flow/layers/container_layer.cc

// 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 "flutter/flow/layers/container_layer.h"

#include <optional>

namespace flutter {

ContainerLayer::ContainerLayer() {}

void ContainerLayer::Add(std::shared_ptr<Layer> layer) {
  layers_.emplace_back(std::move(layer));
}

void ContainerLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
  TRACE_EVENT0("flutter", "ContainerLayer::Preroll");

  SkRect child_paint_bounds = SkRect::MakeEmpty();
  PrerollChildren(context, matrix, &child_paint_bounds);
  set_paint_bounds(child_paint_bounds);
}

void ContainerLayer::Paint(PaintContext& context) const {
  FML_DCHECK(needs_painting(context));

  PaintChildren(context);
}

void ContainerLayer::PrerollChildren(PrerollContext* context,
                                     const SkMatrix& child_matrix,
                                     SkRect* child_paint_bounds) {
#if defined(LEGACY_FUCHSIA_EMBEDDER)
  // If there is embedded Fuchsia content in the scene (a ChildSceneLayer),
  // Layers that appear above the embedded content will be turned into their own
  // Scenic layers.
  child_layer_exists_below_ = context->child_scene_layer_exists_below;
  context->child_scene_layer_exists_below = false;
#endif

  // Platform views have no children, so context->has_platform_view should
  // always be false.
  FML_DCHECK(!context->has_platform_view);
  bool child_has_platform_view = false;
  for (auto& layer : layers_) {
    // Reset context->has_platform_view to false so that layers aren't treated
    // as if they have a platform view based on one being previously found in a
    // sibling tree.
    context->has_platform_view = false;

    layer->Preroll(context, child_matrix);

    if (layer->needs_system_composite()) {
      set_needs_system_composite(true);
    }
    child_paint_bounds->join(layer->paint_bounds());

    child_has_platform_view =
        child_has_platform_view || context->has_platform_view;
  }

  context->has_platform_view = child_has_platform_view;

#if defined(LEGACY_FUCHSIA_EMBEDDER)
  if (child_layer_exists_below_) {
    set_needs_system_composite(true);
  }
  context->child_scene_layer_exists_below =
      context->child_scene_layer_exists_below || child_layer_exists_below_;
#endif
}

void ContainerLayer::PaintChildren(PaintContext& context) const {
  // We can no longer call FML_DCHECK here on the needs_painting(context)
  // condition as that test is only valid for the PaintContext that
  // is initially handed to a layer's Paint() method. By the time the
  // layer calls PaintChildren(), though, it may have modified the
  // PaintContext so the test doesn't work in this "context".

  // Intentionally not tracing here as there should be no self-time
  // and the trace event on this common function has a small overhead.
  for (auto& layer : layers_) {
    if (layer->needs_painting(context)) {
      layer->Paint(context);
    }
  }
}

void ContainerLayer::TryToPrepareRasterCache(PrerollContext* context,
                                             Layer* layer,
                                             const SkMatrix& matrix) {
  if (!context->has_platform_view && context->raster_cache &&
      SkRect::Intersects(context->cull_rect, layer->paint_bounds())) {
    context->raster_cache->Prepare(context, layer, matrix);
  }
}

#if defined(LEGACY_FUCHSIA_EMBEDDER)

void ContainerLayer::CheckForChildLayerBelow(PrerollContext* context) {
  // All ContainerLayers make the check in PrerollChildren.
}

void ContainerLayer::UpdateScene(std::shared_ptr<SceneUpdateContext> context) {
  UpdateSceneChildren(context);
}

void ContainerLayer::UpdateSceneChildren(
    std::shared_ptr<SceneUpdateContext> context) {
  FML_DCHECK(needs_system_composite());

  std::optional<SceneUpdateContext::Frame> frame;
  if (child_layer_exists_below_) {
    frame.emplace(
        context, SkRRect::MakeRect(paint_bounds()), SK_ColorTRANSPARENT,
        SkScalarRoundToInt(context->alphaf() * 255), "flutter::Layer");
    frame->AddPaintLayer(this);
  }

  for (auto& layer : layers_) {
    if (layer->needs_system_composite()) {
      layer->UpdateScene(context);
    }
  }
}

#endif

MergedContainerLayer::MergedContainerLayer() {
  // Ensure the layer has only one direct child.
  //
  // Any children will actually be added as children of this empty
  // ContainerLayer which can be accessed via ::GetContainerLayer().
  // If only one child is ever added to this layer then that child
  // will become the layer returned from ::GetCacheableChild().
  // If multiple child layers are added, then this implicit container
  // child becomes the cacheable child, but at the potential cost of
  // not being as stable in the raster cache from frame to frame.
  ContainerLayer::Add(std::make_shared<ContainerLayer>());
}

void MergedContainerLayer::Add(std::shared_ptr<Layer> layer) {
  GetChildContainer()->Add(std::move(layer));
}

ContainerLayer* MergedContainerLayer::GetChildContainer() const {
  FML_DCHECK(layers().size() == 1);

  return static_cast<ContainerLayer*>(layers()[0].get());
}

Layer* MergedContainerLayer::GetCacheableChild() const {
  ContainerLayer* child_container = GetChildContainer();
  if (child_container->layers().size() == 1) {
    return child_container->layers()[0].get();
  }

  return child_container;
}

}  // namespace flutter