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 std::shared_ptr< Geometry > &mask_geometry)
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.
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.
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="Filter Snapshot") 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).
const FilterContents *	AsFilter () const override
	Cast to a filter. Returns nullptr if this Contents is not a filter.
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 bool	IsTranslationOnly () const
	Returns true if this filter graph doesn't perform any basis transforms to the filtered content. For example: Rotating, scaling, and skewing are all basis transforms, but translating is not.
bool	IsLeaf () const
	Returns true if this filter does not have any FilterInput children.
void	SetLeafInputs (const FilterInput::Vector &inputs)
	Replaces the set of all leaf FilterContents with a new set of FilterInputs.
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
	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.
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.
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.
void	SetColorSourceSize (Size size)
virtual bool	CanInheritOpacity (const Entity &entity) const
	Whether or not this contents can accept the opacity peephole optimization.
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 std::shared_ptr< 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 Public Member Functions inherited from impeller::Contents
static std::shared_ptr< Contents >	MakeAnonymous (RenderProc render_proc, CoverageProc coverage_proc)

Static Public Attributes
static std::string_view	kNoMipsError
static const int32_t	kBlurFilterRequiredMipCount = 4
Static Public Attributes inherited from impeller::FilterContents
static const int32_t	kBlurFilterRequiredMipCount

Private Member Functions
std::optional< Entity >	RenderFilter (const FilterInput::Vector &input_textures, const ContentContext &renderer, const Entity &entity, const Matrix &effect_transform, const Rect &coverage, const std::optional< Rect > &coverage_hint) const override
	Converts zero or more filter inputs into a render instruction.

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)>

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 34 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 std::shared_ptr< Geometry > &  mask_geometry  )

explicit

Definition at line 297 of file gaussian_blur_filter_contents.cc.

    : sigma_x_(sigma_x),
      sigma_y_(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);
}

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 563 of file gaussian_blur_filter_contents.cc.

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

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 315 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;
};

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 567 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);
}

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 353 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 {};
  }
 
  Vector2 scaled_sigma = (effect_transform.Basis() *
                          Vector2(ScaleSigma(sigma_x_), ScaleSigma(sigma_y_)))
                             .Abs();
  Vector2 blur_radius = Vector2(CalculateBlurRadius(scaled_sigma.x),
                                CalculateBlurRadius(scaled_sigma.y));
  Vector2 padding(ceil(blur_radius.x), ceil(blur_radius.y));
  Vector2 local_padding = (entity.GetTransform().Basis() * padding).Abs();
  return input_coverage.value().Expand(Point(local_padding.x, local_padding.y));
}

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 342 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));
}

GetSigmaX()

Scalar impeller::GaussianBlurFilterContents::GetSigmaX ( ) const

inline

Definition at line 46 of file gaussian_blur_filter_contents.h.

{ return sigma_x_; }

GetSigmaY()

Scalar impeller::GaussianBlurFilterContents::GetSigmaY ( ) const

inline

Definition at line 47 of file gaussian_blur_filter_contents.h.

{ return sigma_y_; }

RenderFilter()

std::optional< Entity > impeller::GaussianBlurFilterContents::RenderFilter ( const FilterInput::Vector &  inputs, const ContentContext &  renderer, const Entity &  entity, const Matrix &  effect_transform, const Rect &  coverage, const std::optional< Rect > &  coverage_hint  ) const

overrideprivatevirtual

Converts zero or more filter inputs into a render instruction.

Implements impeller::FilterContents.

Definition at line 376 of file gaussian_blur_filter_contents.cc.

                                                  {
  if (inputs.empty()) {
    return std::nullopt;
  }
 
  Vector2 scaled_sigma = (effect_transform.Basis() *
                          Vector2(ScaleSigma(sigma_x_), ScaleSigma(sigma_y_)))
                             .Abs();
  Vector2 blur_radius = Vector2(CalculateBlurRadius(scaled_sigma.x),
                                CalculateBlurRadius(scaled_sigma.y));
  Vector2 padding(ceil(blur_radius.x), ceil(blur_radius.y));
  Vector2 local_padding = (entity.GetTransform().Basis() * padding).Abs();
 
