Implement a Hit Test Cache.

Source/core/layout/LayoutView.cpp

Index: Source/core/layout/LayoutView.cpp
diff --git a/Source/core/layout/LayoutView.cpp b/Source/core/layout/LayoutView.cpp
index d5102965e0d2959f55fff0960a523db1cbae834d..e52cea29f08306741b988dde2f4adf11b78d09b4 100644
--- a/Source/core/layout/LayoutView.cpp
+++ b/Source/core/layout/LayoutView.cpp
@@ -28,7 +28,6 @@
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/html/HTMLIFrameElement.h"
 #include "core/layout/ColumnInfo.h"
-#include "core/layout/HitTestResult.h"
 #include "core/layout/LayoutFlowThread.h"
 #include "core/layout/LayoutGeometryMap.h"
 #include "core/layout/LayoutPart.h"
@@ -42,6 +41,7 @@
 #include "platform/TraceEvent.h"
 #include "platform/geometry/FloatQuad.h"
 #include "platform/geometry/TransformState.h"
+#include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/DisplayItemList.h"
 
 namespace blink {
@@ -59,6 +59,7 @@ LayoutView::LayoutView(Document* document)
     , m_layoutQuoteHead(nullptr)
     , m_layoutCounterCount(0)
     , m_hitTestCount(0)
+    , m_hitTestCacheHits(0)
     , m_pendingSelection(PendingSelection::create())
 {
     // init LayoutObject attributes
@@ -78,15 +79,10 @@ 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_EVENT0("blink", "LayoutView::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
@@ -96,18 +92,57 @@ bool LayoutView::hitTest(const HitTestRequest& request, const HitTestLocation& l
     frameView()->updateLayoutAndStyleForPainting();
     commitPendingSelection();
 
-    bool hitLayer = layer()->hitTest(request, location, result);
+    bool cacheHit = false;
+    // Determine if we should use the hit test cache.
+    if (frameView()->layoutCount() == m_hitTestCacheLayoutCount) {
+        if (!m_hitTestCacheResult.hitTestLocation().isRectBasedTest() && !result.hitTestLocation().isRectBasedTest() && m_hitTestCacheResult.validityRect().contains(result.hitTestLocation().point())) {
+            if (result.hitTestRequest().equalForCacheability(m_hitTestCacheResult.hitTestRequest())) {
+                m_hitTestCacheHits++;
+                cacheHit = true;
+            }
+        }
+    }
+    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);
 
+    if (cacheHit) {
+        if (!m_hitTestCacheResult.equalForCacheability(result)) {
+            for (int i = 0; i < 10; ++i) {
+                layer()->hitTest(result);
+            }
+
+            WTF_LOG_ERROR("Hit failure with %lf %lf cache %lf %lf", result.hitTestLocation().point().x().toDouble(), result.hitTestLocation().point().y().toDouble(), m_hitTestCacheResult.hitTestLocation().point().x().toDouble(), m_hitTestCacheResult.hitTestLocation().point().y().toDouble());
+
+            // DCHECK that the cache hit is the same as the actual result
+            ASSERT(false);
+        }
+    }
+    if (hitLayer) {
+        m_hitTestCacheResult = result;
+        m_hitTestCacheLayoutCount = frameView()->layoutCount();
+
+        // TODO(dtapuska): We shouldn't send the hit cache result to the compositor if
+        // we aren't displaying it in HUD: as it slows everything down.
+        if (layer()->graphicsLayerBacking()) {
+            layer()->graphicsLayerBacking()->platformLayer()->setHitCacheRect(enclosingIntRect(m_hitTestCacheResult.validityRect()));
+        }
+    }
+
     return hitLayer;
 }
 
+void LayoutView::clearHitTestCache()
+{
+    m_hitTestCacheResult = HitTestResult();
+    m_hitTestCacheLayoutCount = 0;
+}
+
 void LayoutView::computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit, LogicalExtentComputedValues& computedValues) const
 {
     computedValues.m_extent = (!shouldUsePrintingLayout() && m_frameView) ? LayoutUnit(viewLogicalHeight()) : logicalHeight;
@@ -883,11 +918,12 @@ float LayoutView::zoomFactor() const
     return m_frameView->frame().pageZoomFactor();
 }
 
-void LayoutView::updateHitTestResult(HitTestResult& result, const LayoutPoint& point)
+void LayoutView::updateHitTestResult(HitTestResult& result, const LayoutPoint& point, const LayoutRect& rect)
 {
     if (result.innerNode())
         return;
 
+    result.intersectValidityRect(rect);
     Node* node = document().documentElement();
     if (node) {
         LayoutPoint adjustedPoint = point;