FirstMeaningfulPaint UMA

third_party/WebKit/Source/core/paint/FirstMeaningfulPaintDetector.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/paint/FirstMeaningfulPaintDetector.h"
+
+#include "core/css/FontFaceSet.h"
+#include "core/fetch/ResourceFetcher.h"
+#include "core/paint/PaintTiming.h"
+
+namespace blink {
+
+namespace {
+
+// Web fonts that laid out more than this number of characters block First
+// Meaningful Paint.
+const int kBlankCharactersThreshold = 200;
+
+// FirstMeaningfulPaintDetector stops observing layouts and reports First
+// Meaningful Paint when this duration passed from last network activity.
+const double kSecondsWithoutNetworkActivityThreshold = 2.0;
+
+} // namespace
+
+FirstMeaningfulPaintDetector& FirstMeaningfulPaintDetector::from(Document& document)
+{
+    return PaintTiming::from(document).firstMeaningfulPaintDetector();
+}
+
+FirstMeaningfulPaintDetector::FirstMeaningfulPaintDetector(PaintTiming* paintTiming)
+    : m_paintTiming(paintTiming)
+    , m_networkStableTimer(this, &FirstMeaningfulPaintDetector::networkStableTimerFired)
+{
+}
+
+Document* FirstMeaningfulPaintDetector::document()
+{
+    return m_paintTiming->document();
+}
+
+// Computes "layout significance" (http://goo.gl/rytlPL) of a layout operation.
+// Significance of a layout is the number of layout objects newly added to the
+// layout tree, weighted by page height (before and after the layout).
+// A paint after the most significance layout during page load is reported as
+// First Meaningful Paint.
+void FirstMeaningfulPaintDetector::markNextPaintAsMeaningfulIfNeeded(
+    const LayoutObjectCounter& counter, int contentsHeightBeforeLayout,
+    int contentsHeightAfterLayout, int visibleHeight)
+{
+    if (m_state == Reported)
+        return;
+
+    unsigned delta = counter.count() - m_prevLayoutObjectCount;
+    m_prevLayoutObjectCount = counter.count();
+
+    if (visibleHeight == 0)
+        return;
+
+    double ratioBefore = std::max(1.0, static_cast<double>(contentsHeightBeforeLayout) / visibleHeight);
+    double ratioAfter = std::max(1.0, static_cast<double>(contentsHeightAfterLayout) / visibleHeight);
+    double significance = delta / ((ratioBefore + ratioAfter) / 2);
+
+    // If the page has many blank characters, the significance value is
+    // accumulated until the text become visible.
+    int approximateBlankCharacterCount = FontFaceSet::approximateBlankCharacterCount(*document());
+    if (approximateBlankCharacterCount > kBlankCharactersThreshold) {
+        m_accumulatedSignificanceWhileHavingBlankText += significance;
+    } else {
+        significance += m_accumulatedSignificanceWhileHavingBlankText;
+        m_accumulatedSignificanceWhileHavingBlankText = 0;
+        if (significance > m_maxSignificanceSoFar) {
+            m_state = NextPaintIsMeaningful;
+            m_maxSignificanceSoFar = significance;
+        }
+    }
+}
+
+void FirstMeaningfulPaintDetector::notifyPaint()
+{
+    if (m_state != NextPaintIsMeaningful)
+        return;
+
+    // Skip document background-only paints.
+    if (m_paintTiming->firstPaint() == 0.0)
+        return;
+
+    m_provisionalFirstMeaningfulPaint = monotonicallyIncreasingTime();
+    m_state = NextPaintIsNotMeaningful;
+}
+
+void FirstMeaningfulPaintDetector::checkNetworkStable()
+{
+    DCHECK(document());
+    if (m_state == Reported || document()->fetcher()->hasPendingRequest())
+        return;
+
+    m_networkStableTimer.startOneShot(kSecondsWithoutNetworkActivityThreshold, BLINK_FROM_HERE);
+}
+
+void FirstMeaningfulPaintDetector::networkStableTimerFired(TimerBase*)
+{
+    if (m_state == Reported || !document() || document()->fetcher()->hasPendingRequest())
+        return;
+
+    if (m_provisionalFirstMeaningfulPaint)
+        m_paintTiming->setFirstMeaningfulPaint(m_provisionalFirstMeaningfulPaint);
+    m_state = Reported;
+}
+
+DEFINE_TRACE(FirstMeaningfulPaintDetector)
+{
+    visitor->trace(m_paintTiming);
+}
+
+} // namespace blink