Speed-up font switching in CanvasRenderingContext2D by only validating uncached values

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 61 matching lines @@
 #include "wtf/MathExtras.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/text/StringBuilder.h"
 
 namespace blink {
 
 static const int defaultFontSize = 10;
 static const char defaultFontFamily[] = "sans-serif";
 static const char defaultFont[] = "10px sans-serif";
 static const char inherit[] = "inherit";
+static const char initial[] = "initial";
 static const char rtl[] = "rtl";
 static const char ltr[] = "ltr";
 static const double TryRestoreContextInterval = 0.5;
 static const unsigned MaxTryRestoreContextAttempts = 4;
 static const unsigned FetchedFontsCacheLimit = 50;
 static const float cDeviceScaleFactor = 1.0f; // Canvas is device independent
 
 static bool contextLostRestoredEventsEnabled()
 {
     return RuntimeEnabledFeatures::experimentalCanvasFeaturesEnabled();
@@ skipping 1580 matching lines @@
     if (i != m_fetchedFonts.end()) {
         parsedStyle = i->value;
         m_fetchedFontsLRUList.remove(newFont);
     } else {
         parsedStyle = MutableStylePropertySet::create();
         CSSParser::parseValue(parsedStyle.get(), CSSPropertyFont, newFont, true, HTMLStandardMode, 0);
         if (m_fetchedFonts.size() >= FetchedFontsCacheLimit) {
             m_fetchedFonts.remove(m_fetchedFontsLRUList.first());
             m_fetchedFontsLRUList.removeFirst();
         }
+        if (parsedStyle->isEmpty())
+            return;
+        String fontValue = parsedStyle->getPropertyValue(CSSPropertyFont);
+        // According to http://lists.w3.org/Archives/Public/public-html/2009Jul/0947.html,
+        // the "inherit" and "initial" values must be ignored.
+        if (fontValue == inherit || fontValue == initial)
+            return;
         m_fetchedFonts.add(newFont, parsedStyle);
     }
     m_fetchedFontsLRUList.add(newFont);
 
-    if (parsedStyle->isEmpty())
-        return;
-
-    String fontValue = parsedStyle->getPropertyValue(CSSPropertyFont);
-
-    // According to http://lists.w3.org/Archives/Public/public-html/2009Jul/0947.html,
-    // the "inherit" and "initial" values must be ignored.
-    if (fontValue == "inherit" || fontValue == "initial")
-        return;
-
     // The parse succeeded.
     String newFontSafeCopy(newFont); // Create a string copy since newFont can be deleted inside realizeSaves.
     modifiableState().setUnparsedFont(newFontSafeCopy);
 
     // Map the <canvas> font into the text style. If the font uses keywords like larger/smaller, these will work
     // relative to the canvas.
     RefPtr<ComputedStyle> newStyle = ComputedStyle::create();
     canvas()->document().updateLayoutTreeIfNeeded();
     if (const ComputedStyle* computedStyle = canvas()->ensureComputedStyle()) {
         FontDescription elementFontDescription(computedStyle->fontDescription());
@@ skipping 531 matching lines @@
         if (imageType == CanvasRenderingContext2DState::NonOpaqueImage)
             return;
         if (alpha < 0xFF)
             return;
     }
 
     canvas()->buffer()->willOverwriteCanvas();
 }
 
 } // namespace blink