impeller::TextContents Class Reference

#include <text_contents.h>

Inheritance diagram for impeller::TextContents:

Public Member Functions
	TextContents ()
	~TextContents ()
void	SetTextFrame (const std::shared_ptr< TextFrame > &frame)
void	SetColor (Color color)
void	SetForceTextColor (bool value)
	Force the text color to apply to the rendered glyphs, even if those glyphs are bitmaps. More...
void	SetTextProperties (Color color, bool stroke, Scalar stroke_width, Cap stroke_cap, Join stroke_join, Scalar stroke_miter)
	Must be set after text frame. More...
Color	GetColor () const
bool	CanInheritOpacity (const Entity &entity) const override
	Whether or not this contents can accept the opacity peephole optimization. More...
void	SetInheritedOpacity (Scalar opacity) override
	Inherit the provided opacity. More...
void	SetOffset (Vector2 offset)
std::optional< Rect >	GetTextFrameBounds () const
std::optional< Rect >	GetCoverage (const Entity &entity) const override
	Get the area of the render pass that will be affected when this contents is rendered. More...
void	PopulateGlyphAtlas (const std::shared_ptr< LazyGlyphAtlas > &lazy_glyph_atlas, Scalar scale) override
	Add any text data to the specified lazy atlas. The scale parameter must be used again later when drawing the text. More...
void	SetScale (Scalar scale)
bool	Render (const ContentContext &renderer, const Entity &entity, RenderPass &pass) const override
Public Member Functions inherited from impeller::Contents
	Contents ()
virtual	~Contents ()
virtual void	PopulateGlyphAtlas (const std::shared_ptr< LazyGlyphAtlas > &lazy_glyph_atlas, Scalar scale)
	Add any text data to the specified lazy atlas. The scale parameter must be used again later when drawing the text. More...
virtual bool	Render (const ContentContext &renderer, const Entity &entity, RenderPass &pass) const =0
virtual std::optional< Rect >	GetCoverage (const Entity &entity) const =0
	Get the area of the render pass that will be affected when this contents is rendered. More...
void	SetCoverageHint (std::optional< Rect > coverage_hint)
	Hint that specifies the coverage area of this Contents that will actually be used during rendering. This is for optimization purposes only and can not be relied on as a clip. May optionally affect the result of GetCoverage(). More...
const std::optional< Rect > &	GetCoverageHint () const
virtual bool	IsOpaque () const
	Whether this Contents only emits opaque source colors from the fragment stage. This value does not account for any entity properties (e.g. the blend mode), clips/visibility culling, or inherited opacity. More...
virtual ClipCoverage	GetClipCoverage (const Entity &entity, const std::optional< Rect > &current_clip_coverage) const
	Given the current pass space bounding rectangle of the clip buffer, return the expected clip coverage after this draw call. This should only be implemented for contents that may write to the clip buffer. More...
virtual std::optional< Snapshot >	RenderToSnapshot (const ContentContext &renderer, const Entity &entity, std::optional< Rect > coverage_limit=std::nullopt, const std::optional< SamplerDescriptor > &sampler_descriptor=std::nullopt, bool msaa_enabled=true, int32_t mip_count=1, const std::string &label="Snapshot") const
	Render this contents to a snapshot, respecting the entity's transform, path, clip depth, and blend mode. The result texture size is always the size of GetCoverage(entity). More...
virtual bool	ShouldRender (const Entity &entity, const std::optional< Rect > clip_coverage) const
std::optional< Size >	GetColorSourceSize () const
	Return the color source's intrinsic size, if available. More...
void	SetColorSourceSize (Size size)
virtual bool	CanInheritOpacity (const Entity &entity) const
	Whether or not this contents can accept the opacity peephole optimization. More...
virtual void	SetInheritedOpacity (Scalar opacity)
	Inherit the provided opacity. More...
virtual std::optional< Color >	AsBackgroundColor (const Entity &entity, ISize target_size) const
	Returns a color if this Contents will flood the given target_size with a color. This output color is the "Source" color that will be used for the Entity's blend operation. More...
virtual const FilterContents *	AsFilter () const
	Cast to a filter. Returns nullptr if this Contents is not a filter. More...
virtual bool	ApplyColorFilter (const ColorFilterProc &color_filter_proc)
	If possible, applies a color filter to this contents inputs on the CPU. More...

