Add cmap 3,0 (symbol) as Unicode fallback.

FreeType automatically selects the 'most Unicode' cmap available,
otherwise the default cmap is NULL. When this happens the fallback
should include the 3,0 symbol cmap, as is outlined in the Apple
TrueType documentation. This cmap should effectively be a Unicode
mapping, but exclusively in the private use area.

BUG=skia:1873,chromium:489452

Review URL: https://codereview.chromium.org/1163833003

3 files changed, 36 insertions, 45 deletions

diff --git a/resources/fonts/SpiderSymbol.ttf b/resources/fonts/SpiderSymbol.ttf
new file mode 100644
index 0000000000..ed651eaded
--- /dev/null
+++ b/resources/fonts/SpiderSymbol.ttf
diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index a4305bfa87..b3a65e1985 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -352,6 +352,16 @@ static SkFaceRec* ref_ft_face(const SkTypeface* typeface) {
 
     ft_face_setup_axes(rec->fFace, *data);
 
+    // FreeType will set the charmap to the "most unicode" cmap if it exists.
+    // If there are no unicode cmaps, the charmap is set to NULL.
+    // However, "symbol" cmaps should also be considered "fallback unicode" cmaps
+    // because they are effectively private use area only (even if they aren't).
+    // This is the last on the fallback list at
+    // https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6cmap.html
+    if (!rec->fFace->charmap) {
+        FT_Select_Charmap(rec->fFace, FT_ENCODING_MS_SYMBOL);
+    }
+
     rec->fNext = gFaceRecHead;
     gFaceRecHead = rec;
     return rec;
@@ -446,51 +456,14 @@ static bool getWidthAdvance(FT_Face face, int gId, int16_t* data) {
 }
 
 static void populate_glyph_to_unicode(FT_Face& face, SkTDArray<SkUnichar>* glyphToUnicode) {
-    // Check and see if we have Unicode cmaps.
-    for (int i = 0; i < face->num_charmaps; ++i) {
-        // CMaps known to support Unicode:
-        // Platform ID   Encoding ID   Name
-        // -----------   -----------   -----------------------------------
-        // 0             0,1           Apple Unicode
-        // 0             3             Apple Unicode 2.0 (preferred)
-        // 3             1             Microsoft Unicode UCS-2
-        // 3             10            Microsoft Unicode UCS-4 (preferred)
-        //
-        // See Apple TrueType Reference Manual
-        // http://developer.apple.com/fonts/TTRefMan/RM06/Chap6cmap.html
-        // http://developer.apple.com/fonts/TTRefMan/RM06/Chap6name.html#ID
-        // Microsoft OpenType Specification
-        // http://www.microsoft.com/typography/otspec/cmap.htm
-
-        FT_UShort platformId = face->charmaps[i]->platform_id;
-        FT_UShort encodingId = face->charmaps[i]->encoding_id;
-
-        if (platformId != 0 && platformId != 3) {
-            continue;
-        }
-        if (platformId == 3 && encodingId != 1 && encodingId != 10) {
-            continue;
-        }
-        bool preferredMap = ((platformId == 3 && encodingId == 10) ||
-                             (platformId == 0 && encodingId == 3));
-
-        FT_Set_Charmap(face, face->charmaps[i]);
-        if (glyphToUnicode->isEmpty()) {
-            glyphToUnicode->setCount(face->num_glyphs);
-            memset(glyphToUnicode->begin(), 0,
-                   sizeof(SkUnichar) * face->num_glyphs);
-        }
+    glyphToUnicode->setCount(face->num_glyphs);
+    sk_bzero(glyphToUnicode->begin(), sizeof((*glyphToUnicode)[0]) * face->num_glyphs);
 
-        // Iterate through each cmap entry.
-        FT_UInt glyphIndex;
-        for (SkUnichar charCode = FT_Get_First_Char(face, &glyphIndex);
-             glyphIndex != 0;
-             charCode = FT_Get_Next_Char(face, charCode, &glyphIndex)) {
-            if (charCode &&
-                    ((*glyphToUnicode)[glyphIndex] == 0 || preferredMap)) {
-                (*glyphToUnicode)[glyphIndex] = charCode;
-            }
-        }
+    FT_UInt glyphIndex;
+    SkUnichar charCode = FT_Get_First_Char(face, &glyphIndex);
+    while (glyphIndex) {
+        (*glyphToUnicode)[glyphIndex] = charCode;
+        charCode = FT_Get_Next_Char(face, charCode, &glyphIndex);
     }
 }
 
@@ -1507,7 +1480,8 @@ static EncodingProc find_encoding_proc(SkTypeface::Encoding enc) {
 }
 
 int SkTypeface_FreeType::onCharsToGlyphs(const void* chars, Encoding encoding,
-                                      uint16_t glyphs[], int glyphCount) const {
+                                         uint16_t glyphs[], int glyphCount) const
+{
     AutoFTAccess fta(this);
     FT_Face face = fta.face();
     if (!face) {
diff --git a/tests/FontHostTest.cpp b/tests/FontHostTest.cpp
index ff275e2ad5..db83e06b62 100644
--- a/tests/FontHostTest.cpp
+++ b/tests/FontHostTest.cpp
@@ -153,6 +153,22 @@ static void test_fontstream(skiatest::Reporter* reporter) {
     }
 }
 
+static void test_symbolfont(skiatest::Reporter* reporter) {
+    SkAutoTUnref<SkTypeface> typeface(GetResourceAsTypeface("/fonts/SpiderSymbol.ttf"));
+    if (!typeface) {
+        SkDebugf("Skipping FontHostTest::test_symbolfont\n");
+        return;
+    }
+
+    SkUnichar c = 0xf021;
+    uint16_t g;
+    SkPaint paint;
+    paint.setTypeface(typeface);
+    paint.setTextEncoding(SkPaint::kUTF32_TextEncoding);
+    paint.textToGlyphs(&c, 4, &g);
+    REPORTER_ASSERT(reporter, g == 3);
+}
+
 static void test_tables(skiatest::Reporter* reporter, SkTypeface* face) {
     if (false) { // avoid bit rot, suppress warning
         SkFontID fontID = face->uniqueID();
@@ -295,6 +311,7 @@ DEF_TEST(FontHost, reporter) {
     test_tables(reporter);
     test_fontstream(reporter);
     test_advances(reporter);
+    test_symbolfont(reporter);
 }
 
 // need tests for SkStrSearch