From 831c06c49919c9c2ef6faadf47cf5de59505b914 Mon Sep 17 00:00:00 2001
From: SangYeob Yu <syyu@lunit.io>
Date: Tue, 10 Dec 2019 16:29:20 +0900
Subject: [PATCH] fix iPadOS 13 multi-touch issue

---
 src/mousetracker.js | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/mousetracker.js b/src/mousetracker.js
index 8a342d18..396ea6ca 100644
--- a/src/mousetracker.js
+++ b/src/mousetracker.js
@@ -2661,7 +2661,7 @@
                     {
                         eventSource:          tracker,
                         pointerType:          curGPoint.type,
-                        position:             getPointRelativeToAbsolute( curGPoint.currentPos, tracker.element ),
+                        position:             curGPoint.currentPos && getPointRelativeToAbsolute( curGPoint.currentPos, tracker.element ),
                         buttons:              pointsList.buttons,
                         pointers:             tracker.getActivePointerCount(),
                         insideElementPressed: updateGPoint ? updateGPoint.insideElementPressed : false,
@@ -2958,10 +2958,16 @@
             return false;
         }
 
+        // OS-specific gestures (e.g. swipe up with four fingers in iPadOS 13)
+        if (gPoints[ 0 ].type === "touch" && typeof gPoints[ 0 ].currentPos === "undefined") {
+            abortContacts(tracker, event, pointsList);
+
+            return false;
+        }
+
         for ( i = 0; i < gPointCount; i++ ) {
             curGPoint = gPoints[ i ];
             updateGPoint = pointsList.getById( curGPoint.id );
-
             if ( updateGPoint ) {
                 // Update the pointer, stop tracking it if not still in this element
                 if ( updateGPoint.captured ) {