Implement a Hit Test Cache.

Source/core/layout/LayoutView.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 44 matching lines @@
     , m_selectionStart(nullptr)
     , m_selectionEnd(nullptr)
     , m_selectionStartPos(-1)
     , m_selectionEndPos(-1)
     , m_pageLogicalHeight(0)
     , m_pageLogicalHeightChanged(false)
     , m_layoutState(nullptr)
     , m_layoutQuoteHead(nullptr)
     , m_layoutCounterCount(0)
     , m_hitTestCount(0)
+    , m_hitTestCacheHits(0)
+    , m_hitTestCache(HitTestCache::create())
     , m_pendingSelection(PendingSelection::create())
 {
     // init LayoutObject attributes
     setInline(false);
 
     m_minPreferredLogicalWidth = 0;
     m_maxPreferredLogicalWidth = 0;
 
     setPreferredLogicalWidthsDirty(MarkOnlyThis);
 
     setPositionState(AbsolutePosition); // to 0,0 :)
 }
 
 LayoutView::~LayoutView()
 {
 }
 
 bool LayoutView::hitTest(HitTestResult& result)
 {
-    return hitTest(result.hitTestRequest(), result.hitTestLocation(), result);
-}
-
-bool LayoutView::hitTest(const HitTestRequest& request, const HitTestLocation& location, HitTestResult& result)
-{
     TRACE_EVENT_BEGIN0("blink,devtools.timeline", "HitTest");
     m_hitTestCount++;
 
-    ASSERT(!location.isRectBasedTest() || request.listBased());
+    ASSERT(!result.hitTestLocation().isRectBasedTest() || result.hitTestRequest().listBased());
 
     // We have to recursively update layout/style here because otherwise, when the hit test recurses
     // into a child document, it could trigger a layout on the parent document, which can destroy DeprecatedPaintLayer
     // that are higher up in the call stack, leading to crashes.
     // Note that Document::updateLayout calls its parent's updateLayout.
     // FIXME: It should be the caller's responsibility to ensure an up-to-date layout.
     frameView()->updateLayoutAndStyleForPainting();
     commitPendingSelection();
 
-    bool hitLayer = layer()->hitTest(request, location, result);
+    uint64_t domTreeVersion = document().domTreeVersion();
+    HitTestResult cacheResult = result;
+    bool cacheHit = m_hitTestCache->lookupCachedResult(cacheResult, domTreeVersion);
+    bool hitLayer = layer()->hitTest(result);
 
     // FrameView scrollbars are not the same as Layer scrollbars tested by Layer::hitTestOverflowControls,
     // so we need to test FrameView scrollbars separately here. Note that it's important we do this after
     // the hit test above, because that may overwrite the entire HitTestResult when it finds a hit.
-    IntPoint framePoint = frameView()->contentsToFrame(location.roundedPoint());
+    IntPoint framePoint = frameView()->contentsToFrame(result.hitTestLocation().roundedPoint());
     if (Scrollbar* frameScrollbar = frameView()->scrollbarAtFramePoint(framePoint))
         result.setScrollbar(frameScrollbar);
 
-    TRACE_EVENT_END1("blink,devtools.timeline", "HitTest", "endData", InspectorHitTestEvent::endData(request, location, result));
+    if (cacheHit) {
+        m_hitTestCacheHits++;
+        m_hitTestCache->verifyCachedResult(result, cacheResult);
+    }
+
+    if (hitLayer)
+        m_hitTestCache->addCachedResult(result, domTreeVersion);
+
+    TRACE_EVENT_END1("blink,devtools.timeline", "HitTest", "endData", InspectorHitTestEvent::endData(result.hitTestRequest(), result.hitTestLocation(), result));
     return hitLayer;
 }
 
 void LayoutView::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit, LogicalExtentComputedValues& computedValues) const
 {
     computedValues.m_extent = (!shouldUsePrintingLayout() && m_frameView) ? LayoutUnit(viewLogicalHeightForBoxSizing()) : logicalHeight;
 }
 
 void LayoutView::updateLogicalWidth()
 {
@@ skipping 828 matching lines @@
     return viewHeight(IncludeScrollbars) / scale;
 }
 
 void LayoutView::willBeDestroyed()
 {
     LayoutBlockFlow::willBeDestroyed();
     m_compositor.clear();
 }
 
 } // namespace blink