third_party/WebKit/Source/platform/graphics/CompositorMutableStateProvider.cpp

// Copyright 2016 The Chromium 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 "platform/graphics/CompositorMutableStateProvider.h"

#include "cc/layers/layer_impl.h"
#include "cc/trees/layer_tree_impl.h"
#include "platform/graphics/CompositorElementId.h"
#include "platform/graphics/CompositorMutableProperties.h"
#include "platform/graphics/CompositorMutableState.h"
#include "platform/graphics/CompositorMutation.h"
#include "wtf/PtrUtil.h"
#include <memory>

namespace blink {

CompositorMutableStateProvider::CompositorMutableStateProvider(
    cc::LayerTreeImpl* treeImpl,
    CompositorMutations* mutations)
    : m_tree(treeImpl), m_mutations(mutations) {}

CompositorMutableStateProvider::~CompositorMutableStateProvider() {}

std::unique_ptr<CompositorMutableState>
CompositorMutableStateProvider::getMutableStateFor(uint64_t elementId) {
  cc::LayerImpl* mainLayer = m_tree->LayerByElementId(
      createCompositorElementId(elementId, CompositorSubElementId::Primary));
  cc::LayerImpl* scrollLayer = m_tree->LayerByElementId(
      createCompositorElementId(elementId, CompositorSubElementId::Scroll));

  if (!mainLayer && !scrollLayer)
    return nullptr;

  // Ensure that we have an entry in the map for |elementId| but do as few
  // allocations and queries as possible. This will update the map only if we
  // have not added a value for |elementId|.
  auto result = m_mutations->map.add(elementId, nullptr);

  // Only if this is a new entry do we want to allocate a new mutation.
  if (result.isNewEntry)
    result.storedValue->value = wrapUnique(new CompositorMutation);

  return wrapUnique(new CompositorMutableState(result.storedValue->value.get(),
                                               mainLayer, scrollLayer));
}

}  // namespace blink