Trouble exporting Scene to .vtkjs

Dear All,

Using the xml plugin from Point labels available with PV 5.7? - #7 by jourdain, we were able to add text labels to a point cloud in ParaView (Nightly on Mac).

Now, we would like to export the scene to a .vtkjs file to finally allow our colleagues a quick inspection in the vtk Scene Explorer.

Unfortunately, as soon as the Label Representation is selected for our data, the following error message appears upon .vtkjs-export:

Generic Warning: In vtkPVWebExporter.cxx, line 71
Failed to rename datasets using ParaView proxy name

Traceback (most recent call last):
  File "/Applications/", line 77, in applyParaViewNaming
    renameMap = getRenameMap()
  File "/Applications/", line 36, in getRenameMap
    names = getAllNames()
  File "/Applications/", line 26, in getAllNames
    actorRep = vtkRepInstance.GetActiveRepresentation().GetActor()
AttributeError: 'paraview.modules.vtkRemotingViews.vtkDataLabelRepr' object has no attribute 'GetActor'

Do you have any idea what we can do about this? Thank you :slight_smile:

Unfortunately I don’t think we have yet an implementation of those 3D labels in vtk.js.
But once we do, we will need to extend some code in VTK/ParaView to properly handle those object in the scene so they can be exported and displayed in vtk.js.

Maybe @martink or @Forrest_Li may know better the status of vtk.js on those text labels.


We do not have a point label class yet on the JS side.

But …you can sort of do what you want with a bit of code like this example

but it isn’t a direct in/out from paraview. But I think it is possible with some JS side coding.

Actually @martink suggestion is really good. You could export from ParaView just the pointset with the string array attached to it and have a custom vtk.js scene viewer that will do the same labels technique as that example.

The only caveat I see is that the PV exporter may currently skip non numerical array but that should be easy to fix/extend. And the JS code required to do such viewer will be pretty minimal and quick.

Hi @martink , @jourdain ,
thank you for your suggestions and sorry for not coming back to the topic earlier - I needed a while to learn at least some basics of javascript, npm, webpack, etc. to get things running :slight_smile:

Slightly inspired by SceneExplorerWidget.js, I put together the following LabelWidget.js:

import vtkPixelSpaceCallbackMapper from '@kitware/vtk.js/Rendering/Core/PixelSpaceCallbackMapper';
import vtkActor from '@kitware/vtk.js/Rendering/Core/Actor';

export default function addWidget(renderer, container, sceneItems, render) {

    let dims = null;

    const textCanvas = document.createElement('canvas');
    textCanvas.classList.add('labelCanvas'); = 'absolute'; = '0px'; = '0px'; = '100%'; = '100%'; = 'hidden';

    const textCtx = textCanvas.getContext('2d');

    window.addEventListener('resize', () => {
        dims = container.getBoundingClientRect();
        textCanvas.setAttribute('width', dims.width);
        textCanvas.setAttribute('height', dims.height);

    window.dispatchEvent(new Event("resize"));

    function getArrayNames(sceneItem) {
        return `<option value="0">---</option>`
            + sceneItem.source.getArrays()
                // introduced "+1" in array index, so that "0" means "no labels"
                .map((array, idx) => `<option value="${idx+1}">${}</option>`)

    const listStr = sceneItems
        (item, idx) =>
            `<li><select name="${idx}">${getArrayNames(item)}</select>&nbsp;&nbsp;${}</li>`

    const listContainer = document.createElement('ul');
    listContainer.innerHTML = listStr; = 'absolute'; = '25px'; = '100px'; = 'white'; = '5px'; = 'none'; = '5px 10px'; = '0'; = 'block'; = 'solid 1px black';


    document.querySelector('body').addEventListener('keypress', (e) => {
      if (String.fromCharCode(e.charCode) === 'l') {
        if ( === 'none') {
 = 'block';
        } else {
 = 'none';

    const selectList = listContainer.querySelectorAll('select');
    for (let i = 0; i < selectList.length; i++) {
      const selectElem = selectList[i];
      selectElem.addEventListener('change', handleChange);

