Merge HarfBuzz kerning support from Blink

ui/gfx/render_text_harfbuzz.cc

Index: ui/gfx/render_text_harfbuzz.cc
diff --git a/ui/gfx/render_text_harfbuzz.cc b/ui/gfx/render_text_harfbuzz.cc
index 10e7a1a5276931a44ad6e8ff6643d5a03bba9ed9..138b859f1e6298b8df76a7af601875b7a073e6b7 100644
--- a/ui/gfx/render_text_harfbuzz.cc
+++ b/ui/gfx/render_text_harfbuzz.cc
@@ -126,6 +126,56 @@ hb_bool_t GetGlyphHorizontalOrigin(hb_font_t* font,
   return true;
 }
 
+hb_position_t GetGlyphHorizontalKerning(hb_font_t*,

[msw, 2014/05/27 22:00:59]

nit: give names to even unused parameters (this and last void*).

[ckocagil, 2014/05/28 01:07:10]

Done.

+                                        void* data,
+                                        hb_codepoint_t left_glyph,
+                                        hb_codepoint_t right_glyph,
+                                        void*) {
+  FontData* font_data = reinterpret_cast<FontData*>(data);
+  if (font_data->paint_.isVerticalText()) {
+    // We don't support cross-stream kerning.
+    return 0;
+  }
+
+  SkTypeface* typeface = font_data->paint_.getTypeface();
+  const uint16_t glyphs[2] = { left_glyph, right_glyph };
+  int32_t kerningAdjustments[1] = { 0 };

[msw, 2014/05/27 22:00:59]

nit: |kerning_adjustments|

[ckocagil, 2014/05/28 01:07:10]

Done.

+
+  if (typeface->getKerningPairAdjustments(glyphs, 2, kerningAdjustments)) {
+    SkScalar upm = SkIntToScalar(typeface->getUnitsPerEm());
+    SkScalar size = font_data->paint_.getTextSize();
+    return SkiaScalarToHarfBuzzPosition(
+        SkScalarMulDiv(SkIntToScalar(kerningAdjustments[0]), size, upm));
+  }
+
+  return 0;
+}
+
+hb_position_t GetGlyphVerticalKerning(hb_font_t*,
+                                      void* data,
+                                      hb_codepoint_t top_glyph,
+                                      hb_codepoint_t bottom_glyph,
+                                      void*) {
+  FontData* font_data = reinterpret_cast<FontData*>(data);
+  if (!font_data->paint_.isVerticalText()) {

[msw, 2014/05/27 22:00:59]

This is the only logical difference from the function above. I understand that
parity with Blink is valuable, but perhaps we could have both of our functions
call a common helper? (Blink could do the same, but that's not in scope)

[ckocagil, 2014/05/28 01:07:10]

Done, added a common helper.

+    // We don't support cross-stream kerning.
+    return 0;
+  }
+
+  SkTypeface* typeface = font_data->paint_.getTypeface();
+  const uint16_t glyphs[2] = { top_glyph, bottom_glyph };
+  int32_t kerningAdjustments[1] = { 0 };

[msw, 2014/05/27 22:00:59]

ditto nit: |kerning_adjustments|

[ckocagil, 2014/05/28 01:07:10]

Done.

+
+  if (typeface->getKerningPairAdjustments(glyphs, 2, kerningAdjustments)) {
+    SkScalar upm = SkIntToScalar(typeface->getUnitsPerEm());
+    SkScalar size = font_data->paint_.getTextSize();
+    return SkiaScalarToHarfBuzzPosition(
+        SkScalarMulDiv(SkIntToScalar(kerningAdjustments[0]), size, upm));
+  }
+
+  return 0;
+}
+
 // Writes the |extents| of |glyph|.
 hb_bool_t GetGlyphExtents(hb_font_t* font,
                           void* data,
@@ -144,7 +194,6 @@ hb_font_funcs_t* GetFontFuncs() {
 
   // We don't set callback functions which we can't support.
   // HarfBuzz will use the fallback implementation if they aren't set.
-  // TODO(ckocagil): Merge Blink's kerning funcs.
   if (!font_funcs) {
     // The object created by |hb_font_funcs_create()| below lives indefinitely
     // and is intentionally leaked.
@@ -152,8 +201,12 @@ hb_font_funcs_t* GetFontFuncs() {
     hb_font_funcs_set_glyph_func(font_funcs, GetGlyph, 0, 0);
     hb_font_funcs_set_glyph_h_advance_func(
         font_funcs, GetGlyphHorizontalAdvance, 0, 0);
+    hb_font_funcs_set_glyph_h_kerning_func(
+        font_funcs, GetGlyphHorizontalKerning, 0, 0);
     hb_font_funcs_set_glyph_h_origin_func(
         font_funcs, GetGlyphHorizontalOrigin, 0, 0);
+    hb_font_funcs_set_glyph_v_kerning_func(
+        font_funcs, GetGlyphVerticalKerning, 0, 0);
     hb_font_funcs_set_glyph_extents_func(
         font_funcs, GetGlyphExtents, 0, 0);
     hb_font_funcs_make_immutable(font_funcs);