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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/287593">287593</a></dd>
<dt>Author</dt> <dd>simon.fraser@apple.com</dd>
<dt>Date</dt> <dd>2022-01-04 15:48:08 -0800 (Tue, 04 Jan 2022)</dd>
</dl>

<h3>Log Message</h3>
<pre>"canceled" wheel events to non-zero deltas cause scrolling jumps in PDFs and CodeMirror
https://bugs.webkit.org/show_bug.cgi?id=234825

Reviewed by Tim Horton.

Source/WebKit:

On some macOS versions, interrupting a momentum scroll via a two-finger tap on the trackpad can
result in the following sequence of wheel events: momentumPhase:end -> phase:mayBegin -> phase:cancelled,
and that last canceled event can have non-zero deltas (rdar://86653042).

Protect against this by zeroing out the deltas for cancelled wheel events when constructing WebEvents
from NSEvents. Code in Element::dispatchWheelEvent() ensures that we don't dispatch wheel events with
zero deltas to script, fixing CodeMirror.

Jumps only affected PDFs (and scrollable selects) because those are the code paths that don't go via
ScrollingEffectsController, which already ignores Cancelled events.

Test: fast/scrolling/mac/canceled-event-with-non-zero-deltas.html

* Shared/mac/WebEventFactory.mm:
(WebKit::WebEventFactory::createWebWheelEvent):

LayoutTests:

* fast/scrolling/mac/canceled-event-with-non-zero-deltas-expected.txt: Added.
* fast/scrolling/mac/canceled-event-with-non-zero-deltas.html: Added.</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsChangeLog">trunk/LayoutTests/ChangeLog</a></li>
<li><a href="#trunkSourceWebKitChangeLog">trunk/Source/WebKit/ChangeLog</a></li>
<li><a href="#trunkSourceWebKitSharedmacWebEventFactorymm">trunk/Source/WebKit/Shared/mac/WebEventFactory.mm</a></li>
</ul>