Additional Inherited Members
Public Types inherited from impeller::Contents
using	ColorFilterProc = std::function< Color(Color)>
using	RenderProc = std::function< bool(const ContentContext &renderer, const Entity &entity, RenderPass &pass)>
using	CoverageProc = std::function< std::optional< Rect >(const Entity &entity)>
Static Public Member Functions inherited from impeller::Contents
static std::shared_ptr< Contents >	MakeAnonymous (RenderProc render_proc, CoverageProc coverage_proc)

Detailed Description

Definition at line 20 of file text_contents.h.

Constructor & Destructor Documentation

TextContents()

impeller::TextContents::TextContents ( )

default

~TextContents()

impeller::TextContents::~TextContents ( )

default

Member Function Documentation

CanInheritOpacity()

bool impeller::TextContents::CanInheritOpacity ( const Entity &  entity ) const

overridevirtual

Whether or not this contents can accept the opacity peephole optimization.

By default all contents return false. Contents are responsible for determining whether or not their own geometries intersect in a way that makes accepting opacity impossible. It is always safe to return false, especially if computing overlap would be computationally expensive.

Reimplemented from impeller::Contents.

Definition at line 40 of file text_contents.cc.

                                                               {
  // Computing whether or not opacity can be inherited requires determining if
  // any glyphs can overlap exactly. While this was previously implemented
  // via TextFrame::MaybeHasOverlapping, this code relied on scaling up text
  // bounds for a size specified at 1.0 DPR, which was not accurate at
  // higher or lower DPRs. Rather than re-implement the checks to compute exact
  // glyph bounds, for now this optimization has been disabled for Text.
  return false;
}

GetColor()

Color impeller::TextContents::GetColor

(

)

const

Definition at line 36 of file text_contents.cc.

                                   {
  return color_.WithAlpha(color_.alpha * inherited_opacity_);
}

GetCoverage()

std::optional< Rect > impeller::TextContents::GetCoverage ( const Entity &  entity ) const

overridevirtual

Get the area of the render pass that will be affected when this contents is rendered.

During rendering, coverage coordinates count pixels from the top left corner of the framebuffer.

Returns

The coverage rectangle. An std::nullopt result means that rendering this contents has no effect on the output color.

Implements impeller::Contents.

Definition at line 62 of file text_contents.cc.

                                                                      {
  return frame_->GetBounds().TransformBounds(entity.GetTransform());
}

GetTextFrameBounds()

std::optional< Rect > impeller::TextContents::GetTextFrameBounds

(

)

const

PopulateGlyphAtlas()

void impeller::TextContents::PopulateGlyphAtlas ( const std::shared_ptr< LazyGlyphAtlas > &  lazy_glyph_atlas, Scalar  scale  )

overridevirtual

Add any text data to the specified lazy atlas. The scale parameter must be used again later when drawing the text.

Reimplemented from impeller::Contents.

Definition at line 66 of file text_contents.cc.

                  {
  lazy_glyph_atlas->AddTextFrame(*frame_, scale, offset_, properties_);
  scale_ = scale;
}

Render()

bool impeller::TextContents::Render ( const ContentContext &  renderer, const Entity &  entity, RenderPass &  pass  ) const

overridevirtual

Implements impeller::Contents.

Definition at line 93 of file text_contents.cc.

                                                  {
  auto color = GetColor();
  if (color.IsTransparent()) {
    return true;
  }
 
  auto type = frame_->GetAtlasType();
  const std::shared_ptr<GlyphAtlas>& atlas =
      renderer.GetLazyGlyphAtlas()->CreateOrGetGlyphAtlas(
          *renderer.GetContext(), renderer.GetTransientsBuffer(), type);
 
  if (!atlas || !atlas->IsValid()) {
    VALIDATION_LOG << "Cannot render glyphs without prepared atlas.";
    return false;
  }
 
  // Information shared by all glyph draw calls.
  pass.SetCommandLabel("TextFrame");
  auto opts = OptionsFromPassAndEntity(pass, entity);
  opts.primitive_type = PrimitiveType::kTriangle;
  pass.SetPipeline(renderer.GetGlyphAtlasPipeline(opts));
 
  using VS = GlyphAtlasPipeline::VertexShader;
  using FS = GlyphAtlasPipeline::FragmentShader;
 
  // Common vertex uniforms for all glyphs.
  VS::FrameInfo frame_info;
  frame_info.mvp =
      Entity::GetShaderTransform(entity.GetShaderClipDepth(), pass, Matrix());
  ISize atlas_size = atlas->GetTexture()->GetSize();
  bool is_translation_scale = entity.GetTransform().IsTranslationScaleOnly();
  Matrix entity_transform = entity.GetTransform();
  Matrix basis_transform = entity_transform.Basis();
 
