adding baseline options for super/sub scripting

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 e4469a6fdfa2500f117317a0b22e84bfac6deb4c..2a584a37ac6e413713eccad5d5e82112d7a82b39 100644
--- a/ui/gfx/render_text_harfbuzz.cc
+++ b/ui/gfx/render_text_harfbuzz.cc
@@ -473,6 +473,8 @@ TextRunHarfBuzz::TextRunHarfBuzz()
       script(USCRIPT_INVALID_CODE),
       glyph_count(static_cast<size_t>(-1)),
       font_size(0),
+      baseline_offset(0),
+      baseline_type(0),
       font_style(0),
       strike(false),
       diagonal_strike(false),
@@ -967,7 +969,7 @@ void RenderTextHarfBuzz::DrawVisualText(Canvas* canvas) {
                                      (glyphs_range.start() - j) :
                                      (glyphs_range.start() + j)];
         positions[j].offset(SkIntToScalar(origin.x()) + offset_x,
-                            SkIntToScalar(origin.y()));
+                            SkIntToScalar(origin.y() + run.baseline_offset));
       }
       for (BreakList<SkColor>::const_iterator it =
                colors().GetBreak(segment.char_range.start());
@@ -1083,6 +1085,18 @@ void RenderTextHarfBuzz::ItemizeText() {
     run->range.set_start(run_break);
     run->font_style = (style.style(BOLD) ? Font::BOLD : 0) |
                       (style.style(ITALIC) ? Font::ITALIC : 0);
+    if (style.style(SUPERSCRIPT)) {
+      run->baseline_type = SUPERSCRIPT;
+    }
+    if (style.style(SUPERIOR)) {
+      run->baseline_type = SUPERIOR;
+    }
+    if (style.style(INFERIOR)) {
+      run->baseline_type = INFERIOR;
+    }
+    if (style.style(SUBSCRIPT)) {
+      run->baseline_type = SUBSCRIPT;
+    }
     run->strike = style.style(STRIKE);
     run->diagonal_strike = style.style(DIAGONAL_STRIKE);
     run->underline = style.style(UNDERLINE);
@@ -1149,6 +1163,31 @@ void RenderTextHarfBuzz::ShapeRun(internal::TextRunHarfBuzz* run) {
   const Font& primary_font = font_list().GetPrimaryFont();
   const std::string primary_family = primary_font.GetFontName();
   run->font_size = primary_font.GetFontSize();
+  if (run->baseline_type) {
+    // Calculate a slightly smaller font.

[msw, 2015/02/17 23:32:06]

nit: remove the line break in the comment.

[dschuyler, 2015/02/18 01:37:27]

Done.

+    // The ratio here is somewhat arbitrary.  Proportions from 5/9 to 5/7 all
+    // look pretty good.  Feel free to change this if someone on the UX team

[msw, 2015/02/17 23:32:06]

nit: omit the "Feel free" sentence.

[dschuyler, 2015/02/18 01:37:27]

Done.

+    // feels that the smaller script should be slightly different.
+    const float ratio = 5.0f / 9.0f;
+    run->font_size = round(primary_font.GetFontSize() * ratio);
+    int cap_height = round(primary_font.GetCapHeight() * ratio);
+    switch (run->baseline_type) {
+      case SUPERSCRIPT:
+        run->baseline_offset =
+            primary_font.GetCapHeight() - primary_font.GetHeight();
+        break;
+      case SUPERIOR:
+        run->baseline_offset = cap_height - primary_font.GetCapHeight();
+        break;
+      case INFERIOR:
+        run->baseline_offset = 0;
+        break;
+      case SUBSCRIPT:
+        run->baseline_offset =
+            primary_font.GetHeight() - primary_font.GetBaseline();
+        break;
+    }
+  }
 
   std::string best_family;
   FontRenderParams best_render_params;