[vtkusers] Create PolyData in vtk.js

[marf]

First off, thank you very much for your answer :-)

So my current state is, that I can render the data from a .vtu file as
polydata through using a mapper and an actor like this:

*const reader = xmlUnstructuredGridReader.newInstance();
const mapper = vtk.Rendering.Core.vtkMapper.newInstance({ scalarVisibility:
true });
const actor = vtk.Rendering.Core.vtkActor.newInstance();

await reader.parseAsArrayBuffer(serverFile);

actor.setMapper(mapper);
mapper.setInputConnection(reader.getOutputPort());

renderer.addActor(actor);
renderer.resetCamera();
this.onReady(renderWindow);

//UnstructuredGridReader is written by myself (with inspiration from the
vtkPolyDataReader) and utilizes the vtkXMLReader to read a .vtu file into a
polydataobject*


But now I also want to show more information, by coloring the model. I found
that this could by done by using a vtkLookupTable and tried the following,
before actor.setMapper(mapper)

*
const bounds = reader.getOutputData().getBounds();
const max = Math.max.apply(Math, bounds);
const min = Math.min.apply(Math, bounds);

const lookup = vtk.Common.Core.vtkLookupTable.newInstance();

lookup.setNumberOfColors(64),
lookup.setHueRange(0.0, 0.667);
lookup.setRange(min, max);
lookup.build();

mapper.setLookupTable(lookup);
mapper.setInterpolateScalarsBeforeMapping(true);
mapper.setUseLookupTableScalarRange(lookup);*


This did not do anything at all. So I treid coloring the point individually
kind of like this:

*for (let i = 0; i < pointsData.getNumberOfPoints(); i++) {
    const color = [];

    color[0] = 0.2;
    color[1] = 0.1;
    color[2] = 0.1;
    colors.insertNextTupleValue(color);
}

reader.getOutputData().getPointData().setScalars(colors);*


Since colors apparently should be a vtkUnsignedCharArray and that is not
implemented in vtkjs yet, I mocked it like this:

* 
const colors = {
    tupleValues: [ ],
    insertNextTupleValue: (color) => {
        for (let i = 0; i < color.length; i++) {
            colors.tupleValues.push(color[i]);
        }
    },
    getNumberOfComponents: () => {
        return 3;
    },
    getDataType: () => {
        return 'array';
    },
    getNumberOfTuples: () => {
        return colors.tupleValues.length / colors.getNumberOfComponents();
    },
    getData: () => {
        return colors.tupleValues;
    }
};
*


This actually lets me color the model, but there are some issues
- It will only ever pick up color[0] for a point, that can range from 0 ( =
orange-red) to 1 ( = blue) and misses a real red and all purple variations
- I have to kind of figure out the colors since rgb does not work at all
afaik
</ul>


Sorry for the very long post, I hope it is not even more confusing



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