rankId * blocksLeft;

    int index;

    for( int i = 0; i < numBlock; ++i )

    {

        vtkDataSetMapper* dsMapper = vtkDataSetMapper::New();

        dsMapper->SetInputDataObject( mbds->GetBlock( i ) );

        vtkActor* actor = vtkActor::New();

        actor->SetMapper( dsMapper );

        

        if( res )

        {

            index = rankId ? (count + i + 1) : (count + i);

        }

        else

        {

            index = count + i;

        }

        actor->GetProperty()->SetColor( color[index] );

        actor->GetProperty()->SetOpacity( opacity[index] );

        render->AddActor( actor );

        dsMapper->Delete();

        actor->Delete();

    }

    double bounds[6] = {2710, 44200, -2700, 2660, 548, 17800};

    render->ResetCamera( bounds );

    render->ResetCameraClippingRange( bounds );

    renWin->Delete();

    render->Delete();

        

    if( rankId )

    {

         parallelRender->InitializePieces();

         parallelRender->InitializeRMIs();

         mpiController->ProcessRMIs();

    }

    else

    {

        resetCameraCallback* callback = resetCameraCallback::New();

        callback->SetBounds( bounds );

        callback->SetRenderer( render );

        iren->AddObserver( vtkCommand::InteractionEvent, callback );

        renWin->SetSize( 600, 600 );

        renWin->Render();

        vtkInteractorStyleTrackballCamera* irenStyle2 = vtkInteractorStyleTrackballCamera::New();

        iren->SetInteractorStyle(irenStyle2);

        

        iren->Start();

    }

    

    return 0;

}
11

one
one852×478 17.5 KB
two

The red block is above the green block with a transparency of 0.6, but it does not display properly as shown in the results of the two images.I think it’s because the transparency has been changed, resulting in the change of image depth, so the result is not correct.

12

It seems that you haven’t enabled depth peeling. Without that, semi-transparent objects are not rendered correctly.

13

How can I enable depth peeling? Could you give me some advice? Thank you.

14

Search for “VTK depth peeling” on Google. You should be able to find documentation and examples.

15

Thank you！