third_party/blink/renderer/platform/fonts/shaping/glyph_bounds_accumulator.h

/*
 * Copyright (c) 2012 Google Inc. All rights reserved.
 * Copyright (C) 2013 BlackBerry Limited. All rights reserved.
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 * notice, this list of conditions and the following disclaimer.
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 * in the documentation and/or other materials provided with the
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 * this software without specific prior written permission.
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#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_FONTS_SHAPING_GLYPH_BOUNDS_ACCUMULATOR_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_FONTS_SHAPING_GLYPH_BOUNDS_ACCUMULATOR_H_

#include "third_party/blink/renderer/platform/fonts/shaping/shape_result_inline_headers.h"
#include "third_party/blink/renderer/platform/geometry/float_rect.h"

namespace blink {

// Helper class to accumulate glyph bounding box.
//
// Glyph positions and bounding boxes from HarfBuzz and fonts are in physical
// coordinate, while ShapeResult::glyph_bounding_box_ is in logical coordinate.
// To minimize the number of conversions, this class accumulates the bounding
// boxes in physical coordinate, and convert the accumulated box to logical.
struct GlyphBoundsAccumulator {
  // Construct an accumulator with the logical glyph origin.
  explicit GlyphBoundsAccumulator(float origin) : origin(origin) {}

  // The accumulated glyph bounding box in physical coordinate, until
  // ConvertVerticalRunToLogical().
  FloatRect bounds;
  // The current origin, in logical coordinate.
  float origin;

  // Unite a glyph bounding box to |bounds|.
  template <bool is_horizontal_run>
  void Unite(const HarfBuzzRunGlyphData& glyph_data,
             FloatRect bounds_for_glyph) {
    if (UNLIKELY(bounds_for_glyph.IsEmpty()))
      return;

    // Glyphs are drawn at |origin + offset|. Move glyph_bounds to that point.
    // All positions in hb_glyph_position_t are relative to the current point.
    // https://behdad.github.io/harfbuzz/harfbuzz-Buffers.html#hb-glyph-position-t-struct
    if (is_horizontal_run)
      bounds_for_glyph.SetX(bounds_for_glyph.X() + origin);
    else
      bounds_for_glyph.SetY(bounds_for_glyph.Y() + origin);
    bounds_for_glyph.Move(glyph_data.offset);

    bounds.Unite(bounds_for_glyph);
  }

  // Non-template version of |Unite()|, see above.
  void Unite(bool is_horizontal_run,
             const HarfBuzzRunGlyphData& glyph,
             FloatRect bounds_for_glyph) {
    is_horizontal_run ? Unite<true>(glyph, bounds_for_glyph)
                      : Unite<false>(glyph, bounds_for_glyph);
  }

  // Convert vertical run glyph bounding box to logical. Horizontal runs do not
  // need conversions because physical and logical are the same.
  void ConvertVerticalRunToLogical(const FontMetrics& font_metrics) {
    // Convert physical glyph_bounding_box to logical.
    bounds = bounds.TransposedRect();

    // The glyph bounding box of a vertical run uses ideographic baseline.
    // Adjust the box Y position because the bounding box of a ShapeResult uses
    // alphabetic baseline.
    // See diagrams of base lines at
    // https://drafts.csswg.org/css-writing-modes-3/#intro-baselines
    int baseline_adjust = font_metrics.Ascent(kIdeographicBaseline) -
                          font_metrics.Ascent(kAlphabeticBaseline);
    bounds.SetY(bounds.Y() + baseline_adjust);
  }
};

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_FONTS_SHAPING_GLYPH_BOUNDS_ACCUMULATOR_H_