larsberg · March 23, 2016 17:51 · Mar 23, 2016
diff --git a/getWingedEdges.js b/getWingedEdges.js
@@ -0,0 +1,84 @@
+'use strict'
+
+var getWingedEdges = function( g ){
+
+  var edgeMap = {};
+
+  // find the edges
+  function getEdgeKey( i0, i1 ){
+    return Math.min(i0, i1) + '_' + Math.max(i0, i1);
+  }
+
+  function addEdge( i0, i1, faceIndex ){
+
+    var edgeKey = getEdgeKey( i0, i1 );
+
+    if(edgeMap[ edgeKey ] !== undefined){
+
+      edgeMap[ edgeKey ].f.push( faceIndex );
+
+    } else {
+
+      edgeMap[ edgeKey ] = {
+        v: [i0, i1],
+        f: [faceIndex],
+        normal: new THREE.Vector3()
+      }
+
+    }
+
+    return edgeKey;    
+  }
+
+  g.faces.forEach( function( f, i ){
+
+    addEdge(f.a, f.b, i);
+    addEdge(f.b, f.c, i);
+    addEdge(f.c, f.a, i);
+
+  });
+
+  // compute edge normals
+  g.computeFaceNormals();
+
+  function normalFromTwoVector( v0, v1 ){
+    return v0.cross( v1 ).normalize();
+  }
+
+  var v = g.vertices;
+  for(var i in edgeMap){
+
+    var e = edgeMap[i];
+
+    if(e.f.length > 1){
+
+      // average the face normals
+      var n = e.normal.set(0,0,0);
+
+      e.f.forEach( function( i ){
+
+        n.add( g.faces[i].normal );
+
+      });
+
+      n.divideScalar( e.f.length );
+
+    } else {
+
+      var f = g.faces[ e.f[0] ];
+
+      var v0 = f.normal.normalize().clone();
+
+      var v1 = v[ e.v[0] ].clone().sub( v[ e.v[1] ] ).normalize();
+
+      e.normal.copy( normalFromTwoVector( v0, v1 ) );
+    }
+
+  }
+
+  return edgeMap
+}
+
+
+module.exports = getWingedEdges;
+