Canvas fillText and measureText handle ideographic spaces differently.

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 2047 matching lines @@
     //        between the EM box's top and bottom and the font's ascend and descend
     metrics->setEmHeightAscent(0);
     metrics->setEmHeightDescent(0);
 
     metrics->setHangingBaseline(-0.8f * ascent + baselineY);
     metrics->setAlphabeticBaseline(baselineY);
     metrics->setIdeographicBaseline(descent + baselineY);
     return metrics.release();
 }
 
+static inline bool isSpaceCharacters(UChar c)
+{
+    // According to specification all space characters should be replaced with 0x0020 space character.
+    // http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#text-preparation-algorithm
+    // The space characters according to specification are : U+0020, U+0009, U+000A, U+000C, and U+000D.
+    // http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#space-character
+    // This function returns true for 0x000B also, so that this is backward compatible.
+    // Otherwise, the test LayoutTests/canvas/philip/tests/2d.text.draw.space.collapse.space.html will fail
+    return c == 0x0009 || c == 0x000A || c == 0x000B || c == 0x000C || c == 0x000D;
+}
+
 static void replaceCharacterInString(String& text, WTF::CharacterMatchFunctionPtr matchFunction, const String& replacement)
 {
     const size_t replacementLength = replacement.length();
     size_t index = 0;
     while ((index = text.find(matchFunction, index)) != kNotFound) {
         text.replace(index, 1, replacement);
         index += replacementLength;
     }
 }
 
@@ skipping 26 matching lines @@
     gradient = c->fillGradient();
     if (fill && gradient && gradient->isZeroSize())
         return;
 
     FontCachePurgePreventer fontCachePurgePreventer;
 
     const Font& font = accessFont();
     const FontMetrics& fontMetrics = font.fontMetrics();
     // According to spec, all the space characters must be replaced with U+0020 SPACE characters.
     String normalizedText = text;
-    replaceCharacterInString(normalizedText, isSpaceOrNewline, " ");
+    replaceCharacterInString(normalizedText, isSpaceCharacters, " ");

[Justin Novosad, 2014/05/20 18:29:50]

What exactly is wrong with isSpaceOrNewline? Why are you defining a new function
instead of correcting isSpaceOrNewline?

 
     // FIXME: Need to turn off font smoothing.
 
     RenderStyle* computedStyle = canvas()->computedStyle();
     TextDirection direction = computedStyle ? computedStyle->direction() : LTR;
     bool isRTL = direction == RTL;
     bool override = computedStyle ? isOverride(computedStyle->unicodeBidi()) : false;
 
     TextRun textRun(normalizedText, 0, 0, TextRun::AllowTrailingExpansion, direction, override, true, TextRun::NoRounding);
     // Draw the item text at the correct point.
@@ skipping 245 matching lines @@
     c->setAlphaAsFloat(1.0);
     c->clearShadow();
     c->setCompositeOperation(CompositeSourceOver, blink::WebBlendModeNormal);
     c->drawFocusRing(path, focusRingWidth, focusRingOutline, focusRingColor);
     c->restore();
 
     didDraw(dirtyRect);
 }
 
 } // namespace WebCore