  // Apply as much of the desired padding as possible from the source. This may
  // be ignored so must be accounted for in the downsample pass by adding a
  // transparent gutter.
  std::optional<Rect> expanded_coverage_hint;
  if (coverage_hint.has_value()) {
    expanded_coverage_hint = coverage_hint->Expand(local_padding);
  }
 
  int32_t mip_count = kBlurFilterRequiredMipCount;
  if (renderer.GetContext()->GetBackendType() ==
      Context::BackendType::kOpenGLES) {
    // TODO(https://github.com/flutter/flutter/issues/141732): Implement mip map
    // generation on opengles.
    mip_count = 1;
  }
 
  std::optional<Snapshot> input_snapshot =
      inputs[0]->GetSnapshot("GaussianBlur", renderer, entity,
                             /*coverage_limit=*/expanded_coverage_hint,
                             /*mip_count=*/mip_count);
  if (!input_snapshot.has_value()) {
    return std::nullopt;
  }
 
  if (scaled_sigma.x < kEhCloseEnough && scaled_sigma.y < kEhCloseEnough) {
    return Entity::FromSnapshot(input_snapshot.value(),
                                entity.GetBlendMode());  // No blur to render.
  }
 
  // In order to avoid shimmering in downsampling step, we should have mips.
  if (input_snapshot->texture->GetMipCount() <= 1) {
    FML_DLOG(ERROR) << kNoMipsError;
  }
  FML_DCHECK(!input_snapshot->texture->NeedsMipmapGeneration());
 
  Scalar desired_scalar =
      std::min(CalculateScale(scaled_sigma.x), CalculateScale(scaled_sigma.y));
  // TODO(jonahwilliams): If desired_scalar is 1.0 and we fully acquired the
  // gutter from the expanded_coverage_hint, we can skip the downsample pass.
  // pass.
  Vector2 downsample_scalar(desired_scalar, desired_scalar);
  Rect source_rect = Rect::MakeSize(input_snapshot->texture->GetSize());
  Rect source_rect_padded = source_rect.Expand(padding);
  Matrix padding_snapshot_adjustment = Matrix::MakeTranslation(-padding);
  // TODO(gaaclarke): The padding could be removed if we know it's not needed or
  //   resized to account for the expanded_clip_coverage. There doesn't appear
  //   to be the math to make those calculations though. The following
  //   optimization works, but causes a shimmer as a result of
  //   https://github.com/flutter/flutter/issues/140193 so it isn't applied.
  //
  //   !input_snapshot->GetCoverage()->Expand(-local_padding)
  //     .Contains(coverage_hint.value()))
  Vector2 downsampled_size = source_rect_padded.GetSize() * downsample_scalar;
  ISize subpass_size =
      ISize(round(downsampled_size.x), round(downsampled_size.y));
  Vector2 effective_scalar =
      Vector2(subpass_size) / source_rect_padded.GetSize();
 
  Quad uvs = CalculateUVs(inputs[0], entity, source_rect_padded,
                          input_snapshot->texture->GetSize());
 
  std::shared_ptr<CommandBuffer> command_buffer =
      renderer.GetContext()->CreateCommandBuffer();
  if (!command_buffer) {
    return std::nullopt;
  }
 
  fml::StatusOr<RenderTarget> pass1_out = MakeDownsampleSubpass(
      renderer, command_buffer, input_snapshot->texture,
      input_snapshot->sampler_descriptor, uvs, subpass_size, tile_mode_);
 
  if (!pass1_out.ok()) {
    return std::nullopt;
  }
 
  Vector2 pass1_pixel_size =
      1.0 / Vector2(pass1_out.value().GetRenderTargetTexture()->GetSize());
 
  std::optional<Rect> input_snapshot_coverage = input_snapshot->GetCoverage();
  Quad blur_uvs = {Point(0, 0), Point(1, 0), Point(0, 1), Point(1, 1)};
  if (expanded_coverage_hint.has_value() &&
      input_snapshot_coverage.has_value() &&
      // TODO(https://github.com/flutter/flutter/issues/140890): Remove this
      //   condition. There is some flaw in coverage stopping us from using this
      //   today. I attempted to use source coordinates to calculate the uvs,
      //   but that didn't work either.
      input_snapshot.has_value() &&
      input_snapshot.value().transform.IsTranslationScaleOnly()) {
    // Only process the uvs where the blur is happening, not the whole texture.
    std::optional<Rect> uvs = MakeReferenceUVs(input_snapshot_coverage.value(),
                                               expanded_coverage_hint.value())
                                  .Intersection(Rect::MakeSize(Size(1, 1)));
    FML_DCHECK(uvs.has_value());
    if (uvs.has_value()) {
      blur_uvs[0] = uvs->GetLeftTop();
      blur_uvs[1] = uvs->GetRightTop();
      blur_uvs[2] = uvs->GetLeftBottom();
      blur_uvs[3] = uvs->GetRightBottom();
    }
  }
 
