Remove includeOverlaps parameter from getCrossings()

And write better comments about how overlaps should be dealt with ideally.

src/path/PathItem.Boolean.js

@@ -92,9 +92,8 @@ PathItem.inject(new function() {
             _path2.reverse();
         // Split curves at crossings on both paths. Note that for self-
         // intersection, path2 is null and getIntersections() handles it.
-        var crossings = divideLocations(CurveLocation.expand(
-                // Only handle overlaps when not self-intersecting
-                _path1.getCrossings(_path2, !!_path2))),
+        var crossings = divideLocations(
+                CurveLocation.expand(_path1.getCrossings(_path2))),
             segments = [],
             // Aggregate of all curves in both operands, monotonic in y.
             monoCurves = [],
@@ -156,7 +155,7 @@ PathItem.inject(new function() {
             return null;
         var _path1 = preparePath(path1, false),
             _path2 = preparePath(path2, false),
-            crossings = _path1.getCrossings(_path2, true),
+            crossings = _path1.getCrossings(_path2),
             sub = operator.subtract,
             paths = [];
 

src/path/PathItem.js

@@ -146,16 +146,18 @@ var PathItem = Item.extend(/** @lends PathItem# */{
      * crossing each other, as opposed to simply touching.
      *
      * @param {PathItem} path the other item to find the crossings with
-     * @param {Boolean} includeOverlaps whether to also count overlaps as
-     *     crossings
      * @see #getIntersections(path)
      */
-    getCrossings: function(path, includeOverlaps) {
+    getCrossings: function(path) {
         return this.getIntersections(path, function(inter) {
             // TODO: Only return overlaps that are actually crossings! For this
-            // we need proper overlap range detection first.
-            // Check overlap first since it's the cheaper test between the two.
-            return includeOverlaps && inter._overlap || inter.isCrossing();
+            // we need proper overlap range detection / merging first...
+            // But as we call #resolveCrossings() first in boolean operations,
+            // removing all self-touching areas in paths, this currently works
+            // as it should in the known use cases.
+            // The ideal implementation would deal with it in a way outlined in:
+            // https://github.com/paperjs/paper.js/issues/874#issuecomment-168332391
+            return inter._overlap || inter.isCrossing();
         });
     },