Implement support for clip-masks in hit-testing.

Closes #671

src/item/Group.js

@@ -167,6 +167,12 @@ var Group = Item.extend(/** @lends Group# */{
             child.setClipMask(clipped);
     },
 
+    _hitTestChildren: function _hitTestChildren(point, options) {
+        var clipItem = this._getClipItem();
+        return (!clipItem || clipItem.contains(point))
+                && _hitTestChildren.base.call(this, point, options, clipItem);
+    },
+
     _draw: function(ctx, param) {
         var clip = param.clip,
             clipItem = !clip && this._getClipItem();

src/item/Item.js

@@ -1836,12 +1836,14 @@ new function() { // // Scope to inject various item event handlers
         return res;
     },
 
-    _hitTestChildren: function(point, options) {
+    _hitTestChildren: function(point, options, _exclude) {
+        // NOTE: _exclude is only used in Group#_hitTestChildren()
         var children = this._children;
         if (children) {
             // Loop backwards, so items that get drawn last are tested first
             for (var i = children.length - 1; i >= 0; i--) {
-                var res = children[i]._hitTest(point, options);
+                var child = children[i];
+                var res = child !== _exclude && child._hitTest(point, options);
                 if (res)
                     return res;
             }

test/tests/HitResult.js

@@ -684,7 +684,7 @@ test('hit-testing compound-paths', function() {
         var result = paper.project.hitTest(center, {
             fill: true
         });
-        return result === null  ;
+        return result === null;
     }, true);
     // When asking specifically for paths, she should get the top-most path in
     // the center (the one that cuts out the hole)
@@ -697,5 +697,35 @@ test('hit-testing compound-paths', function() {
     }, true);
 });
 
+test('hit-testing clipped items', function() {
+    var rect = new Path.Rectangle({
+        point: [50, 150],
+        size: [100, 50],
+        fillColor: 'red'
+    });
+    var circle = new Path.Circle({
+        center: [100, 200],
+        radius: 20,
+        fillColor: 'green'
+    });
+    var group = new Group({
+        children: [rect, circle]
+    });
+    group.clipped = true;
+
+    var point1 = new Point(100, 190);
+    var point2 = new Point(100, 210);
+
+    equals(function() {
+        var result = paper.project.hitTest(point1);
+        return result && result.item === circle;
+    }, true);
+
+    equals(function() {
+        var result = paper.project.hitTest(point2);
+        return result === null;
+    }, true);
+});
+
 // TODO: project.hitTest(point, {type: AnItemType});