1 // Copyright 2013 The Flutter Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_ 6 #define FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_ 7 8 #include "flutter/flow/layers/container_layer.h" 9 10 namespace flutter { 11 12 // Don't add an OpacityLayer with no children to the layer tree. Painting an 13 // OpacityLayer is very costly due to the saveLayer call. If there's no child, 14 // having the OpacityLayer or not has the same effect. In debug_unopt build, the 15 // |EnsureSingleChild| will assert if there are no children. 16 class OpacityLayer : public ContainerLayer { 17 public: 18 // An offset is provided here because OpacityLayer.addToScene method in the 19 // Flutter framework can take an optional offset argument. 20 // 21 // By default, that offset is always zero, and all the offsets are handled by 22 // some parent TransformLayers. But we allow the offset to be non-zero for 23 // backward compatibility. If it's non-zero, the old behavior is to propage 24 // that offset to all the leaf layers (e.g., PictureLayer). That will make 25 // the retained rendering inefficient as a small offset change could propagate 26 // to many leaf layers. Therefore we try to capture that offset here to stop 27 // the propagation as repainting the OpacityLayer is expensive. 28 OpacityLayer(int alpha, const SkPoint& offset); 29 ~OpacityLayer() override; 30 31 void Preroll(PrerollContext* context, const SkMatrix& matrix) override; 32 33 void Paint(PaintContext& context) const override; 34 35 // TODO(chinmaygarde): Once SCN-139 is addressed, introduce a new node in the 36 // session scene hierarchy. 37 38 private: 39 int alpha_; 40 SkPoint offset_; 41 42 // Restructure (if necessary) OpacityLayer to have only one child. 43 // 44 // This is needed to ensure that retained rendering can always be applied to 45 // save the costly saveLayer. 46 // 47 // If there are multiple children, this creates a new identity TransformLayer, 48 // sets all children to be the TransformLayer's children, and sets that 49 // TransformLayer as the single child of this OpacityLayer. 50 void EnsureSingleChild(); 51 52 FML_DISALLOW_COPY_AND_ASSIGN(OpacityLayer); 53 }; 54 55 } // namespace flutter 56 57 #endif // FLUTTER_FLOW_LAYERS_OPACITY_LAYER_H_ 58