Pick Operation Of vtkPropPicker On vtkSDL2OpenGLRenderWindow Is Not Working

Environment:
VTK Branch_v9.1.0
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.39

I tested two interfaces for pick operation of vtkPropPicker on web page. The result value is awalys 0.

int vtkPropPicker::Pick(double selectionX, double selectionY, double selectionZ,
           vtkRenderer *renderer) override;

int vtkPropPicker::PickProp(double selectionX, double selectionY, vtkRenderer *renderer);

Invoking code:

void Worker::OnLeftButtonDown()
{
    std::cout << "OnLeftButtonDown!\n";
    auto eventPos = m_RenderWindowInteractor->GetEventPosition();
    int ret = m_Picker->Pick( eventPos[0], eventPos[1], 0, m_Renderer );
    std::cout << "Pick: " << ret << std::endl;
    ret = m_Picker->PickProp( eventPos[0], eventPos[1], m_Renderer );
    std::cout << "PickProp: " << ret << std::endl;
    if( ret != 0 )
    {
        std::cout << "picked!\n";
    }
}

There are warning on browser log:

WebGL: INVALID_ENUM: readPixels: invalid format

[.WebGL-000073B40A41C000] GL_INVALID_OPERATION: Invalid format and type combination.

Maybe that’s a bug of VTK For WebAssembly. All source code has been uploaded to GitHub: https://github.com/theArcticOcean/tutorials/tree/main/learnWebAssembly/vtkPropPickerInWasm .