impeller::GaussianBlurFilterContents Class Reference

#include <gaussian_blur_filter_contents.h>

Inheritance diagram for impeller::GaussianBlurFilterContents:

Public Member Functions
	GaussianBlurFilterContents (Scalar sigma_x, Scalar sigma_y, Entity::TileMode tile_mode, BlurStyle mask_blur_style, const Geometry *mask_geometry=nullptr)
Scalar	GetSigmaX () const
Scalar	GetSigmaY () const
std::optional< Rect >	GetFilterSourceCoverage (const Matrix &effect_transform, const Rect &output_limit) const override
	Internal utility method for |GetSourceCoverage| that computes the inverse effect of this transform on the specified output coverage, ignoring the inputs which will be accommodated by the caller.
std::optional< Rect >	GetFilterCoverage (const FilterInput::Vector &inputs, const Entity &entity, const Matrix &effect_transform) const override
	Internal utility method for |GetLocalCoverage| that computes the output coverage of this filter across the specified inputs, ignoring the coverage hint.
Public Member Functions inherited from impeller::FilterContents
	FilterContents ()
	~FilterContents () override
void	SetInputs (FilterInput::Vector inputs)
	The input texture sources for this filter. Each input's emitted texture is expected to have premultiplied alpha colors.
void	SetEffectTransform (const Matrix &effect_transform)
	Sets the transform which gets appended to the effect of this filter. Note that this is in addition to the entity's transform.
std::optional< Entity >	GetEntity (const ContentContext &renderer, const Entity &entity, const std::optional< Rect > &coverage_hint) const
	Create an Entity that renders this filter's output.
bool	Render (const ContentContext &renderer, const Entity &entity, RenderPass &pass) const override
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.
std::optional< Snapshot >	RenderToSnapshot (const ContentContext &renderer, const Entity &entity, const SnapshotOptions &options) const override
	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).
std::optional< Rect >	GetSourceCoverage (const Matrix &effect_transform, const Rect &output_limit) const
	Determines the coverage of source pixels that will be needed to produce results for the specified |output_limit| under the specified |effect_transform|. This is essentially a reverse of the |GetCoverage| method computing a source coverage from an intended |output_limit| coverage.
virtual Matrix	GetLocalTransform (const Matrix &parent_transform) const
Matrix	GetTransform (const Matrix &parent_transform) const
virtual void	SetRenderingMode (Entity::RenderingMode rendering_mode)
	Marks this filter chain as applying in a subpass scenario.
Public Member Functions inherited from impeller::Contents
	Contents ()
virtual	~Contents ()
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().
const std::optional< Rect > &	GetCoverageHint () const
virtual bool	IsOpaque (const Matrix &transform) 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.
std::optional< Size >	GetColorSourceSize () const
	Return the color source's intrinsic size, if available.
void	SetColorSourceSize (Size size)
virtual void	SetInheritedOpacity (Scalar opacity)
	Inherit the provided opacity.
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.
virtual bool	ApplyColorFilter (const ColorFilterProc &color_filter_proc)
	If possible, applies a color filter to this contents inputs on the CPU.

Static Public Member Functions
static Scalar	CalculateBlurRadius (Scalar sigma)
static Quad	CalculateUVs (const std::shared_ptr< FilterInput > &filter_input, const Entity &entity, const Rect &source_rect, const ISize &texture_size)
static Scalar	CalculateScale (Scalar sigma)
static Scalar	ScaleSigma (Scalar sigma)
Static Public Member Functions inherited from impeller::FilterContents
static std::shared_ptr< FilterContents >	MakeGaussianBlur (const FilterInput::Ref &input, Sigma sigma_x, Sigma sigma_y, Entity::TileMode tile_mode=Entity::TileMode::kDecal, BlurStyle mask_blur_style=BlurStyle::kNormal, const Geometry *mask_geometry=nullptr)
static std::shared_ptr< FilterContents >	MakeBorderMaskBlur (FilterInput::Ref input, Sigma sigma_x, Sigma sigma_y, BlurStyle blur_style=BlurStyle::kNormal)
static std::shared_ptr< FilterContents >	MakeDirectionalMorphology (FilterInput::Ref input, Radius radius, Vector2 direction, MorphType morph_type)
static std::shared_ptr< FilterContents >	MakeMorphology (FilterInput::Ref input, Radius radius_x, Radius radius_y, MorphType morph_type)
static std::shared_ptr< FilterContents >	MakeMatrixFilter (FilterInput::Ref input, const Matrix &matrix, const SamplerDescriptor &desc)
static std::shared_ptr< FilterContents >	MakeLocalMatrixFilter (FilterInput::Ref input, const Matrix &matrix)
static std::shared_ptr< FilterContents >	MakeYUVToRGBFilter (std::shared_ptr< Texture > y_texture, std::shared_ptr< Texture > uv_texture, YUVColorSpace yuv_color_space)
static std::shared_ptr< FilterContents >	MakeRuntimeEffect (FilterInput::Ref input, std::shared_ptr< RuntimeStage > runtime_stage, std::shared_ptr< std::vector< uint8_t > > uniforms, std::vector< RuntimeEffectContents::TextureInput > texture_inputs)
Static Public Member Functions inherited from impeller::Contents
static std::shared_ptr< Contents >	MakeAnonymous (RenderProc render_proc, CoverageProc coverage_proc)

