A texture containing the bitmap representation of glyphs in different fonts along with the ability to query the location of specific font glyphs within the texture. More...

#include <glyph_atlas.h>

Public Types
enum class	Type { kAlphaBitmap , kColorBitmap }
	Describes how the glyphs are represented in the texture. More...

Public Member Functions
	GlyphAtlas (Type type, size_t initial_generation)
	Create an empty glyph atlas.

	~GlyphAtlas ()

bool	IsValid () const

Type	GetType () const
	Describes how the glyphs are represented in the texture.

void	SetTexture (std::shared_ptr< Texture > texture)
	Set the texture for the glyph atlas.

const std::shared_ptr< Texture > &	GetTexture () const
	Get the texture for the glyph atlas.

void	AddTypefaceGlyphPositionAndBounds (const FontGlyphPair &pair, Rect position, Rect bounds)
	Record the location of a specific font-glyph pair within the atlas.

size_t	GetGlyphCount () const
	Get the number of unique font-glyph pairs in this atlas.

size_t	IterateGlyphs (const std::function< bool(const ScaledFont &scaled_font, const SubpixelGlyph &glyph, const Rect &rect)> &iterator) const
	Iterate of all the glyphs along with their locations in the atlas.

std::optional< FrameBounds >	FindFontGlyphBounds (const FontGlyphPair &pair) const
	Find the location of a specific font-glyph pair in the atlas.

FontGlyphAtlas *	GetOrCreateFontGlyphAtlas (const ScaledFont &scaled_font)
	Obtain an interface for querying the location of glyphs in the atlas for the given font and scale. This provides a more efficient way to look up a run of glyphs in the same font.

size_t	GetAtlasGeneration () const
	Retrieve the generation id for this glyph atlas.

void	SetAtlasGeneration (size_t value)
	Update the atlas generation.

Detailed Description

A texture containing the bitmap representation of glyphs in different fonts along with the ability to query the location of specific font glyphs within the texture.

Definition at line 37 of file glyph_atlas.h.

Member Enumeration Documentation

◆ Type

enum class impeller::GlyphAtlas::Type

strong

Describes how the glyphs are represented in the texture.

Enumerator

kAlphaBitmap

The glyphs are reprsented at their requested size using only an 8-bit color channel.

This might be backed by a grey or red single channel texture, depending on the backend capabilities.

kColorBitmap

The glyphs are reprsented at their requested size using N32 premul colors.

Definition at line 41 of file glyph_atlas.h.

                  {
    //--------------------------------------------------------------------------
    /// The glyphs are reprsented at their requested size using only an 8-bit
    /// color channel.
    ///
    /// This might be backed by a grey or red single channel texture, depending
    /// on the backend capabilities.
    kAlphaBitmap,
 
    //--------------------------------------------------------------------------
    /// The glyphs are reprsented at their requested size using N32 premul
    /// colors.
    ///
    kColorBitmap,
  };

Constructor & Destructor Documentation

◆ GlyphAtlas()

impeller::GlyphAtlas::GlyphAtlas	(	Type	type,
		size_t	initial_generation
	)

Create an empty glyph atlas.

Parameters

[in]	type	How the glyphs are represented in the texture.
[in]	initial_generation	the atlas generation.

Definition at line 49 of file glyph_atlas.cc.

50 : type_(type), generation_(initial_generation) {}

type

GLenum type

Definition blit_command_gles.cc:153

◆ ~GlyphAtlas()

impeller::GlyphAtlas::~GlyphAtlas ( )

default

Member Function Documentation

◆ AddTypefaceGlyphPositionAndBounds()

void impeller::GlyphAtlas::AddTypefaceGlyphPositionAndBounds	(	const FontGlyphPair &	pair,
		Rect	position,
		Rect	bounds
	)

Record the location of a specific font-glyph pair within the atlas.

Parameters

[in]	pair	The font-glyph pair
[in]	rect	The position in the atlas
[in]	bounds	The bounds of the glyph at scale

Definition at line 78 of file glyph_atlas.cc.

                                                                {
  FontAtlasMap::iterator it = font_atlas_map_.find(pair.scaled_font);
  FML_DCHECK(it != font_atlas_map_.end());
  it->second.positions_[pair.glyph] =
      FrameBounds{position, bounds, /*is_placeholder=*/false};
}

References FML_DCHECK, impeller::FontGlyphPair::glyph, and impeller::FontGlyphPair::scaled_font.

◆ FindFontGlyphBounds()

std::optional< FrameBounds > impeller::GlyphAtlas::FindFontGlyphBounds ( const FontGlyphPair & pair ) const

Find the location of a specific font-glyph pair in the atlas.

Parameters

[in] pair The font-glyph pair

Returns: The location of the font-glyph pair in the atlas. std::nullopt if the pair is not in the atlas.

Definition at line 87 of file glyph_atlas.cc.

