STLFileSaver.js

/* 
Paul Kaplan, @ifitdidntwork

Create an ASCII STL file from a THREE.js mesh 
that can be saved save from browser and 3D printed
--------------------------------------------------
See further explanation here:
http://buildaweso.me/project/2013/2/25/converting-threejs-objects-to-stl-files
--------------------------------------------------
Saving the file out of the browser is done using FileSaver.js
find that here: https://github.com/eligrey/FileSaver.js
*/
function stringifyVector(vec){
  return ""+vec.x+" "+vec.y+" "+vec.z;
}

function stringifyVertex(vec){
  return "vertex "+stringifyVector(vec)+" \n";
}

// Given a THREE.Geometry, create an STL string
function generateSTL(geometry){
  var vertices = geometry.vertices;
  var tris     = geometry.faces;

  var stl = "solid model\n";
  for(var i = 0; i<tris.length; i++){
    stl += ("facet normal "+stringifyVector( tris[i].normal )+" \n");
    stl += ("outer loop \n");
    stl += stringifyVertex( vertices[ tris[i].a ] );
    stl += stringifyVertex( vertices[ tris[i].b ] );
    stl += stringifyVertex( vertices[ tris[i].c ] );
    stl += ("endloop \n");
    stl += ("endfacet \n");
  }
  stl += ("endsolid");

  return stl
}

// Use FileSaver.js 'saveAs' function to save the string
function saveSTL( geometry, name ){  
  var stlString = generateSTL( geometry );
  
  var blob = new Blob([stlString], {type: 'text/plain'});
  
  saveAs(blob, name + '.stl');
  
}