directional_gaussian_blur_filter_contents.cc

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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#include "impeller/entity/contents/filters/directional_gaussian_blur_filter_contents.h"
 
#include <cmath>
#include <utility>
 
#include "impeller/base/strings.h"
#include "impeller/core/formats.h"
#include "impeller/core/sampler_descriptor.h"
#include "impeller/entity/contents/content_context.h"
#include "impeller/entity/contents/filters/filter_contents.h"
#include "impeller/geometry/rect.h"
#include "impeller/geometry/scalar.h"
#include "impeller/renderer/command_buffer.h"
#include "impeller/renderer/render_pass.h"
#include "impeller/renderer/render_target.h"
#include "impeller/renderer/vertex_buffer_builder.h"
 
namespace impeller {
 
// 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.
Sigma ScaleSigma(Sigma sigma) {
  // Limit the kernel size to 1000x1000 pixels, like Skia does.
  Scalar clamped = std::min(sigma.sigma, 500.0f);
  Scalar scalar = 1.0 - 3.4e-3 * clamped + 3.4e-06 * clamped * clamped;
  return Sigma(clamped * scalar);
}
 
DirectionalGaussianBlurFilterContents::DirectionalGaussianBlurFilterContents() =
    default;
 
DirectionalGaussianBlurFilterContents::
    ~DirectionalGaussianBlurFilterContents() = default;
 
void DirectionalGaussianBlurFilterContents::SetSigma(Sigma sigma) {
  blur_sigma_ = sigma;
}
 
void DirectionalGaussianBlurFilterContents::SetSecondarySigma(Sigma sigma) {
  secondary_blur_sigma_ = sigma;
}
 
void DirectionalGaussianBlurFilterContents::SetDirection(Vector2 direction) {
  blur_direction_ = direction.Normalize();
  if (blur_direction_.IsZero()) {
    blur_direction_ = Vector2(0, 1);
  }
}
 
void DirectionalGaussianBlurFilterContents::SetBlurStyle(BlurStyle blur_style) {
  blur_style_ = blur_style;
}
 
void DirectionalGaussianBlurFilterContents::SetTileMode(
    Entity::TileMode tile_mode) {
  tile_mode_ = tile_mode;
}
 
void DirectionalGaussianBlurFilterContents::SetIsSecondPass(
    bool is_second_pass) {
  is_second_pass_ = is_second_pass;
}
 
std::optional<Entity> DirectionalGaussianBlurFilterContents::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 {
  using VS = GaussianBlurPipeline::VertexShader;
  using FS = GaussianBlurPipeline::FragmentShader;
 
  //----------------------------------------------------------------------------
  /// Handle inputs.
  ///
 
  if (inputs.empty()) {
    return std::nullopt;
  }
 
  auto radius = Radius{ScaleSigma(blur_sigma_)}.radius;
 
  auto transform = entity.GetTransform() * effect_transform.Basis();
  auto transformed_blur_radius =
      transform.TransformDirection(blur_direction_ * radius);
 
  auto transformed_blur_radius_length = transformed_blur_radius.GetLength();
 
  // Input 0 snapshot.
 
  std::optional<Rect> expanded_coverage_hint;
  if (coverage_hint.has_value()) {
    auto r =
        Point(transformed_blur_radius_length, transformed_blur_radius_length)
            .Abs();
    expanded_coverage_hint =
        is_second_pass_ ? coverage_hint : coverage_hint->Expand(r);
  }
  auto input_snapshot = inputs[0]->GetSnapshot("GaussianBlur", renderer, entity,
                                               expanded_coverage_hint);
  if (!input_snapshot.has_value()) {
    return std::nullopt;
  }
 
  if (blur_sigma_.sigma < kEhCloseEnough) {
    return Entity::FromSnapshot(input_snapshot.value(), entity.GetBlendMode(),
                                entity.GetClipDepth());  // No blur to render.
  }
 
  // If the radius length is < .5, the shader will take at most 1 sample,
  // resulting in no blur.
  if (transformed_blur_radius_length < .5) {
    return Entity::FromSnapshot(input_snapshot.value(), entity.GetBlendMode(),
                                entity.GetClipDepth());  // No blur to render.
  }
 