Additional Inherited Members
Public Types inherited from impeller::FilterContents
enum class	BlurStyle {   kNormal ,   kSolid ,   kOuter ,   kInner }
enum class	MorphType {   kDilate ,   kErode }
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 Attributes inherited from impeller::FilterContents
static const int32_t	kBlurFilterRequiredMipCount

Detailed Description

Performs a bidirectional Gaussian blur.

This is accomplished by rendering multiple passes in multiple directions. Note: This will replace DirectionalGaussianBlurFilterContents.

Definition at line 56 of file gaussian_blur_filter_contents.h.

Constructor & Destructor Documentation

GaussianBlurFilterContents()

impeller::GaussianBlurFilterContents::GaussianBlurFilterContents ( Scalar  sigma_x, Scalar  sigma_y, Entity::TileMode  tile_mode, BlurStyle  mask_blur_style, const Geometry *  mask_geometry = nullptr  )

explicit

Definition at line 631 of file gaussian_blur_filter_contents.cc.

    : sigma_(sigma_x, sigma_y),
      tile_mode_(tile_mode),
      mask_blur_style_(mask_blur_style),
      mask_geometry_(mask_geometry) {
  // This is supposed to be enforced at a higher level.
  FML_DCHECK(mask_blur_style == BlurStyle::kNormal || mask_geometry);
}

References FML_DCHECK, and impeller::FilterContents::kNormal.

Member Function Documentation

CalculateBlurRadius()

Scalar impeller::GaussianBlurFilterContents::CalculateBlurRadius ( Scalar  sigma )

static

Given a sigma (standard deviation) calculate the blur radius (1/2 the kernel size).

Definition at line 882 of file gaussian_blur_filter_contents.cc.

                                                                   {
  return static_cast<Radius>(Sigma(sigma)).radius;
}

Referenced by CalculateScale(), GetFilterSourceCoverage(), impeller::testing::TEST(), impeller::testing::TEST(), and impeller::testing::TEST().

CalculateScale()

Scalar impeller::GaussianBlurFilterContents::CalculateScale ( Scalar  sigma )

static

Calculate the scale factor for the downsample pass given a sigma value.

Visible for testing.

Definition at line 648 of file gaussian_blur_filter_contents.cc.

                                                              {
  if (sigma <= 4) {
    return 1.0;
  }
  Scalar raw_result = 4.0 / sigma;
  // Round to the nearest 1/(2^n) to get the best quality down scaling.
  Scalar exponent = round(log2f(raw_result));
  // Don't scale down below 1/16th to preserve signal.
  exponent = std::max(-4.0f, exponent);
  Scalar rounded = powf(2.0f, exponent);
  Scalar result = rounded;
  // Extend the range of the 1/8th downsample based on the effective kernel size
  // for the blur.
  if (rounded < 0.125f) {
    Scalar rounded_plus = powf(2.0f, exponent + 1);
    Scalar blur_radius = CalculateBlurRadius(sigma);
    int kernel_size_plus = (ScaleBlurRadius(blur_radius, rounded_plus) * 2) + 1;
    // This constant was picked by looking at the results to make sure no
    // shimmering was introduced at the highest sigma values that downscale to
    // 1/16th.
    static constexpr int32_t kEighthDownsampleKernalWidthMax = 41;
    result = kernel_size_plus <= kEighthDownsampleKernalWidthMax ? rounded_plus
                                                                 : rounded;
  }
  return result;
};

References blur_radius, and CalculateBlurRadius().

Referenced by impeller::testing::TEST().

CalculateUVs()

Quad impeller::GaussianBlurFilterContents::CalculateUVs ( const std::shared_ptr< FilterInput > &  filter_input, const Entity &  entity, const Rect &  source_rect, const ISize &  texture_size  )

static

Calculate the UV coordinates for rendering the filter_input.

Parameters

filter_input	The FilterInput that should be rendered.
entity	The associated entity for the filter_input.
source_rect	The rect in source coordinates to convert to uvs.
texture_size	The rect to convert in source coordinates.

Definition at line 886 of file gaussian_blur_filter_contents.cc.

