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* Copyright 2014 Google Inc. All Rights Reserved.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <vector>
#include "base/memory/ref_counted.h"
#include "cobalt/math/rect_f.h"
#include "cobalt/render_tree/glyph.h"
#include "cobalt/render_tree/typeface.h"
namespace cobalt {
namespace render_tree {
// Contains metrics common to all glyphs in the font.
class FontMetrics {
FontMetrics(float ascent, float descent, float leading, float x_height)
: ascent_(ascent),
x_height_(x_height) {}
float ascent() const { return ascent_; }
float descent() const { return descent_; }
float leading() const { return leading_; }
float x_height() const { return x_height_; }
float em_box_height() const { return ascent_ + descent_ + leading_; }
float baseline_offset_from_top() const { return ascent_ + leading_ / 2; }
// The recommended distance above the baseline.
float ascent_;
// The recommended distance below the baseline.
float descent_;
// The recommended distance to add between lines of text.
float leading_;
// The x-height, aka the height of the 'x' glyph, used for centering.
// See also
float x_height_;
// Used as a parameter to GetLocalTypeface() and GetCharacterFallbackTypeface()
// to describe the font style the caller is seeking.
struct FontStyle {
enum Weight {
kThinWeight = 100,
kExtraLightWeight = 200,
kLightWeight = 300,
kNormalWeight = 400,
kMediumWeight = 500,
kSemiBoldWeight = 600,
kBoldWeight = 700,
kExtraBoldWeight = 800,
kBlackWeight = 900
enum Slant {
FontStyle() : weight(kNormalWeight), slant(kUprightSlant) {}
FontStyle(Weight font_weight, Slant font_slant)
: weight(font_weight), slant(font_slant) {}
Weight weight;
Slant slant;
// The Font class is an abstract base class representing a typeface with a
// specific size. It provides the font metrics common to all glyphs in the
// font, and supports retrieval of both the glyph that it uses for each UTF-32
// character and the bounds and width information for any of its contained
// glyphs. Since Font objects may be created in the front-end, but must be
// accessed by the rasterizer during GlyphBuffer creation, it is expected that
// they will be downcast again to a rasterizer-specific type through
// base::polymorphic_downcast().
// NOTE: Font objects are not immutable and offer no thread safety guarantees.
// While Font is intended to assist in the creation of GlyphBuffer objects, only
// GlyphBuffer objects, which are immutable and thread-safe, should be accessed
// on multiple threads.
class Font : public base::RefCounted<Font> {
// Returns the font's typeface id, which is guaranteed to be unique among the
// typefaces registered with the font's resource provider.
virtual TypefaceId GetTypefaceId() const = 0;
// Returns the metrics common to all glyphs in the font. Used to calculate
// the recommended line height and spacing between the lines.
virtual FontMetrics GetFontMetrics() const = 0;
// Returns an index to the glyph that the font provides for a given UTF-32
// unicode character. If the character is unsupported, then it returns
// kInvalidGlyphIndex.
virtual GlyphIndex GetGlyphForCharacter(int32 utf32_character) = 0;
// Returns the bounding box for a given glyph. While left is always zero,
// note that since the glyph is output with the origin vertically on the
// baseline, the top of the bounding box will likely be non-zero and is used
// to indicate the offset of the glyph bounding box from the origin. The
// return value is given in units of pixels.
virtual const math::RectF& GetGlyphBounds(GlyphIndex glyph) = 0;
// Returns the width of a given glyph. The return value is given in units of
// pixels.
virtual float GetGlyphWidth(GlyphIndex glyph) = 0;
virtual ~Font() {}
// Allow the reference counting system access to our destructor.
friend class base::RefCounted<Font>;
typedef std::vector<scoped_refptr<Font> > FontVector;
} // namespace render_tree
} // namespace cobalt