  VS::BindFrameInfo(pass,
                    renderer.GetTransientsBuffer().EmplaceUniform(frame_info));
 
  FS::FragInfo frag_info;
  frag_info.use_text_color = force_text_color_ ? 1.0 : 0.0;
  frag_info.text_color = ToVector(color.Premultiply());
  frag_info.is_color_glyph = type == GlyphAtlas::Type::kColorBitmap;
 
  FS::BindFragInfo(pass,
                   renderer.GetTransientsBuffer().EmplaceUniform(frag_info));
 
  SamplerDescriptor sampler_desc;
  if (is_translation_scale) {
    sampler_desc.min_filter = MinMagFilter::kNearest;
    sampler_desc.mag_filter = MinMagFilter::kNearest;
  } else {
    // Currently, we only propagate the scale of the transform to the atlas
    // renderer, so if the transform has more than just a translation, we turn
    // on linear sampling to prevent crunchiness caused by the pixel grid not
    // being perfectly aligned.
    // The downside is that this slightly over-blurs rotated/skewed text.
    sampler_desc.min_filter = MinMagFilter::kLinear;
    sampler_desc.mag_filter = MinMagFilter::kLinear;
  }
 
  // No mipmaps for glyph atlas (glyphs are generated at exact scales).
  sampler_desc.mip_filter = MipFilter::kBase;
 
  FS::BindGlyphAtlasSampler(
      pass,                 // command
      atlas->GetTexture(),  // texture
      renderer.GetContext()->GetSamplerLibrary()->GetSampler(
          sampler_desc)  // sampler
  );
 
  // Common vertex information for all glyphs.
  // All glyphs are given the same vertex information in the form of a
  // unit-sized quad. The size of the glyph is specified in per instance data
  // and the vertex shader uses this to size the glyph correctly. The
  // interpolated vertex information is also used in the fragment shader to
  // sample from the glyph atlas.
 
  constexpr std::array<Point, 6> unit_points = {Point{0, 0}, Point{1, 0},
                                                Point{0, 1}, Point{1, 0},
                                                Point{0, 1}, Point{1, 1}};
 
  auto& host_buffer = renderer.GetTransientsBuffer();
  size_t vertex_count = 0;
  for (const auto& run : frame_->GetRuns()) {
    vertex_count += run.GetGlyphPositions().size();
  }
  vertex_count *= 6;
 
  BufferView buffer_view = host_buffer.Emplace(
      vertex_count * sizeof(VS::PerVertexData), alignof(VS::PerVertexData),
      [&](uint8_t* contents) {
        VS::PerVertexData vtx;
        VS::PerVertexData* vtx_contents =
            reinterpret_cast<VS::PerVertexData*>(contents);
        size_t i = 0u;
        for (const TextRun& run : frame_->GetRuns()) {
          const Font& font = run.GetFont();
          Scalar rounded_scale = TextFrame::RoundScaledFontSize(
              scale_, font.GetMetrics().point_size);
          const FontGlyphAtlas* font_atlas =
              atlas->GetFontGlyphAtlas(font, rounded_scale);
          if (!font_atlas) {
            VALIDATION_LOG << "Could not find font in the atlas.";
            continue;
          }
 
          // Adjust glyph position based on the subpixel rounding
          // used by the font.
          Point subpixel_adjustment(0.5, 0.5);
          switch (font.GetAxisAlignment()) {
            case AxisAlignment::kNone:
              break;
            case AxisAlignment::kX:
              subpixel_adjustment.x = 0.125;
              break;
            case AxisAlignment::kY:
              subpixel_adjustment.y = 0.125;
              break;
            case AxisAlignment::kAll:
              subpixel_adjustment.x = 0.125;
              subpixel_adjustment.y = 0.125;
              break;
          }
 
