Some fixes to the fallback font code.

This CL applies several fixes to the fallback font code.
- PDFium uses -1 to indicate that no glyph index was found, but freetype uses
0. In CPDF_TrueTypeFont, an index of 0 indicates a freetype failure, which
means we should try to find the glyph from a fallback font.
- Improve the fallback glyph calculation by going from original font charcode
to unicode to fallback font charcode.
- Consider the m_ExtGID on Mac when deciding the fallback.

Bug: chromium:665467
Change-Id: I2be34983e0d768d9a598043f84edd2d70f033c86
Reviewed-on: https://pdfium-review.googlesource.com/4055
Commit-Queue: Nicolás Peña <npm@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

4 files changed, 22 insertions, 15 deletions

diff --git a/core/fpdfapi/font/cpdf_font.cpp b/core/fpdfapi/font/cpdf_font.cpp
index a6a661b328..b9be3aa868 100644
--- a/core/fpdfapi/font/cpdf_font.cpp
+++ b/core/fpdfapi/font/cpdf_font.cpp
@@ -457,9 +457,12 @@ int CPDF_Font::FallbackGlyphFromCharcode(int fallbackFont, uint32_t charcode) {
   if (!pdfium::IndexInBounds(m_FontFallbacks, fallbackFont))
     return -1;
 
+  CFX_WideString str = UnicodeFromCharCode(charcode);
+  uint32_t unicode = !str.IsEmpty() ? str.GetAt(0) : charcode;
   int glyph =
-      FXFT_Get_Char_Index(m_FontFallbacks[fallbackFont]->GetFace(), charcode);
-  if (glyph == 0 || glyph == 0xffff)
+      FXFT_Get_Char_Index(m_FontFallbacks[fallbackFont]->GetFace(), unicode);
+  if (glyph == 0)
     return -1;
+
   return glyph;
 }
diff --git a/core/fpdfapi/font/cpdf_simplefont.cpp b/core/fpdfapi/font/cpdf_simplefont.cpp
index a3597824bd..cb8f00a98a 100644
--- a/core/fpdfapi/font/cpdf_simplefont.cpp
+++ b/core/fpdfapi/font/cpdf_simplefont.cpp
@@ -29,8 +29,11 @@ int CPDF_SimpleFont::GlyphFromCharCode(uint32_t charcode, bool* pVertGlyph) {
   if (charcode > 0xff)
     return -1;
 
-  int index = m_GlyphIndex[(uint8_t)charcode];
-  return index != 0xffff ? index : -1;
+  int index = m_GlyphIndex[charcode];
+  if (index == 0xffff || (index == 0 && IsTrueTypeFont()))
+    return -1;
+
+  return index;
 }
 
 void CPDF_SimpleFont::LoadCharMetrics(int charcode) {
diff --git a/core/fpdfapi/font/cpdf_truetypefont.cpp b/core/fpdfapi/font/cpdf_truetypefont.cpp
index 54e565bfd1..d78a5e0eb2 100644
--- a/core/fpdfapi/font/cpdf_truetypefont.cpp
+++ b/core/fpdfapi/font/cpdf_truetypefont.cpp
@@ -73,13 +73,11 @@ void CPDF_TrueTypeFont::LoadGlyphMap() {
         return;
 
       int charcode = 0;
-      for (; charcode < nStartChar; charcode++) {
+      for (; charcode < nStartChar; charcode++)
         m_GlyphIndex[charcode] = 0;
-      }
       uint16_t nGlyph = charcode - nStartChar + 3;
-      for (; charcode < 256; charcode++, nGlyph++) {
+      for (; charcode < 256; charcode++, nGlyph++)
         m_GlyphIndex[charcode] = nGlyph;
-      }
       return;
     }
     bool bMSUnicode = FT_UseTTCharmap(m_Font.GetFace(), 3, 1);
@@ -108,9 +106,8 @@ void CPDF_TrueTypeFont::LoadGlyphMap() {
           uint16_t unicode = kPrefix[j] * 256 + charcode;
           m_GlyphIndex[charcode] =
               FXFT_Get_Char_Index(m_Font.GetFace(), unicode);
-          if (m_GlyphIndex[charcode]) {
+          if (m_GlyphIndex[charcode])
             break;
-          }
         }
       } else if (m_Encoding.m_Unicodes[charcode]) {
         if (bMSUnicode) {
diff --git a/core/fpdfapi/render/cpdf_charposlist.cpp b/core/fpdfapi/render/cpdf_charposlist.cpp
index 6d4540e163..d4c6b3b5f9 100644
--- a/core/fpdfapi/render/cpdf_charposlist.cpp
+++ b/core/fpdfapi/render/cpdf_charposlist.cpp
@@ -39,19 +39,23 @@ void CPDF_CharPosList::Load(const std::vector<uint32_t>& charCodes,
       charpos.m_bFontStyle = true;
 
     charpos.m_GlyphIndex = pFont->GlyphFromCharCode(CharCode, &bVert);
-    if (charpos.m_GlyphIndex != static_cast<uint32_t>(-1)) {
+    uint32_t GlyphID = charpos.m_GlyphIndex;
+#if _FXM_PLATFORM_ == _FXM_PLATFORM_APPLE_
+    charpos.m_ExtGID = pFont->GlyphFromCharCodeExt(CharCode);
+    GlyphID = charpos.m_ExtGID;
+#endif
+    if (GlyphID != static_cast<uint32_t>(-1)) {
       charpos.m_FallbackFontPosition = -1;
     } else {
       charpos.m_FallbackFontPosition =
           pFont->FallbackFontFromCharcode(CharCode);
       charpos.m_GlyphIndex = pFont->FallbackGlyphFromCharcode(
           charpos.m_FallbackFontPosition, CharCode);
-    }
-
-// TODO(npm): Figure out how this affects m_ExtGID
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_APPLE_
-    charpos.m_ExtGID = pFont->GlyphFromCharCodeExt(CharCode);
+      charpos.m_ExtGID = charpos.m_GlyphIndex;
 #endif
+    }
+
     if (!pFont->IsEmbedded() && !pFont->IsCIDFont())
       charpos.m_FontCharWidth = pFont->GetCharWidthF(CharCode);
     else