    function handleChange(e) {
        const itemIdx = Number(;
        const value = Number(;
        // ugly hack: we just append an attribute to the sceneItem
        sceneItems[itemIdx].labelArray = value;
        if (render) {

    for (const sceneItem of sceneItems) {
       console.log(`Adding labels to ${}`)

        const psMapper = vtkPixelSpaceCallbackMapper.newInstance();
        psMapper.setCallback((coordsList) => {
        if (textCtx && dims) {
            textCtx.clearRect(0, 0, dims.width, dims.height);

            const labelArray = sceneItem.labelArray;

            if (labelArray) {
                coordsList.forEach((xy, idx) => {
                    textCtx.font = '12px serif';
                    textCtx.textAlign = 'center';
                    textCtx.textBaseline = 'middle';
                        // "-1" to compensate for offset introduced in getArrays()
                        // pixel ratio scaling from
                        xy[0] / window.devicePixelRatio,
                        dims.height - xy[1] / window.devicePixelRatio);
                    });            }

        const textActor = vtkActor.newInstance();

which can be instantiated in the onReady() function of the SceneExplorer via

import labelWidget from './LabelWidget';

        // Add UI to enable labels for different scene items

Now, I can conveniently select, for which sceneItems I want to see labels at the respective vtkPoints and which data array entries are to be printed (very messy here, this is not the original data):

Missing point is now, to also export the non-numeric point data arrays from Paraview into the *.vtkjs file.

Do you possibly have suggestions where I could start with this?

You will have to fix that class and the Array one to support the vtkAbstractArray/vtkStringArray.

Ouch, seeing C++ here does that mean I‘d have to build Paraview myself? - Did that years ago on Linux, but today I‘m on a corporate Windows machine with virtually no permissions…

Would there be an option with Python scripting in Paraview?

You might be able to do most of it in Python but you will have to use a macro to do the export.

A while back that export was 100% python rather than C++. You could revive that path to fix it, at least locally. But to make it mainstream, it will have to happen on the C++ side down the road.


Thank you for that hint @jourdain,
I looked into that macro, was able to make it run by fixing some stuff) and also extended it to export all numeric point data instead of only the __CustomRGBColorArray__.

I also understood, where I would need to add code to support vtkStringArray. However, as there does not seem to exist any typed arrays (see JavaScript typed arrays - JavaScript | MDN) for strings in JavaScript, I do not know in which form the string data would need to be written to be understood by the *.vtkjs reader of vtk.js.

These questions possibly also go to @martink: Does the *.vtkjs file format support string arrays? Is there any documentation on the file format of the reader code available somewhere?

Some more progress: Apparently, the *.vtkjs file format supports string arrays. They need to be written as UTF-8-encoded (UTF-16 might also work, but Python seems to insist on adding a BOM with vtk.js does not like) string that contains a JSON array of strings.

To achieve this besides some logistics changes here and there, I added the following at vtk-js/ at 6ae17f80c8496191d5439eaf746eac772a40450b · Kitware/vtk-js · GitHub

  elif array.GetDataType() == 13:
    # vtkStringArray - write as utf-8 encoded string that contains a json array with the strings
    arraySize = array.GetNumberOfTuples() * array.GetNumberOfComponents()
    newArray = json.dumps([array.GetValue(v) for v in range(arraySize)])
    pBuffer = memoryview(newArray.encode('utf-8'))

I’ll see if I can get some more rough corners ironed out and then will post the full solution here in case someone else also needs this.

Hi @jourdain, @martink,

Thanks to your support finally, everything is in place and works as expected with a modified export-scene-macro, I can export my scene including string arrays that contain label text and with a modified SceneExplorer, I can now select for all scene items which of them are to be labelled with data from which array.

Again: Thanks a lot for your support - wouldn’t have worked without your hints.

P.S.: Discussing how to proceed with the modified macro here. Not sure if the modified SceneExplorer would also be interesting for others…

1 Like