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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/287031">287031</a></dd>
<dt>Author</dt> <dd>alancoon@apple.com</dd>
<dt>Date</dt> <dd>2021-12-14 10:30:27 -0800 (Tue, 14 Dec 2021)</dd>
</dl>

<h3>Log Message</h3>
<pre>Cherry-pick <a href="http://trac.webkit.org/projects/webkit/changeset/286999">r286999</a>. rdar://problem/86425321

    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:

    git-svn-id: https://svn.webkit.org/repository/webkit/trunk@286999 268f45cc-cd09-0410-ab3c-d52691b4dbfc</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#branchessafari612branchSourceWebKitChangeLog">branches/safari-612-branch/Source/WebKit/ChangeLog</a></li>
<li><a href="#branchessafari612branchSourceWebKitWebProcessWebPageMomentumEventDispatchercpp">branches/safari-612-branch/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.cpp</a></li>
<li><a href="#branchessafari612branchSourceWebKitWebProcessWebPageMomentumEventDispatcherh">branches/safari-612-branch/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.h</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="branchessafari612branchSourceWebKitChangeLog"></a>
<div class="modfile"><h4>Modified: branches/safari-612-branch/Source/WebKit/ChangeLog (287030 => 287031)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-612-branch/Source/WebKit/ChangeLog       2021-12-14 18:20:24 UTC (rev 287030)
+++ branches/safari-612-branch/Source/WebKit/ChangeLog  2021-12-14 18:30:27 UTC (rev 287031)
</span><span class="lines">@@ -1,3 +1,52 @@
</span><ins>+2021-12-14  Alan Coon  <alancoon@apple.com>
+
+        Cherry-pick r286999. rdar://problem/86425321
+
+    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:
+    
+    
+    git-svn-id: https://svn.webkit.org/repository/webkit/trunk@286999 268f45cc-cd09-0410-ab3c-d52691b4dbfc
+
+    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  Alan Coon  <alancoon@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Cherry-pick r286919. rdar://problem/86247557
</span></span></pre></div>
<a id="branchessafari612branchSourceWebKitWebProcessWebPageMomentumEventDispatchercpp"></a>
<div class="modfile"><h4>Modified: branches/safari-612-branch/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.cpp (287030 => 287031)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-612-branch/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.cpp  2021-12-14 18:20:24 UTC (rev 287030)
+++ branches/safari-612-branch/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.cpp     2021-12-14 18:30:27 UTC (rev 287031)
</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="branchessafari612branchSourceWebKitWebProcessWebPageMomentumEventDispatcherh"></a>
<div class="modfile"><h4>Modified: branches/safari-612-branch/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.h (287030 => 287031)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-612-branch/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.h    2021-12-14 18:20:24 UTC (rev 287030)
+++ branches/safari-612-branch/Source/WebKit/WebProcess/WebPage/MomentumEventDispatcher.h       2021-12-14 18:30:27 UTC (rev 287031)
</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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