  // A matrix that rotates the snapshot space such that the blur direction is
  // +X.
  auto texture_rotate = Matrix::MakeRotationZ(
      transformed_blur_radius.Normalize().AngleTo({1, 0}));
 
  // Converts local pass space to screen space. This is just the snapshot space
  // rotated such that the blur direction is +X.
  auto pass_transform = texture_rotate * input_snapshot->transform;
 
  // The pass texture coverage, but rotated such that the blur is in the +X
  // direction, and expanded to include the blur radius. This is used for UV
  // projection and as a source for the pass size. Note that it doesn't matter
  // which direction the space is rotated in when grabbing the pass size.
  auto pass_texture_rect = Rect::MakeSize(input_snapshot->texture->GetSize())
                               .TransformBounds(pass_transform)
                               .Expand(transformed_blur_radius_length, 0);
 
  // UV mapping.
 
  auto pass_uv_project = [&texture_rotate,
                          &pass_texture_rect](Snapshot& input) {
    auto uv_matrix = Matrix::MakeScale(1 / Vector2(input.texture->GetSize())) *
                     (texture_rotate * input.transform).Invert();
    return pass_texture_rect.GetTransformedPoints(uv_matrix);
  };
 
  auto input_uvs = pass_uv_project(input_snapshot.value());
 
  //----------------------------------------------------------------------------
  /// Render to texture.
  ///
 
  ContentContext::SubpassCallback subpass_callback = [&](const ContentContext&
                                                             renderer,
                                                         RenderPass& pass) {
    auto& host_buffer = pass.GetTransientsBuffer();
 
    VertexBufferBuilder<VS::PerVertexData> vtx_builder;
    vtx_builder.AddVertices({
        {Point(0, 0), input_uvs[0]},
        {Point(1, 0), input_uvs[1]},
        {Point(0, 1), input_uvs[2]},
        {Point(1, 1), input_uvs[3]},
    });
 
    VS::FrameInfo frame_info;
    frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
    frame_info.texture_sampler_y_coord_scale =
        input_snapshot->texture->GetYCoordScale();
 
    FS::BlurInfo frag_info;
    auto r = Radius{transformed_blur_radius_length};
    frag_info.blur_sigma = Sigma{r}.sigma;
    frag_info.blur_radius = std::round(r.radius);
    frag_info.step_size = 2.0;
 
    // The blur direction is in input UV space.
    frag_info.blur_uv_offset =
        pass_transform.Invert().TransformDirection(Vector2(1, 0)).Normalize() /
        Point(input_snapshot->GetCoverage().value().GetSize());
 
    Command cmd;
    DEBUG_COMMAND_INFO(cmd, SPrintF("Gaussian Blur Filter (Radius=%.2f)",
                                    transformed_blur_radius_length));
    cmd.BindVertices(vtx_builder.CreateVertexBuffer(host_buffer));
 
    auto options = OptionsFromPass(pass);
    options.primitive_type = PrimitiveType::kTriangleStrip;
    options.blend_mode = BlendMode::kSource;
    auto input_descriptor = input_snapshot->sampler_descriptor;
    switch (tile_mode_) {
      case Entity::TileMode::kDecal:
        if (renderer.GetDeviceCapabilities()
                .SupportsDecalSamplerAddressMode()) {
          input_descriptor.width_address_mode = SamplerAddressMode::kDecal;
          input_descriptor.height_address_mode = SamplerAddressMode::kDecal;
        }
        break;
      case Entity::TileMode::kClamp:
        input_descriptor.width_address_mode = SamplerAddressMode::kClampToEdge;
        input_descriptor.height_address_mode = SamplerAddressMode::kClampToEdge;
        break;
      case Entity::TileMode::kMirror:
        input_descriptor.width_address_mode = SamplerAddressMode::kMirror;
        input_descriptor.height_address_mode = SamplerAddressMode::kMirror;
        break;
      case Entity::TileMode::kRepeat:
        input_descriptor.width_address_mode = SamplerAddressMode::kRepeat;
        input_descriptor.height_address_mode = SamplerAddressMode::kRepeat;
        break;
    }
    input_descriptor.mag_filter = MinMagFilter::kLinear;
    input_descriptor.min_filter = MinMagFilter::kLinear;
 
    bool has_decal_specialization =
        tile_mode_ == Entity::TileMode::kDecal &&
        !renderer.GetDeviceCapabilities().SupportsDecalSamplerAddressMode();
 
    if (has_decal_specialization) {
      cmd.pipeline = renderer.GetGaussianBlurDecalPipeline(options);
    } else {
      cmd.pipeline = renderer.GetGaussianBlurPipeline(options);
    }
 
