STL2SCAD.js - Optimizing decompiler of a binary STL into the OpenSCAD source

stl2scad.js

/**
 * Optimizing decompiler of a binary STL into the OpenSCAD polyhedron module
 * @license Unlicense
 *
 * @param {ArrayBuffer} stl STL file contents (binary flavor) 
 * @param {string} optional custom name for OpenSCAD object (if none passed then 'object{NumTriangles}' will be used)
 * @returns {string} ready OpenSCAD script
 */
function STL2SCAD(stl, optModName = null) {
    var totalTriangles = new Uint32Array(stl.slice(80, 84))[0], //triangle amount is LE uint at byte 80
        cVD = new Uint8Array(stl.slice(84)), //points should start from byte 84
        i, k, l = cVD.length, p, pKey, vertices = [], triangles = [],
        modName = optModName || ('object' + totalTriangles),
        embrace = a => '[' + a.join(', ') + ']',
        reslice = (i, k) => new Float32Array(cVD.slice(i+k+12, i+k+16).buffer)[0].toFixed(5) + 0,
        vertexCache = {}, triangle

    //trim the garbage
    if(l > totalTriangles * 50)
        l = totalTriangles * 50
        
    for(i=0;i<l;i+=50) { //two loops to skip all unused bytes
        triangle = []
        for(k=0;k<3;k++) {
            p = {
                x: reslice(i, 12*k),
                y: reslice(i, 12*k + 4),
                z: reslice(i, 12*k + 8)
            }
            pKey = [p.x, p.y, p.z].join(':')
            if(!vertexCache[pKey]) {
                vertices.push(embrace([p.x,p.y,p.z]))
                vertexCache[pKey] = vertices.length - 1
            }
            triangle.push(vertexCache[pKey])
        }
        triangles.push(embrace([triangle[0], triangle[2], triangle[1]]))
    }

    return 'module ' + modName + ' () {\n\tpolyhedron(\n\t\tpoints='
        + embrace(vertices) + ',\n\t\tfaces='
        + embrace(triangles) + '\n\t);\n}\n' + modName + '();'
}

if(module) {
    module.exports = STL2SCAD
    if(typeof require !== 'undefined' && require.main === module) {
        const fs = require('fs')
        let stlContents = fs.readFileSync(process.argv[2])
        console.log(STL2SCAD(stlContents.buffer))
    }
}