Fix for overlapping edges

w8r/martinez#35

src/subdivide_segments.js

@@ -43,7 +43,7 @@ module.exports = function subdivide(eventQueue, subject, clipping, sbbox, cbbox,
       if (next) {
         if (possibleIntersection(event, next.key, eventQueue) === 2) {
           computeFields(event, prevEvent, operation);
-          computeFields(event, next.key, operation);
+          computeFields(next.key, event, operation);
         }
       }
 

test/edge_cases.test.js

@@ -243,5 +243,17 @@ tap.test('Edge cases', function(main) {
     t.end();
   });
 
+  main.test('overlapping edges difference', function (t) { // issue #35
+    const p1 = [ [ [0,0], [3,0], [3,3], [0,3], [0,0] ] ]
+    const p2 = [ [ [1,0], [2,0], [2,4], [1,4], [1,0] ] ]
+
+    var result = martinez.diff(p1, p2)
+    t.deepEqual(result, [
+      [[[0, 0], [1, 0], [1, 3], [0, 3], [0, 0]]],
+      [[[2, 0], [3, 0], [3, 3], [2, 3], [2, 0]]]
+    ])
+    t.end()
+  })
+
   main.end();
 });