// 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.

#ifndef FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_
#define FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_

#include "flutter/flow/layers/elevated_container_layer.h"
#if defined(OS_FUCHSIA)
#include "flutter/flow/layers/fuchsia_system_composited_layer.h"
#endif

namespace flutter {

#if !defined(OS_FUCHSIA)
class OpacityLayerBase : public ContainerLayer {
 public:
  static bool can_system_composite() { return false; }

  OpacityLayerBase(SkColor color, SkAlpha opacity, float elevation)
      : color_(color), opacity_(opacity) {}

  void Preroll(PrerollContext* context, const SkMatrix& matrix) override;

  void set_dimensions(SkRRect rrect) {}

  SkColor color() const { return color_; }
  SkAlpha opacity() const { return opacity_; }
  float elevation() const { return 0; }

 private:
  SkColor color_;
  SkAlpha opacity_;
};
#else
using OpacityLayerBase = FuchsiaSystemCompositedLayer;
#endif

// Don't add an OpacityLayer with no children to the layer tree. Painting an
// OpacityLayer is very costly due to the saveLayer call. If there's no child,
// having the OpacityLayer or not has the same effect. In debug_unopt build,
// |Preroll| will assert if there are no children.
class OpacityLayer : public OpacityLayerBase {
 public:
  // An offset is provided here because OpacityLayer.addToScene method in the
  // Flutter framework can take an optional offset argument.
  //
  // By default, that offset is always zero, and all the offsets are handled by
  // some parent TransformLayers. But we allow the offset to be non-zero for
  // backward compatibility. If it's non-zero, the old behavior is to propage
  // that offset to all the leaf layers (e.g., PictureLayer). That will make
  // the retained rendering inefficient as a small offset change could propagate
  // to many leaf layers. Therefore we try to capture that offset here to stop
  // the propagation as repainting the OpacityLayer is expensive.
  OpacityLayer(SkAlpha alpha, const SkPoint& offset);

  void Add(std::shared_ptr<Layer> layer) override;

  void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
#if defined(OS_FUCHSIA)
  void UpdateScene(SceneUpdateContext& context) override;
#endif
  void Paint(PaintContext& context) const override;

 private:
  ContainerLayer* GetChildContainer() const;

  SkPoint offset_;

  FML_DISALLOW_COPY_AND_ASSIGN(OpacityLayer);
};

}  // namespace flutter

#endif  // FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_