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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.
#ifndef FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_
#define FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_
#include "flutter/flow/layers/container_layer.h"
namespace flutter {
// 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 MergedContainerLayer {
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 Diff(DiffContext* context, const Layer* old_layer) override;
void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
void Paint(PaintContext& context) const override;
// Returns whether the children are capable of inheriting an opacity value
// and modifying their rendering accordingly. This value is only guaranteed
// to be valid after the local |Preroll| method is called.
bool children_can_accept_opacity() const {
return children_can_accept_opacity_;
}
void set_children_can_accept_opacity(bool value) {
children_can_accept_opacity_ = value;
}
SkScalar opacity() const { return alpha_ * 1.0 / SK_AlphaOPAQUE; }
private:
SkAlpha alpha_;
SkPoint offset_;
bool children_can_accept_opacity_;
FML_DISALLOW_COPY_AND_ASSIGN(OpacityLayer);
};
} // namespace flutter
#endif // FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_