Move overscroll logic out of EventHandler.

third_party/WebKit/Source/core/page/scrolling/OverscrollController.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/page/scrolling/OverscrollController.h"
+
+#include "core/frame/VisualViewport.h"
+#include "core/page/ChromeClient.h"
+#include "platform/geometry/FloatPoint.h"
+#include "platform/geometry/FloatSize.h"
+#include "platform/scroll/ScrollTypes.h"
+
+namespace blink {
+
+namespace {
+
+// Report Overscroll if OverscrollDelta is greater than minimumOverscrollDelta
+// to maintain consistency as done in the compositor.
+const float minimumOverscrollDelta = 0.1;
+
+void adjustOverscroll(FloatSize* unusedDelta)
+{
+    DCHECK(unusedDelta);
+    if (std::abs(unusedDelta->width()) < minimumOverscrollDelta)
+        unusedDelta->setWidth(0);
+    if (std::abs(unusedDelta->height()) < minimumOverscrollDelta)
+        unusedDelta->setHeight(0);
+}
+
+} // namespace
+
+OverscrollController::OverscrollController(
+    const VisualViewport& visualViewport, ChromeClient& chromeClient)
+    : m_visualViewport(&visualViewport)
+    , m_chromeClient(&chromeClient)
+{
+}
+
+DEFINE_TRACE(OverscrollController)
+{
+    visitor->trace(m_visualViewport);
+    visitor->trace(m_chromeClient);
+}
+
+void OverscrollController::resetAccumulated(
+    bool resetX, bool resetY)
+{
+    if (resetX)
+        m_accumulatedRootOverscroll.setWidth(0);
+    if (resetY)
+        m_accumulatedRootOverscroll.setHeight(0);
+}
+
+void OverscrollController::handleOverscroll(
+    const ScrollResult& scrollResult,
+    const FloatPoint& positionInRootFrame,
+    const FloatSize& velocityInRootFrame)
+{
+    DCHECK(m_visualViewport);
+    DCHECK(m_chromeClient);
+
+    FloatSize unusedDelta(
+        scrollResult.unusedScrollDeltaX,
+        scrollResult.unusedScrollDeltaY);
+    adjustOverscroll(&unusedDelta);
+
+    FloatSize deltaInViewport = unusedDelta.scaledBy(m_visualViewport->scale());
+    FloatSize velocityInViewport =
+        velocityInRootFrame.scaledBy(m_visualViewport->scale());
+    FloatPoint positionInViewport =
+        m_visualViewport->rootFrameToViewport(positionInRootFrame);
+
+    resetAccumulated(scrollResult.didScrollX, scrollResult.didScrollY);
+
+    if (deltaInViewport != FloatSize()) {
+        m_accumulatedRootOverscroll += deltaInViewport;
+        m_chromeClient->didOverscroll(
+            deltaInViewport,
+            m_accumulatedRootOverscroll,
+            positionInViewport,
+            velocityInViewport);
+    }
+}
+
+} // namespace blink