<h3>Added Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsfastscrollingmaccanceledeventwithnonzerodeltasexpectedtxt">trunk/LayoutTests/fast/scrolling/mac/canceled-event-with-non-zero-deltas-expected.txt</a></li>
<li><a href="#trunkLayoutTestsfastscrollingmaccanceledeventwithnonzerodeltashtml">trunk/LayoutTests/fast/scrolling/mac/canceled-event-with-non-zero-deltas.html</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkLayoutTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/LayoutTests/ChangeLog (287592 => 287593)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/ChangeLog      2022-01-04 23:31:23 UTC (rev 287592)
+++ trunk/LayoutTests/ChangeLog 2022-01-04 23:48:08 UTC (rev 287593)
</span><span class="lines">@@ -1,3 +1,13 @@
</span><ins>+2022-01-04  Simon Fraser  <simon.fraser@apple.com>
+
+        "canceled" wheel events to non-zero deltas cause scrolling jumps in PDFs and CodeMirror
+        https://bugs.webkit.org/show_bug.cgi?id=234825
+
+        Reviewed by Tim Horton.
+
+        * fast/scrolling/mac/canceled-event-with-non-zero-deltas-expected.txt: Added.
+        * fast/scrolling/mac/canceled-event-with-non-zero-deltas.html: Added.
+
</ins><span class="cx"> 2022-01-04  Devin Rousso  <drousso@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Web Inspector: Sources: expanding a grouping of blackboxed call frames should be persistent
</span></span></pre></div>
<a id="trunkLayoutTestsfastscrollingmaccanceledeventwithnonzerodeltasexpectedtxt"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/fast/scrolling/mac/canceled-event-with-non-zero-deltas-expected.txt (0 => 287593)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/fast/scrolling/mac/canceled-event-with-non-zero-deltas-expected.txt                            (rev 0)
+++ trunk/LayoutTests/fast/scrolling/mac/canceled-event-with-non-zero-deltas-expected.txt       2022-01-04 23:48:08 UTC (rev 287593)
</span><span class="lines">@@ -0,0 +1,9 @@
</span><ins>+wheel event deltaY 10
+wheel event deltaY 30
+wheel event deltaY 40
+wheel event deltaY 32
+wheel event deltaY 20
+PASS successfullyParsed is true
+
+TEST COMPLETE
+
</ins></span></pre></div>
<a id="trunkLayoutTestsfastscrollingmaccanceledeventwithnonzerodeltashtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/fast/scrolling/mac/canceled-event-with-non-zero-deltas.html (0 => 287593)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/fast/scrolling/mac/canceled-event-with-non-zero-deltas.html                            (rev 0)
+++ trunk/LayoutTests/fast/scrolling/mac/canceled-event-with-non-zero-deltas.html       2022-01-04 23:48:08 UTC (rev 287593)
</span><span class="lines">@@ -0,0 +1,82 @@
</span><ins>+<!DOCTYPE html>
+<html>
+<head>
+    <style>
+        body {
+            height: 2000px;
+            width: 200%;
+        }
+    </style>
+    <script src="../../../resources/js-test-pre.js"></script>
+    <script src="../../../resources/ui-helper.js"></script>
+    <script>
+        var jsTestIsAsync = true;
+
+        async function scrollTest()
+        {
+            const events = [
+                {
+                    type : "wheel",
+                    viewX : 100,
+                    viewY : 100,
+                    deltaY : -10,
+                    phase : "began"
+                },
+                {
+                    type : "wheel",
+                    deltaY : -30,
+                    phase : "changed"
+                },
+                {
+                    type : "wheel",
+                    phase : "ended"
+                },
+                {
+                    type : "wheel",
+                    deltaY : -40,
+                    momentumPhase : "began"
+                },
+                {
+                    type: "wheel",
+                    deltaY : -32,
+                    momentumPhase: "changed"
+                },
+                {
+                    type: "wheel",
+                    viewX : 101, // defeat coalescing
+                    deltaY : -20,
+                    momentumPhase: "changed"
+                },
+                {
+                    type: "wheel",
+                    momentumPhase: "ended"
+                },
+                {
+                    type: "wheel",
+                    phase: "maybegin"
+                },
+                {
+                    type: "wheel",
+                    deltaX : 10,
+                    deltaY : 100,
+                    phase: "cancelled"
+                }
+            ];
+
+            await UIHelper.mouseWheelSequence({ events });
+            finishJSTest();
+        }
+
+        window.addEventListener('load', () => {
+            window.addEventListener('wheel', (event) => {
+                debug('wheel event deltaY ' + event.deltaY);
+            }, { passive: true });
+
+            setTimeout(scrollTest, 0);
+        }, false);
+    </script>
+</head>
+<body>
+    <script src="../../../resources/js-test-post.js"></script>
+</body>
+</html>
</ins></span></pre></div>
<a id="trunkSourceWebKitChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit/ChangeLog (287592 => 287593)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit/ChangeLog    2022-01-04 23:31:23 UTC (rev 287592)
+++ trunk/Source/WebKit/ChangeLog       2022-01-04 23:48:08 UTC (rev 287593)
</span><span class="lines">@@ -1,3 +1,26 @@
</span><ins>+2022-01-04  Simon Fraser  <simon.fraser@apple.com>
+
+        "canceled" wheel events to non-zero deltas cause scrolling jumps in PDFs and CodeMirror
+        https://bugs.webkit.org/show_bug.cgi?id=234825
+
+        Reviewed by Tim Horton.
+
+        On some macOS versions, interrupting a momentum scroll via a two-finger tap on the trackpad can
+        result in the following sequence of wheel events: momentumPhase:end -> phase:mayBegin -> phase:cancelled,
+        and that last canceled event can have non-zero deltas (rdar://86653042).
+
+        Protect against this by zeroing out the deltas for cancelled wheel events when constructing WebEvents
+        from NSEvents. Code in Element::dispatchWheelEvent() ensures that we don't dispatch wheel events with
+        zero deltas to script, fixing CodeMirror.
+
+        Jumps only affected PDFs (and scrollable selects) because those are the code paths that don't go via
+        ScrollingEffectsController, which already ignores Cancelled events.
+
+        Test: fast/scrolling/mac/canceled-event-with-non-zero-deltas.html
+
+        * Shared/mac/WebEventFactory.mm:
+        (WebKit::WebEventFactory::createWebWheelEvent):
+
</ins><span class="cx"> 2022-01-04  Wenson Hsieh  <wenson_hsieh@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Use ICU instead of relying on hard-coded string equality checks in ModalContainerControlClassifier
</span></span></pre></div>
<a id="trunkSourceWebKitSharedmacWebEventFactorymm"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit/Shared/mac/WebEventFactory.mm (287592 => 287593)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit/Shared/mac/WebEventFactory.mm        2022-01-04 23:31:23 UTC (rev 287592)
+++ trunk/Source/WebKit/Shared/mac/WebEventFactory.mm   2022-01-04 23:48:08 UTC (rev 287593)
</span><span class="lines">@@ -438,6 +438,15 @@
</span><span class="cx"> 
</span><span class="cx">     auto ioHIDEventWallTime = WebCore::eventTimeStampSince1970(ioHIDEventTimestamp);
</span><span class="cx"> 
</span><ins>+    if (phase == WebWheelEvent::PhaseCancelled) {
+        deltaX = 0;
+        deltaY = 0;
+        wheelTicksX = 0;
+        wheelTicksY = 0;
+        unacceleratedScrollingDelta = { };
+        rawPlatformDelta = std::nullopt;
+    }
+
</ins><span class="cx">     return WebWheelEvent(WebEvent::Wheel, WebCore::IntPoint(position), WebCore::IntPoint(globalPosition), WebCore::FloatSize(deltaX, deltaY), WebCore::FloatSize(wheelTicksX, wheelTicksY),
</span><span class="cx">         granularity, directionInvertedFromDevice, phase, momentumPhase, hasPreciseScrollingDeltas,
</span><span class="cx">         scrollCount, unacceleratedScrollingDelta, modifiers, timestamp, ioHIDEventWallTime, rawPlatformDelta);
</span></span></pre>
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