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For https://github.com/flutter/flutter/issues/33807 We still need to make layers' children immutable for full immutability. That will require us to change the SceneBuilder API to build the layer bottom up instead of top down (post-order traversal instead of pre-order traversal).
48 lines
1.6 KiB
C++
48 lines
1.6 KiB
C++
// Copyright 2013 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_
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#define FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_
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#include "flutter/flow/layers/container_layer.h"
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namespace flutter {
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// Don't add an OpacityLayer with no children to the layer tree. Painting an
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// OpacityLayer is very costly due to the saveLayer call. If there's no child,
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// having the OpacityLayer or not has the same effect. In debug_unopt build, the
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// |EnsureSingleChild| will assert if there are no children.
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class OpacityLayer : public ContainerLayer {
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public:
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OpacityLayer(int alpha, const SkPoint& offset);
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~OpacityLayer() override;
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void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
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void Paint(PaintContext& context) const override;
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// TODO(chinmaygarde): Once SCN-139 is addressed, introduce a new node in the
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// session scene hierarchy.
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private:
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int alpha_;
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SkPoint offset_;
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// Restructure (if necessary) OpacityLayer to have only one child.
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//
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// This is needed to ensure that retained rendering can always be applied to
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// save the costly saveLayer.
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//
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// If there are multiple children, this creates a new identity TransformLayer,
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// sets all children to be the TransformLayer's children, and sets that
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// TransformLayer as the single child of this OpacityLayer.
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void EnsureSingleChild();
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FML_DISALLOW_COPY_AND_ASSIGN(OpacityLayer);
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};
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} // namespace flutter
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#endif // FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_
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