From a61688b517d0ec47b18d8bf53bcce262852949ff Mon Sep 17 00:00:00 2001
From: MurakamiShinyu <murakami@vivliostyle.org>
Date: Mon, 29 Oct 2018 04:49:18 +0900
Subject: [PATCH] prevent undesirable page swipe

---
 src/js/bindings/swipePages.js | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/js/bindings/swipePages.js b/src/js/bindings/swipePages.js
index 5f9bcd5..475d8f2 100644
--- a/src/js/bindings/swipePages.js
+++ b/src/js/bindings/swipePages.js
@@ -29,10 +29,23 @@ ko.bindingHandlers.swipePages = {
     init(element, valueAccessor) {
         if (supportTouchEvents && ko.unwrap(valueAccessor())) {
             element.addEventListener("touchstart", (event) => {
+                if (event.touches.length > 1) {
+                    return; // multi-touch is not for page swipe
+                }
+                if (window.visualViewport && window.visualViewport.scale > 1) {
+                    return; // disable page swipe when pinch-zoomed
+                }
+                const viewportElement = document.getElementById("vivliostyle-viewer-viewport");
+                if (viewportElement && viewportElement.scrollWidth > viewportElement.clientWidth) {
+                    return; // disable page swipe when horizontal scrollable
+                }
                 xStart = event.touches[0].clientX;                                      
                 yStart = event.touches[0].clientY;                                      
             });
             element.addEventListener("touchmove", (event) => {
+                if (event.touches.length > 1) {
+                    return;
+                }
                 if (xStart !== null && yStart !== null) {
                     let xDiff = event.touches[0].clientX - xStart;
                     let yDiff = event.touches[0].clientY - yStart;