From 107a68cb1d12aa6ed74e4ca414e5f05e4a92c963 Mon Sep 17 00:00:00 2001
From: wolfbeast <mcwerewolf@gmail.com>
Date: Sat, 22 Dec 2018 06:30:39 +0100
Subject: Intersection ratio should be 1.0 for zero-area intersections.

Tag #249
---
 dom/base/DOMIntersectionObserver.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

(limited to 'dom/base')

diff --git a/dom/base/DOMIntersectionObserver.cpp b/dom/base/DOMIntersectionObserver.cpp
index cb624fb17..0834bc05c 100644
--- a/dom/base/DOMIntersectionObserver.cpp
+++ b/dom/base/DOMIntersectionObserver.cpp
@@ -411,7 +411,13 @@ DOMIntersectionObserver::Update(nsIDocument* aDocument, DOMHighResTimeStamp time
     double targetArea = targetRect.width * targetRect.height;
     double intersectionArea = !intersectionRect ?
       0 : intersectionRect->width * intersectionRect->height;
-    double intersectionRatio = targetArea > 0.0 ? intersectionArea / targetArea : 0.0;
+    
+    double intersectionRatio;
+    if (targetArea > 0.0) {
+      intersectionRatio = intersectionArea / targetArea;
+    } else {
+      intersectionRatio = intersectionRect.isSome() ? 1.0 : 0.0;
+    }
 
     size_t threshold = -1;
     if (intersectionRatio > 0.0) {
-- 
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