From 1501ba5c0de88cb861077e68d78f96c933cfd2d8 Mon Sep 17 00:00:00 2001
From: Tobias Gutmann <tobias.gutmann@methodpark.de>
Date: Tue, 18 Jun 2019 10:43:33 +0200
Subject: [PATCH] fix(issue#935): Prevent WheelEvent from propagating

---
 src/eventListeners/wheelEventListener.js      |  7 +++++++
 src/eventListeners/wheelEventListener.test.js | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/src/eventListeners/wheelEventListener.js b/src/eventListeners/wheelEventListener.js
index 594d147c1..0fcab799a 100644
--- a/src/eventListeners/wheelEventListener.js
+++ b/src/eventListeners/wheelEventListener.js
@@ -23,6 +23,13 @@ function wheelEventHandler(evt) {
     return;
   }
 
+  // Prevent triggering MouseWheel events that are not real scroll events:
+  // E.g. when clicking the MiddleMouseWheelButton, a deltaY of 0 is emitted.
+  // See https://github.com/cornerstonejs/cornerstoneTools/issues/935
+  if (evt.deltaY > -1 && evt.deltaY < 1) {
+    return;
+  }
+
   evt.preventDefault();
 
   const { pageX, pageY } = evt;
diff --git a/src/eventListeners/wheelEventListener.test.js b/src/eventListeners/wheelEventListener.test.js
index 996e51e5e..50ab6068e 100644
--- a/src/eventListeners/wheelEventListener.test.js
+++ b/src/eventListeners/wheelEventListener.test.js
@@ -103,4 +103,23 @@ describe('eventListeners/wheelEventListener.js', () => {
     // Fire Away!
     localElement.dispatchEvent(new Event('wheel'));
   });
+
+  it('does not emit an `cornerstonetoolsmousewheel` event when scrolling less than one pixel', () => {
+    // Setup
+    const localElement = document.createElement('div');
+    const scrollCloseToZeroPixel = 0.00001;
+    const middleMouseButtonClickedEvent = new WheelEvent('wheel', { deltaY: scrollCloseToZeroPixel });
+
+    // Assert
+    localElement.addEventListener('cornerstonetoolsmousewheel', (evt) => {
+      expect(false).toBe(true, 'Unwanted event fired');
+    });
+
+    // SUT
+    wheelEventListener.enable(localElement);
+
+    // Fire Away!
+    localElement.dispatchEvent(middleMouseButtonClickedEvent);
+  });
+
 });