propagate mobile swipe gestures to page where appropriate

src/perfect-scrollbar.js

@@ -28,6 +28,7 @@
   var defaultSettings = {
     wheelSpeed: 1,
     wheelPropagation: false,
+    swipePropagation: true,
     minScrollbarLength: null,
     maxScrollbarLength: null,
     useBothWheelAxes: false,
@@ -336,6 +337,33 @@
         return true;
       }
 
+      // check if default swipe should be prevented
+      function shouldPreventDefaultSwipe(deltaX, deltaY) {
+        var
+          scrollTop = $this.scrollTop(),
+          scrollLeft = $this.scrollLeft(),
+          magnitudeX = Math.abs(deltaX),
+          magnitudeY = Math.abs(deltaY);
+
+        if (magnitudeY > magnitudeX) {
+          // user is perhaps trying to swipe up/down the page
+
+          if (((deltaY < 0) && (scrollTop === contentHeight - containerHeight)) ||
+              ((deltaY > 0) && (scrollTop === 0))) {
+            return !settings.swipePropagation;
+          }
+        } else if (magnitudeX > magnitudeY) {
+          // user is perhaps trying to swipe left/right across the page
+
+          if (((deltaX < 0) && (scrollLeft === contentWidth - containerWidth)) ||
+              ((deltaX > 0) && (scrollLeft === 0))) {
+            return !settings.swipePropagation;
+          }
+        }
+
+        return true;
+      }
+
       function bindMouseWheelHandler() {
         var shouldPrevent = false;
 
@@ -713,10 +741,12 @@
               startTime = currentTime;
             }
 
+            if (shouldPreventDefaultSwipe(differenceX, differenceY)) {
               e.stopPropagation();
               e.preventDefault();
             }
           }
+        }
         function touchEnd(e) {
           if (!inGlobalTouch && inLocalTouch) {
             inLocalTouch = false;