Fix   fallback glyph lookup

Source/platform/fonts/Font.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (c) 2007, 2008, 2010 Google 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
@@ skipping 495 matching lines @@
     ASSERT(node->isSystemFallback());
 
     // System fallback is character-dependent. When we get here, we
     // know that the character in question isn't in the system fallback
     // font's glyph page. Try to lazily create it here.
 
     // FIXME: Unclear if this should normalizeSpaces above 0xFFFF.
     // Doing so changes fast/text/international/plane2-diffs.html
     UChar32 characterToRender = c;
     if (characterToRender <=  0xFFFF)
         characterToRender = Character::normalizeSpaces(characterToRender);

[kochi, 2015/08/26 12:02:59]

  is translated to U+00A0, but at this point it's converted back to 0x20.

After this line,
 c = 0xa0
 characterToRender = 0x20

 
     const FontData* fontData = fontDataAt(0);
     if (fontData) {
         const SimpleFontData* fontDataToSubstitute = fontData->fontDataForCharacter(characterToRender);
         RefPtr<SimpleFontData> characterFontData = FontCache::fontCache()->fallbackFontForCharacter(m_fontDescription, characterToRender, fontDataToSubstitute);
         if (characterFontData && variant != NormalVariant) {
             characterFontData = characterFontData->variantFontData(m_fontDescription, variant);
         }
         if (characterFontData) {
             // Got the fallback glyph and font.
             GlyphPage* fallbackPage = GlyphPageTreeNode::getRootChild(characterFontData.get(), pageNumber)->page();
-            GlyphData data = fallbackPage && fallbackPage->glyphForCharacter(c) ? fallbackPage->glyphDataForCharacter(c) : characterFontData->missingGlyphData();
+            GlyphData data = fallbackPage && fallbackPage->glyphForCharacter(characterToRender) ? fallbackPage->glyphDataForCharacter(characterToRender) : characterFontData->missingGlyphData();

[kochi, 2015/08/26 12:02:59]

On this line, fallbackPage->glyphForCharacter(0xa0) fails as the font does not
have the glyph for it, so it falls back to characterFontData->missingGlyphData()
path.

[kojii, 2015/08/26 13:45:09]

Yeah, this code path looks ok, so the caller should get missingGlyphData, which
is glyph == 0.

When Font returns glyph == 0, why Linux does not render the glyph while Android
renders it is still a mystery.

What are the CSS in the reproducing pages? Do they specify the font family,
'serif', or nothing?

[kochi, 2015/08/26 16:06:07]

I think on Linux fallbackPage->glyphForCharacter(c) succeeds, and
missingGlyphData() is never
called (of course, it depends on the fontconfig settings, though).

On Android (JA locale), fallbackPage also contains MotoyaLMaru and if it's given
0xa0, lookup
fails again (this is hypothesis, needs verification).

             // Cache it so we don't have to do system fallback again next time.
             if (variant == NormalVariant) {
-                page->setGlyphDataForCharacter(c, data.glyph, data.fontData);
+                page->setGlyphDataForCharacter(characterToRender, data.glyph, data.fontData);
                 data.fontData->setMaxGlyphPageTreeLevel(std::max(data.fontData->maxGlyphPageTreeLevel(), node->level()));
-                if (data.fontData->platformData().isVerticalAnyUpright() && !data.fontData->isTextOrientationFallback() && !Character::isCJKIdeographOrSymbol(c))
-                    return glyphDataForNonCJKCharacterWithGlyphOrientation(c, m_fontDescription.isVerticalUpright(c), data, pageNumber);
+                if (data.fontData->platformData().isVerticalAnyUpright() && !data.fontData->isTextOrientationFallback() && !Character::isCJKIdeographOrSymbol(characterToRender))
+                    return glyphDataForNonCJKCharacterWithGlyphOrientation(characterToRender, m_fontDescription.isVerticalUpright(characterToRender), data, pageNumber);
             }
             return data;
         }
     }
 
     // Even system fallback can fail; use the missing glyph in that case.
     // FIXME: It would be nicer to use the missing glyph from the last resort font instead.
     ASSERT(primaryFont());
     GlyphData data = primaryFont()->missingGlyphData();
     if (variant == NormalVariant) {
@@ skipping 275 matching lines @@
 {
     return m_fontFallbackList && m_fontFallbackList->loadingCustomFonts();
 }
 
 bool Font::isFallbackValid() const
 {
     return !m_fontFallbackList || m_fontFallbackList->isValid();
 }
 
 } // namespace blink