    FS::BindTextureSampler(
        cmd, input_snapshot->texture,
        renderer.GetContext()->GetSamplerLibrary()->GetSampler(
            input_descriptor));
    VS::BindFrameInfo(cmd, host_buffer.EmplaceUniform(frame_info));
    FS::BindBlurInfo(cmd, host_buffer.EmplaceUniform(frag_info));
 
    return pass.AddCommand(std::move(cmd));
  };
 
  Vector2 scale;
  auto scale_curve = [](Scalar radius) {
    constexpr Scalar decay = 4.0;   // Larger is more gradual.
    constexpr Scalar limit = 0.95;  // The maximum percentage of the scaledown.
    const Scalar curve =
        std::min(1.0, decay / (std::max(1.0f, radius) + decay - 1.0));
    return (curve - 1) * limit + 1;
  };
  {
    scale.x = scale_curve(transformed_blur_radius_length);
 
    Scalar y_radius = std::abs(pass_transform.GetDirectionScale(Vector2(
        0, !is_second_pass_ ? 1 : Radius{secondary_blur_sigma_}.radius)));
    scale.y = scale_curve(y_radius);
  }
 
  Vector2 scaled_size = pass_texture_rect.GetSize() * scale;
  ISize floored_size = ISize(scaled_size.x, scaled_size.y);
 
  fml::StatusOr<RenderTarget> render_target = renderer.MakeSubpass(
      "Directional Gaussian Blur Filter", floored_size, subpass_callback);
 
  if (!render_target.ok()) {
    return std::nullopt;
  }
 
  SamplerDescriptor sampler_desc;
  sampler_desc.min_filter = MinMagFilter::kLinear;
  sampler_desc.mag_filter = MinMagFilter::kLinear;
  sampler_desc.width_address_mode = SamplerAddressMode::kClampToEdge;
  sampler_desc.width_address_mode = SamplerAddressMode::kClampToEdge;
 
  return Entity::FromSnapshot(
      Snapshot{
          .texture = render_target.value().GetRenderTargetTexture(),
          .transform =
              texture_rotate.Invert() *
              Matrix::MakeTranslation(pass_texture_rect.GetOrigin()) *
              Matrix::MakeScale((1 / scale) * (scaled_size / floored_size)),
          .sampler_descriptor = sampler_desc,
          .opacity = input_snapshot->opacity},
      entity.GetBlendMode(), entity.GetClipDepth());
}
 
std::optional<Rect>
DirectionalGaussianBlurFilterContents::GetFilterSourceCoverage(
    const Matrix& effect_transform,
    const Rect& output_limit) const {
  auto transform = effect_transform.Basis();
  auto transformed_blur_vector =
      transform.TransformDirection(blur_direction_ * Radius{blur_sigma_}.radius)
          .Abs();
  return output_limit.Expand(transformed_blur_vector);
}
 
std::optional<Rect> DirectionalGaussianBlurFilterContents::GetFilterCoverage(
    const FilterInput::Vector& inputs,
    const Entity& entity,
    const Matrix& effect_transform) const {
  if (inputs.empty()) {
    return std::nullopt;
  }
 
  auto coverage = inputs[0]->GetCoverage(entity);
  if (!coverage.has_value()) {
    return std::nullopt;
  }
 
  auto transform = inputs[0]->GetTransform(entity) * effect_transform.Basis();
  auto transformed_blur_vector =
      transform
          .TransformDirection(blur_direction_ *
                              Radius{ScaleSigma(blur_sigma_)}.radius)
          .Abs();
  return coverage->Expand(transformed_blur_vector);
}
 
}  // namespace impeller