// 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/solid_rrect_blur_contents.h"
#include <optional>

#include "impeller/entity/contents/content_context.h"
#include "impeller/entity/entity.h"
#include "impeller/geometry/color.h"
#include "impeller/geometry/constants.h"
#include "impeller/geometry/path.h"
#include "impeller/geometry/path_builder.h"
#include "impeller/renderer/render_pass.h"
#include "impeller/renderer/vertex_buffer_builder.h"
#include "impeller/tessellator/tessellator.h"

namespace impeller {

namespace {
// Generous padding to make sure blurs with large sigmas are fully visible.
// Used to expand the geometry around the rrect.
Scalar PadForSigma(Scalar sigma) {
  return sigma * 4.0;
}
}  // namespace

SolidRRectBlurContents::SolidRRectBlurContents() = default;

SolidRRectBlurContents::~SolidRRectBlurContents() = default;

void SolidRRectBlurContents::SetRRect(std::optional<Rect> rect,
                                      Size corner_radii) {
  rect_ = rect;
  corner_radii_ = corner_radii;
}

void SolidRRectBlurContents::SetSigma(Sigma sigma) {
  sigma_ = sigma;
}

void SolidRRectBlurContents::SetColor(Color color) {
  color_ = color.Premultiply();
}

Color SolidRRectBlurContents::GetColor() const {
  return color_;
}

std::optional<Rect> SolidRRectBlurContents::GetCoverage(
    const Entity& entity) const {
  if (!rect_.has_value()) {
    return std::nullopt;
  }

  Scalar radius = PadForSigma(sigma_.sigma);

  return rect_->Expand(radius).TransformBounds(entity.GetTransform());
}

bool SolidRRectBlurContents::Render(const ContentContext& renderer,
                                    const Entity& entity,
                                    RenderPass& pass) const {
  if (!rect_.has_value()) {
    return true;
  }

  using VS = RRectBlurPipeline::VertexShader;
  using FS = RRectBlurPipeline::FragmentShader;

  VertexBufferBuilder<VS::PerVertexData> vtx_builder;

  // Clamp the max kernel width/height to 1000 to limit the extent
  // of the blur and to kEhCloseEnough to prevent NaN calculations
  // trying to evaluate a Guassian distribution with a sigma of 0.
  auto blur_sigma = std::clamp(sigma_.sigma, kEhCloseEnough, 250.0f);
  // Increase quality by making the radius a bit bigger than the typical
  // sigma->radius conversion we use for slower blurs.
  auto blur_radius = PadForSigma(blur_sigma);
  auto positive_rect = rect_->GetPositive();
  {
    auto left = -blur_radius;
    auto top = -blur_radius;
    auto right = positive_rect.GetWidth() + blur_radius;
    auto bottom = positive_rect.GetHeight() + blur_radius;

    vtx_builder.AddVertices({
        {Point(left, top)},
        {Point(right, top)},
        {Point(left, bottom)},
        {Point(right, bottom)},
    });
  }

  Command cmd;
  DEBUG_COMMAND_INFO(cmd, "RRect Shadow");
  ContentContextOptions opts = OptionsFromPassAndEntity(pass, entity);
  opts.primitive_type = PrimitiveType::kTriangleStrip;
  Color color = color_;
  if (entity.GetBlendMode() == BlendMode::kClear) {
    opts.is_for_rrect_blur_clear = true;
    color = Color::White();
  }
  cmd.pipeline = renderer.GetRRectBlurPipeline(opts);
  cmd.stencil_reference = entity.GetClipDepth();

  cmd.BindVertices(vtx_builder.CreateVertexBuffer(pass.GetTransientsBuffer()));

  VS::FrameInfo frame_info;
  frame_info.mvp = pass.GetOrthographicTransform() * entity.GetTransform() *
                   Matrix::MakeTranslation(positive_rect.GetOrigin());
  VS::BindFrameInfo(cmd, pass.GetTransientsBuffer().EmplaceUniform(frame_info));

  FS::FragInfo frag_info;
  frag_info.color = color;
  frag_info.blur_sigma = blur_sigma;
  frag_info.rect_size = Point(positive_rect.GetSize());
  frag_info.corner_radii = {std::clamp(corner_radii_.width, kEhCloseEnough,
                                       positive_rect.GetWidth() * 0.5f),
                            std::clamp(corner_radii_.width, kEhCloseEnough,
                                       positive_rect.GetHeight() * 0.5f)};
  FS::BindFragInfo(cmd, pass.GetTransientsBuffer().EmplaceUniform(frag_info));

  if (!pass.AddCommand(std::move(cmd))) {
    return false;
  }

  return true;
}

bool SolidRRectBlurContents::ApplyColorFilter(
    const ColorFilterProc& color_filter_proc) {
  color_ = color_filter_proc(color_);
  return true;
}

}  // namespace impeller