          Point screen_offset = (entity_transform * Point(0, 0));
          for (const TextRun::GlyphPosition& glyph_position :
               run.GetGlyphPositions()) {
            // Note: uses unrounded scale for more accurate subpixel position.
            Point subpixel = TextFrame::ComputeSubpixelPosition(
                glyph_position, font.GetAxisAlignment(), offset_, scale_);
            std::optional<std::pair<Rect, Rect>> maybe_atlas_glyph_bounds =
                font_atlas->FindGlyphBounds(
                    SubpixelGlyph{glyph_position.glyph, subpixel, properties_});
            if (!maybe_atlas_glyph_bounds.has_value()) {
              VALIDATION_LOG << "Could not find glyph position in the atlas.";
              continue;
            }
            const Rect& atlas_glyph_bounds =
                maybe_atlas_glyph_bounds.value().first;
            Rect glyph_bounds = maybe_atlas_glyph_bounds.value().second;
            // For each glyph, we compute two rectangles. One for the vertex
            // positions and one for the texture coordinates (UVs). The atlas
            // glyph bounds are used to compute UVs in cases where the
            // destination and source sizes may differ due to clamping the sizes
            // of large glyphs.
            Point uv_origin =
                (atlas_glyph_bounds.GetLeftTop() - Point(0.5, 0.5)) /
                atlas_size;
            Point uv_size =
                (atlas_glyph_bounds.GetSize() + Point(1, 1)) / atlas_size;
 
            Point unrounded_glyph_position =
                (basis_transform * glyph_position.position) +
                glyph_bounds.GetLeftTop();
            Point screen_glyph_position =
                (screen_offset + unrounded_glyph_position + subpixel_adjustment)
                    .Floor();
 
            Size scaled_size = glyph_bounds.GetSize();
            for (const Point& point : unit_points) {
              Point position;
              if (is_translation_scale) {
                position = screen_glyph_position + (point * scaled_size);
              } else {
                Rect scaled_bounds = glyph_bounds.Scale(1.0 / rounded_scale);
                position = entity_transform * (glyph_position.position +
                                               scaled_bounds.GetLeftTop() +
                                               point * scaled_bounds.GetSize());
              }
              vtx.uv = uv_origin + (uv_size * point);
              vtx.position = position;
              vtx_contents[i++] = vtx;
            }
          }
        }
      });
 
  pass.SetVertexBuffer({
      .vertex_buffer = std::move(buffer_view),
      .index_buffer = {},
      .vertex_count = vertex_count,
      .index_type = IndexType::kNone,
  });
 
  return pass.Draw().ok();
}

SetColor()

void impeller::TextContents::SetColor

(

Color

color

)

Definition at line 32 of file text_contents.cc.

                                       {
  color_ = color;
}

SetForceTextColor()

void impeller::TextContents::SetForceTextColor

(

bool

value

)

Force the text color to apply to the rendered glyphs, even if those glyphs are bitmaps.

This is used to ensure that mask blurs work correctly on emoji.

Definition at line 58 of file text_contents.cc.

                                               {
  force_text_color_ = value;
}

SetInheritedOpacity()

void impeller::TextContents::SetInheritedOpacity ( Scalar  opacity )

overridevirtual

Inherit the provided opacity.

   Use of this method is invalid if CanAcceptOpacity returns false.

Reimplemented from impeller::Contents.

Definition at line 50 of file text_contents.cc.

                                                     {
  inherited_opacity_ = opacity;
}

SetOffset()

void impeller::TextContents::SetOffset

(

Vector2

offset

)

Definition at line 54 of file text_contents.cc.

                                           {
  offset_ = offset;
}

SetScale()

void impeller::TextContents::SetScale ( Scalar  scale )

inline

Definition at line 65 of file text_contents.h.

{ scale_ = scale; }

SetTextFrame()

void impeller::TextContents::SetTextFrame

(

const std::shared_ptr< TextFrame > &

frame

)

Definition at line 28 of file text_contents.cc.

                                                                     {
  frame_ = frame;
}

SetTextProperties()

void impeller::TextContents::SetTextProperties	(	Color	color,
		bool	stroke,
		Scalar	stroke_width,
		Cap	stroke_cap,
		Join	stroke_join,
		Scalar	stroke_miter
	)

Must be set after text frame.

Definition at line 73 of file text_contents.cc.

                                                          {
  if (frame_->HasColor()) {
    // Alpha is always applied when rendering, remove it here so
    // we do not double-apply the alpha.
    properties_.color = color.WithAlpha(1.0);
  }
  if (stroke) {
    properties_.stroke = true;
    properties_.stroke_width = stroke_width;
    properties_.stroke_cap = stroke_cap;
    properties_.stroke_join = stroke_join;
    properties_.stroke_miter = stroke_miter;
  }
}

---

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

• impeller/entity/contents/text_contents.h
• impeller/entity/contents/text_contents.cc