How to decrease mesh number while STEP to GLB file conversion?

Hello,

I am currently using Opencascade.js for converting STEP files to GLB format. But in a web viewer mesh number and draw calls are too high.

How can I reduce mesh number? I guess I need to change paramters of BRepMesh_IncrementalMesh_2 but I couldnt find the correct way.

I referenced this code:

https://draw.sview.ru/xde-export-step2gltf/

You cand find the code snippet below.

Thank you very much.

import fs from 'fs';
import path from 'path';
import initOpenCascade from 'opencascade.js/dist/node.js';




const loadSTEPorIGES = async (openCascade, file, fileName) => {

    const fileText = fs.readFileSync(file.path, 'utf8');

    const fileType = (() => {
        switch (fileName.toLowerCase().split(".").pop()) {
            case "step":
            case "stp":
                return "step";
            case "iges":
            case "igs":
                return "iges";
            default:
                return undefined;
        }
    })();
    // Writes the uploaded file to Emscripten's Virtual Filesystem
    openCascade.FS.createDataFile("/", `file.${fileType}`, fileText, true, true);

    // Choose the correct OpenCascade file parsers to read the CAD file
    var reader = null;
    if (fileType === "step") {
        reader = new openCascade.STEPCAFControl_Reader_1();
    } else if (fileType === "iges") {
        reader = new openCascade.IGESCAFControl_Reader_1();
    } else { console.error("opencascade.js can't parse this extension! (yet)"); }


    const readResult = reader.ReadFile(`file.${fileType}`);            // Read the file

    if (readResult === openCascade.IFSelect_ReturnStatus.IFSelect_RetDone) {
        console.log("file loaded successfully!     Converting to OCC now...");
        //const numRootsTransferred = reader.TransferRoots(new openCascade.Message_ProgressRange_1());    // Translate all transferable roots to OpenCascade

        // Create a document add our shapes
        const doc = new openCascade.TDocStd_Document(new openCascade.TCollection_ExtendedString_1());


        if (fileType === "step") {
            if (!reader.Transfer_1(new openCascade.Handle_TDocStd_Document_2(doc), new openCascade.Message_ProgressRange_1())) throw new Error();
        } else {
            if (!reader.Transfer(new openCascade.Handle_TDocStd_Document_2(doc), new openCascade.Message_ProgressRange_1())) throw new Error();

        }


        // Obtain the results of translation in one OCCT shape
        console.log(fileName + " converted successfully!  Triangulating now...");

        return visualizeShapes(openCascade, doc, fileName, fileType);

    } else {
        console.error("Something in OCCT went wrong trying to read " + fileName);
    }

};

function visualizeDoc(oc, doc, fileName, fileType) {

    const justName = path.parse(fileName).name;
    // Export a GLB file (this will also perform the meshing)
    const cafWriter = new oc.RWGltf_CafWriter(new oc.TCollection_AsciiString_2(`./${justName}.glb`), true);
    cafWriter.Perform_2(new oc.Handle_TDocStd_Document_2(doc), new oc.TColStd_IndexedDataMapOfStringString_1(), new oc.Message_ProgressRange_1());

    // Out with the old, in with the new!
    console.log(fileName + " triangulated and added to the scene!");

    // Remove the file when we're done (otherwise we run into errors on reupload)
    oc.FS.unlink(`/file.${fileType}`);
    // Read the GLB file from the virtual file system
    const glbFile = oc.FS.readFile(`./${justName}.glb`, { encoding: "binary" });
    const fileObj = { file: glbFile, filename: fileName };
    return fileObj;
}


function visualizeShapes(oc, doc, fileName, fileType) {


    const aRootLabels = new oc.TDF_LabelSequence_1();
    const aCompound = new oc.TopoDS_Compound();
    const shapeTool = oc.XCAFDoc_DocumentTool.ShapeTool(doc.Main()).get();

    shapeTool.GetFreeShapes(aRootLabels);

    const BRepBuilder = new oc.BRep_Builder();

    BRepBuilder.MakeCompound(aCompound);

    for (let i = 1; i <= aRootLabels.Length(); i++) {

        const aRootShape = new oc.TopoDS_Shape();
        const aRootLabel = aRootLabels.Value(i);


        if (oc.XCAFDoc_ShapeTool.GetShape_1(aRootLabel, aRootShape)) {
            BRepBuilder.Add(aCompound, aRootShape);
        }

    }

    const aDrawer = new oc.Prs3d_Drawer();

    const BoundBox = new oc.Bnd_Box_1();

    oc.BRepBndLib.Add(aCompound, BoundBox, false);

    const anAlgo = new oc.BRepMesh_IncrementalMesh_2(aCompound, oc.Prs3d.GetDeflection_2(BoundBox, aDrawer.MaximalChordialDeviation(), aDrawer.DeviationCoefficient()), false, (20.0 * Math.PI / 180.0), true);


    anAlgo.Perform_1(new oc.Message_ProgressRange_1());

    console.log("hey");
    // Return our visualized document
    return visualizeDoc(oc, doc, fileName, fileType);
}

const convertSTEPorIGES = async (file) => {

    const openCascade = await initOpenCascade();

    return loadSTEPorIGES(openCascade, file, file.filename);

}

export default convertSTEPorIGES;