                                     {
  const auto& found = font_atlas_map_.find(pair.scaled_font);
  if (found == font_atlas_map_.end()) {
    return std::nullopt;
  }
  return found->second.FindGlyphBounds(pair.glyph);
}

References impeller::FontGlyphPair::glyph, and impeller::FontGlyphPair::scaled_font.

Referenced by impeller::BulkUpdateAtlasBitmap(), and impeller::UpdateAtlasBitmap().

◆ GetAtlasGeneration()

size_t impeller::GlyphAtlas::GetAtlasGeneration ( ) const

Retrieve the generation id for this glyph atlas.

        The generation id is used to match with a TextFrame to
        determine if the frame is guaranteed to already be populated
        in the atlas.

Definition at line 70 of file glyph_atlas.cc.

                                            {
  return generation_;
}

◆ GetGlyphCount()

size_t impeller::GlyphAtlas::GetGlyphCount ( ) const

Get the number of unique font-glyph pairs in this atlas.

Returns: The glyph count.

Definition at line 103 of file glyph_atlas.cc.

                                       {
  return std::accumulate(font_atlas_map_.begin(), font_atlas_map_.end(), 0,
                         [](const int a, const auto& b) {
                           return a + b.second.positions_.size();
                         });
}

◆ GetOrCreateFontGlyphAtlas()

FontGlyphAtlas * impeller::GlyphAtlas::GetOrCreateFontGlyphAtlas ( const ScaledFont & scaled_font )

Obtain an interface for querying the location of glyphs in the atlas for the given font and scale. This provides a more efficient way to look up a run of glyphs in the same font.

Parameters

[in]	font	The font
[in]	scale	The scale

Returns: A pointer to a FontGlyphAtlas, or nullptr if the font and scale are not available in the atlas. The pointer is only valid for the lifetime of the GlyphAtlas.

Definition at line 96 of file glyph_atlas.cc.

                                   {
  auto [iter, inserted] =
      font_atlas_map_.try_emplace(scaled_font, FontGlyphAtlas());
  return &iter->second;
}

◆ GetTexture()

const std::shared_ptr< Texture > & impeller::GlyphAtlas::GetTexture ( ) const

Get the texture for the glyph atlas.

Returns: The texture.

Definition at line 62 of file glyph_atlas.cc.

                                                           {
  return texture_;
}

Referenced by impeller::BulkUpdateAtlasBitmap(), and impeller::UpdateAtlasBitmap().

◆ GetType()

GlyphAtlas::Type impeller::GlyphAtlas::GetType ( ) const

Describes how the glyphs are represented in the texture.

Definition at line 58 of file glyph_atlas.cc.

                                         {
  return type_;
}

Referenced by impeller::BulkUpdateAtlasBitmap(), impeller::GetImageInfo(), and impeller::UpdateAtlasBitmap().

◆ IsValid()

bool impeller::GlyphAtlas::IsValid ( ) const

Definition at line 54 of file glyph_atlas.cc.

                               {
  return !!texture_;
}

◆ IterateGlyphs()

size_t impeller::GlyphAtlas::IterateGlyphs ( const std::function< bool(const ScaledFont &scaled_font, const SubpixelGlyph &glyph, const Rect &rect)> & iterator ) const

Iterate of all the glyphs along with their locations in the atlas.

Parameters

[in] iterator The iterator. Return false from the iterator to stop iterating.

Returns: The number of glyphs iterated over.

Definition at line 110 of file glyph_atlas.cc.

                                                                 {
  if (!iterator) {
    return 0u;
  }
 
  size_t count = 0u;
  for (const auto& font_value : font_atlas_map_) {
    for (const auto& glyph_value : font_value.second.positions_) {
      count++;
      if (!iterator(font_value.first, glyph_value.first,
                    glyph_value.second.atlas_bounds)) {
        return count;
      }
    }
  }
  return count;
}

◆ SetAtlasGeneration()

void impeller::GlyphAtlas::SetAtlasGeneration ( size_t value )

Update the atlas generation.

Definition at line 74 of file glyph_atlas.cc.

                                                     {
  generation_ = generation;
}

◆ SetTexture()

void impeller::GlyphAtlas::SetTexture ( std::shared_ptr< Texture > texture )

Set the texture for the glyph atlas.

Parameters

[in] texture The texture

Definition at line 66 of file glyph_atlas.cc.

                                                          {
  texture_ = std::move(texture);
}

References texture.

The documentation for this class was generated from the following files:

impeller/typographer/glyph_atlas.h
impeller/typographer/glyph_atlas.cc

Public Types

Public Member Functions

Detailed Description

Member Enumeration Documentation

◆ Type

Constructor & Destructor Documentation

◆ GlyphAtlas()

◆ ~GlyphAtlas()

Member Function Documentation

◆ AddTypefaceGlyphPositionAndBounds()

◆ FindFontGlyphBounds()

◆ GetAtlasGeneration()

◆ GetGlyphCount()

◆ GetOrCreateFontGlyphAtlas()

◆ GetTexture()

◆ GetType()

◆ IsValid()

◆ IterateGlyphs()

◆ SetAtlasGeneration()

◆ SetTexture()