  fml::StatusOr<RenderTarget> pass2_out = MakeBlurSubpass(
      renderer, command_buffer, /*input_pass=*/pass1_out.value(),
      input_snapshot->sampler_descriptor, tile_mode_,
      BlurParameters{
          .blur_uv_offset = Point(0.0, pass1_pixel_size.y),
          .blur_sigma = scaled_sigma.y * effective_scalar.y,
          .blur_radius = ScaleBlurRadius(blur_radius.y, effective_scalar.y),
          .step_size = 1,
      },
      /*destination_target=*/std::nullopt, blur_uvs);
 
  if (!pass2_out.ok()) {
    return std::nullopt;
  }
 
  // Only ping pong if the first pass actually created a render target.
  auto pass3_destination = pass2_out.value().GetRenderTargetTexture() !=
                                   pass1_out.value().GetRenderTargetTexture()
                               ? std::optional<RenderTarget>(pass1_out.value())
                               : std::optional<RenderTarget>(std::nullopt);
 
  fml::StatusOr<RenderTarget> pass3_out = MakeBlurSubpass(
      renderer, command_buffer, /*input_pass=*/pass2_out.value(),
      input_snapshot->sampler_descriptor, tile_mode_,
      BlurParameters{
          .blur_uv_offset = Point(pass1_pixel_size.x, 0.0),
          .blur_sigma = scaled_sigma.x * effective_scalar.x,
          .blur_radius = ScaleBlurRadius(blur_radius.x, effective_scalar.x),
          .step_size = 1,
      },
      pass3_destination, blur_uvs);
 
  if (!pass3_out.ok()) {
    return std::nullopt;
  }
 
  if (!renderer.GetContext()
           ->GetCommandQueue()
           ->Submit(/*buffers=*/{command_buffer})
           .ok()) {
    return std::nullopt;
  }
 
  // The ping-pong approach requires that each render pass output has the same
  // size.
  FML_DCHECK((pass1_out.value().GetRenderTargetSize() ==
              pass2_out.value().GetRenderTargetSize()) &&
             (pass2_out.value().GetRenderTargetSize() ==
              pass3_out.value().GetRenderTargetSize()));
 
  SamplerDescriptor sampler_desc = MakeSamplerDescriptor(
      MinMagFilter::kLinear, SamplerAddressMode::kClampToEdge);
 
  Entity blur_output_entity = Entity::FromSnapshot(
      Snapshot{.texture = pass3_out.value().GetRenderTargetTexture(),
               .transform = input_snapshot->transform *
                            padding_snapshot_adjustment *
                            Matrix::MakeScale(1 / effective_scalar),
               .sampler_descriptor = sampler_desc,
               .opacity = input_snapshot->opacity},
      entity.GetBlendMode());
 
  return ApplyBlurStyle(mask_blur_style_, entity, inputs[0],
                        input_snapshot.value(), std::move(blur_output_entity),
                        mask_geometry_);
}

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 583 of file gaussian_blur_filter_contents.cc.

                                                          {
  // Limit the kernel size to 1000x1000 pixels, like Skia does.
  Scalar clamped = std::min(sigma, 500.0f);
  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;
}

Member Data Documentation

kBlurFilterRequiredMipCount

const int32_t impeller::GaussianBlurFilterContents::kBlurFilterRequiredMipCount = 4

static

Definition at line 37 of file gaussian_blur_filter_contents.h.

kNoMipsError

std::string_view impeller::GaussianBlurFilterContents::kNoMipsError

static

Initial value:

=
    "Applying gaussian blur without mipmap."

Definition at line 36 of file gaussian_blur_filter_contents.h.

---

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