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<div id="msg">
<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/286999">286999</a></dd>
<dt>Author</dt> <dd>timothy_horton@apple.com</dd>
<dt>Date</dt> <dd>2021-12-13 17:50:21 -0800 (Mon, 13 Dec 2021)</dd>
</dl>

<h3>Log Message</h3>
<pre>Momentum Event Dispatcher: Excessive "kick" at the beginning of scrolling (especially on 60fps displays)
https://bugs.webkit.org/show_bug.cgi?id=234279
<rdar://problem/86425321>

Reviewed by Simon Fraser.

* WebProcess/WebPage/MomentumEventDispatcher.cpp:
(WebKit::MomentumEventDispatcher::handleWheelEvent):
(WebKit::MomentumEventDispatcher::didStartMomentumPhase):
Instead of back-dating the animation to try to acquire a momentum-start
delta, pass the one we got from the event through, and start the animation
curve at momentum-start time. Also, critically, inset ourselves along
the curve by the amount of that initial delta (since the time starts now).

Tested at both 60fps and 120fps, this significantly smooths out the
transition from fingers-down phase to the generated momentum phase,
avoiding the overly large initial delta.

* WebProcess/WebPage/MomentumEventDispatcher.h:</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebKitChangeLog">trunk/Source/WebKit/ChangeLog</a></li>
<li><a href="#trunkSourceWebKitWebProcessWebPageMomentumEventDispatchercpp">trunk/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.cpp</a></li>
<li><a href="#trunkSourceWebKitWebProcessWebPageMomentumEventDispatcherh">trunk/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.h</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebKitChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit/ChangeLog (286998 => 286999)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit/ChangeLog    2021-12-14 01:38:11 UTC (rev 286998)
+++ trunk/Source/WebKit/ChangeLog       2021-12-14 01:50:21 UTC (rev 286999)
</span><span class="lines">@@ -1,3 +1,25 @@
</span><ins>+2021-12-13  Tim Horton  <timothy_horton@apple.com>
+
+        Momentum Event Dispatcher: Excessive "kick" at the beginning of scrolling (especially on 60fps displays)
+        https://bugs.webkit.org/show_bug.cgi?id=234279
+        <rdar://problem/86425321>
+
+        Reviewed by Simon Fraser.
+
+        * WebProcess/WebPage/MomentumEventDispatcher.cpp:
+        (WebKit::MomentumEventDispatcher::handleWheelEvent):
+        (WebKit::MomentumEventDispatcher::didStartMomentumPhase):
+        Instead of back-dating the animation to try to acquire a momentum-start
+        delta, pass the one we got from the event through, and start the animation
+        curve at momentum-start time. Also, critically, inset ourselves along
+        the curve by the amount of that initial delta (since the time starts now).
+
+        Tested at both 60fps and 120fps, this significantly smooths out the
+        transition from fingers-down phase to the generated momentum phase,
+        avoiding the overly large initial delta.
+
+        * WebProcess/WebPage/MomentumEventDispatcher.h:
+
</ins><span class="cx"> 2021-12-13  J Pascoe  <j_pascoe@apple.com>
</span><span class="cx"> 
</span><span class="cx">         [WebAuthn] Allow same-site, cross-origin iframe get()
</span></span></pre></div>
<a id="trunkSourceWebKitWebProcessWebPageMomentumEventDispatchercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.cpp (286998 => 286999)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.cpp       2021-12-14 01:38:11 UTC (rev 286998)
+++ trunk/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.cpp  2021-12-14 01:50:21 UTC (rev 286999)
</span><span class="lines">@@ -100,9 +100,6 @@
</span><span class="cx"> #endif
</span><span class="cx">     }
</span><span class="cx"> 
</span><del>-    if (event.phase() == WebWheelEvent::PhaseEnded)
-        m_lastEndedEventTimestamp = event.ioHIDEventTimestamp();
-
</del><span class="cx">     if (eventShouldStartSyntheticMomentumPhase(pageIdentifier, event))
</span><span class="cx">         didStartMomentumPhase(pageIdentifier, event);
</span><span class="cx"> 
</span><span class="lines">@@ -190,13 +187,11 @@
</span><span class="cx"> 
</span><span class="cx">     tracePoint(SyntheticMomentumStart);
</span><span class="cx"> 
</span><del>-    auto momentumStartInterval = event.ioHIDEventTimestamp() - m_lastEndedEventTimestamp;
-
</del><span class="cx">     m_currentGesture.active = true;
</span><span class="cx">     m_currentGesture.pageIdentifier = pageIdentifier;
</span><span class="cx">     m_currentGesture.initiatingEvent = event;
</span><span class="cx">     m_currentGesture.currentOffset = { };
</span><del>-    m_currentGesture.startTime = MonotonicTime::now() - momentumStartInterval;
</del><ins>+    m_currentGesture.startTime = MonotonicTime::now();
</ins><span class="cx">     m_currentGesture.displayNominalFrameRate = displayProperties->nominalFrameRate;
</span><span class="cx">     m_currentGesture.accelerationCurve = [&] () -> std::optional<ScrollingAccelerationCurve> {
</span><span class="cx">         auto curveIterator = m_accelerationCurves.find(m_currentGesture.pageIdentifier);
</span><span class="lines">@@ -213,7 +208,12 @@
</span><span class="cx">     float idealCurveMultiplier = m_currentGesture.accelerationCurve->frameRate() / idealCurveFrameRate;
</span><span class="cx">     buildOffsetTableWithInitialDelta(*event.rawPlatformDelta() * idealCurveMultiplier);
</span><span class="cx"> 
</span><del>-    dispatchSyntheticMomentumEvent(WebWheelEvent::PhaseBegan, consumeDeltaForCurrentTime());
</del><ins>+    WebCore::FloatSize consumedDelta = event.delta();
+    if (m_currentGesture.initiatingEvent->directionInvertedFromDevice())
+        consumedDelta.scale(-1);
+    m_currentGesture.currentOffset += consumedDelta;
+    
+    dispatchSyntheticMomentumEvent(WebWheelEvent::PhaseBegan, event.delta());
</ins><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> void MomentumEventDispatcher::didEndMomentumPhase()
</span></span></pre></div>
<a id="trunkSourceWebKitWebProcessWebPageMomentumEventDispatcherh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.h (286998 => 286999)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.h 2021-12-14 01:38:11 UTC (rev 286998)
+++ trunk/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.h    2021-12-14 01:50:21 UTC (rev 286999)
</span><span class="lines">@@ -123,7 +123,6 @@
</span><span class="cx">     HistoricalDeltas m_deltaHistoryY;
</span><span class="cx"> 
</span><span class="cx">     std::optional<WallTime> m_lastScrollTimestamp;
</span><del>-    WallTime m_lastEndedEventTimestamp;
</del><span class="cx">     std::optional<WebWheelEvent> m_lastIncomingEvent;
</span><span class="cx">     WebCore::RectEdges<bool> m_lastRubberBandableEdges;
</span><span class="cx"> 
</span></span></pre>
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