adding baseline options for super/sub scripting

ui/gfx/render_text_harfbuzz.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/render_text_harfbuzz.h"
 
 #include <limits>
 
 #include "base/i18n/bidi_line_iterator.h"
 #include "base/i18n/break_iterator.h"
@@ skipping 457 matching lines @@
 }
 
 TextRunHarfBuzz::TextRunHarfBuzz()
     : width(0.0f),
       preceding_run_widths(0.0f),
       is_rtl(false),
       level(0),
       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),
       underline(false) {}
 
 TextRunHarfBuzz::~TextRunHarfBuzz() {}
 
 void TextRunHarfBuzz::GetClusterAt(size_t pos,
                                    Range* chars,
                                    Range* glyphs) const {
@@ skipping 524 matching lines @@
                                    background_is_transparent());
       Range glyphs_range = run.CharRangeToGlyphRange(segment.char_range);
       scoped_ptr<SkPoint[]> positions(new SkPoint[glyphs_range.length()]);
       SkScalar offset_x =
           preceding_segment_widths - run.positions[glyphs_range.start()].x();
       for (size_t j = 0; j < glyphs_range.length(); ++j) {
         positions[j] = run.positions[(glyphs_range.is_reversed()) ?
                                      (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());
            it != colors().breaks().end() &&
                it->first < segment.char_range.end();
            ++it) {
         const Range intersection =
             colors().GetRange(it).Intersect(segment.char_range);
         const Range colored_glyphs = run.CharRangeToGlyphRange(intersection);
         // The range may be empty if a portion of a multi-character grapheme is
@@ skipping 88 matching lines @@
     internal::TextRunHarfBuzz* run = new internal::TextRunHarfBuzz;
     run->range = Range(0, text.length());
     run_list_out->add(run);
     run_list_out->InitIndexMap();
     return;
   }
 
   // Temporarily apply composition underlines and selection colors.
   ApplyCompositionAndSelectionStyles();
 
   // Build the list of runs from the script items and ranged styles. Use an

[msw, 2015/02/18 23:32:08]

nit: "Build the run list from the script items and ranges styles and baselines."

[dschuyler, 2015/02/19 00:29:14]

Done.

   // empty color BreakList to avoid breaking runs at color boundaries.
   BreakList<SkColor> empty_colors;
   empty_colors.SetMax(text.length());
-  internal::StyleIterator style(empty_colors, styles());
+  internal::StyleIterator style(empty_colors, baselines(), styles());
 
   for (size_t run_break = 0; run_break < text.length();) {
     internal::TextRunHarfBuzz* run = new internal::TextRunHarfBuzz;
     run->range.set_start(run_break);
     run->font_style = (style.style(BOLD) ? Font::BOLD : 0) |
                       (style.style(ITALIC) ? Font::ITALIC : 0);
+    run->baseline_type = style.baseline();
     run->strike = style.style(STRIKE);
     run->diagonal_strike = style.style(DIAGONAL_STRIKE);
     run->underline = style.style(UNDERLINE);
     int32 script_item_break = 0;
     bidi_iterator.GetLogicalRun(run_break, &script_item_break, &run->level);
     // Odd BiDi embedding levels correspond to RTL runs.
     run->is_rtl = (run->level % 2) == 1;
     // Find the length and script of this script run.
     script_item_break = ScriptInterval(text, run_break,
         script_item_break - run_break, &run->script) + run_break;
@@ skipping 48 matching lines @@
   for (auto* run : run_list->runs())
     ShapeRun(text, run);
   run_list->ComputePrecedingRunWidths();
 }
 
 void RenderTextHarfBuzz::ShapeRun(const base::string16& text,
                                   internal::TextRunHarfBuzz* run) {
   const Font& primary_font = font_list().GetPrimaryFont();
   const std::string primary_family = primary_font.GetFontName();
   run->font_size = primary_font.GetFontSize();
+  run->baseline_offset = 0;
+  if (run->baseline_type != NORMAL_BASELINE) {
+    // Calculate a slightly smaller font. The ratio here is somewhat arbitrary.
+    // Proportions from 5/9 to 5/7 all look pretty good.
+    const float ratio = 5.0f / 9.0f;
+    run->font_size = round(primary_font.GetFontSize() * ratio);

[msw, 2015/02/18 23:32:08]

nit: I don't think round is commonly used in the Chromium codebase...
Perhaps use std::ceil(foo + 0.5) here and for SUPERIOR below?

[dschuyler, 2015/02/19 00:29:15]

That gets a bit confusing/less readable because it needs to be floor if less
than zero and ceil if greater or equal to zero.  Also, with ceil, the 0.5 would
need to be subtracted (which is weird looking).  Would you consider std::round
as a replacement for round()?  That way it's using the C++ call (and I find it
easier to read that ceil).

[msw, 2015/02/19 02:50:57]

std::round only seems to be used in 4 places in the codebase. I'm not sure why
that isn't used more widely, but it makes me hesitant to recommend its use...
Maybe use gfx::ToRoundedInt from ui/gfx/geometry/safe_integer_conversions.h. I
wonder what other places use that naive code snippet and have bugs for not
handling negative numbers correctly... +CC pkasting for advice.

[Peter Kasting, 2015/02/19 07:27:46]

std::round is C++11, and since we can't yet use the C++11 standard library, it's
out.  round(), without the std:: qualifier, is also C++11 AFAICT, but was in C99
and thus likely has such broad compiler support that the couple dozen places in
the codebase that reference it "happen to work".  ToRoundedInt() is probably the
best answer, and is nicer than round() anyway in that it clamps to an int for
you.  

Incidentally, some places in our code round away from zero (the default behavior
of round() and friends) while some round toward positive infinity ("floor(x +
0.5)").  This distinction may look like a bug, but at least in the spots I've
tried to "fix" it in the past, it turned out we were doing what we were because
of explicit specs to that effect, e.g. I guess CSS rounding is specified as
always being toward positive infinity.  Dumb.

[dschuyler, 2015/02/25 02:23:05]

Done.

+    switch (run->baseline_type) {
+      case SUPERSCRIPT:
+        run->baseline_offset =
+            primary_font.GetCapHeight() - primary_font.GetHeight();
+        break;
+      case SUPERIOR:
+        run->baseline_offset = round(primary_font.GetCapHeight() * ratio) -
+            primary_font.GetCapHeight();
+        break;
+      case SUBSCRIPT:
+        run->baseline_offset =
+            primary_font.GetHeight() - primary_font.GetBaseline();
+        break;
+      case INFERIOR: // fall through

[msw, 2015/02/18 23:32:08]

nit: trailing period.

[dschuyler, 2015/02/19 00:29:14]

Done.

+      default:
+        break;
+    }
+  }
 
   std::string best_family;
   FontRenderParams best_render_params;
   size_t best_missing_glyphs = std::numeric_limits<size_t>::max();
 
   for (const Font& font : font_list().GetFonts()) {
     if (CompareFamily(text, font.GetFontName(), font.GetFontRenderParams(),
                       run, &best_family, &best_render_params,
                       &best_missing_glyphs))
       return;
@@ skipping 237 matching lines @@
   DCHECK(!update_layout_run_list_);
   DCHECK(!update_display_run_list_);
   return text_elided() ? display_run_list_.get() : &layout_run_list_;
 }
 
 const internal::TextRunList* RenderTextHarfBuzz::GetRunList() const {
   return const_cast<RenderTextHarfBuzz*>(this)->GetRunList();
 }
 
 }  // namespace gfx