                               {
  Matrix input_transform = filter_input->GetLocalTransform(entity);
  Quad coverage_quad = source_rect.GetTransformedPoints(input_transform);
 
  Matrix uv_transform = Matrix::MakeScale(
      {1.0f / texture_size.width, 1.0f / texture_size.height, 1.0f});
  return uv_transform.Transform(coverage_quad);
}

References impeller::TRect< T >::GetTransformedPoints(), impeller::TSize< T >::height, impeller::Matrix::MakeScale(), impeller::Matrix::Transform(), and impeller::TSize< T >::width.

Referenced by impeller::testing::TEST_P().

GetFilterCoverage()

std::optional< Rect > impeller::GaussianBlurFilterContents::GetFilterCoverage ( const FilterInput::Vector &  inputs, const Entity &  entity, const Matrix &  effect_transform  ) const

overridevirtual

Internal utility method for |GetLocalCoverage| that computes the output coverage of this filter across the specified inputs, ignoring the coverage hint.

Reimplemented from impeller::FilterContents.

Definition at line 686 of file gaussian_blur_filter_contents.cc.

                                          {
  if (inputs.empty()) {
    return {};
  }
  std::optional<Rect> input_coverage = inputs[0]->GetCoverage(entity);
  if (!input_coverage.has_value()) {
    return {};
  }
 
  BlurInfo blur_info = CalculateBlurInfo(entity, effect_transform, sigma_);
  return input_coverage.value().Expand(
      Point(blur_info.local_padding.x, blur_info.local_padding.y));
}

Referenced by impeller::testing::TEST(), impeller::testing::TEST(), impeller::testing::TEST(), impeller::testing::TEST_P(), and impeller::testing::TEST_P().

GetFilterSourceCoverage()

std::optional< Rect > impeller::GaussianBlurFilterContents::GetFilterSourceCoverage ( const Matrix &  effect_transform, const Rect &  output_limit  ) const

overridevirtual

Internal utility method for |GetSourceCoverage| that computes the inverse effect of this transform on the specified output coverage, ignoring the inputs which will be accommodated by the caller.

Implements impeller::FilterContents.

Definition at line 675 of file gaussian_blur_filter_contents.cc.

                                    {
  Vector2 scaled_sigma = {ScaleSigma(sigma_.x), ScaleSigma(sigma_.y)};
  Vector2 blur_radius = {CalculateBlurRadius(scaled_sigma.x),
                         CalculateBlurRadius(scaled_sigma.y)};
  Vector3 blur_radii =
      effect_transform.Basis() * Vector3{blur_radius.x, blur_radius.y, 0.0};
  return output_limit.Expand(Point(blur_radii.x, blur_radii.y));
}

References impeller::Matrix::Basis(), blur_radius, CalculateBlurRadius(), impeller::TRect< T >::Expand(), scaled_sigma, ScaleSigma(), impeller::TPoint< T >::x, impeller::Vector3::x, impeller::TPoint< T >::y, and impeller::Vector3::y.

GetSigmaX()

Scalar impeller::GaussianBlurFilterContents::GetSigmaX ( ) const

inline

Definition at line 64 of file gaussian_blur_filter_contents.h.

{ return sigma_.x; }

References impeller::TPoint< T >::x.

Referenced by impeller::testing::TEST().

GetSigmaY()

Scalar impeller::GaussianBlurFilterContents::GetSigmaY ( ) const

inline

Definition at line 65 of file gaussian_blur_filter_contents.h.

{ return sigma_.y; }

References impeller::TPoint< T >::y.

Referenced by impeller::testing::TEST().

ScaleSigma()

Scalar impeller::GaussianBlurFilterContents::ScaleSigma ( Scalar  sigma )

static

Scales down the sigma value to match Skia's behavior.

effective_blur_radius = CalculateBlurRadius(ScaleSigma(sigma_));

This function was calculated by observing Skia's behavior. Its blur at 500 seemed to be 0.15. Since we clamp at 500 I solved the quadratic equation that puts the minima there and a f(0)=1.

Definition at line 902 of file gaussian_blur_filter_contents.cc.

                                                          {
  // Limit the kernel size to 1000x1000 pixels, like Skia does.
  Scalar clamped = std::min(sigma, kMaxSigma);
  constexpr Scalar a = 3.4e-06;
  constexpr Scalar b = -3.4e-3;
  constexpr Scalar c = 1.f;
  Scalar scalar = c + b * clamped + a * clamped * clamped;
  return clamped * scalar;
}

Referenced by GetFilterSourceCoverage(), and impeller::testing::TEST().

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

• impeller/entity/contents/filters/gaussian_blur_filter_contents.h
• impeller/entity/contents/filters/gaussian_blur_filter_contents.cc