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/CompositorMutableState.h"
#include "platform/graphics/CompositorMutation.h"
#include "wtf/PassOwnPtr.h"
#include "wtf/PtrUtil.h"

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::LayerTreeImpl::ElementLayers layers = m_tree->GetMutableLayers(elementId);

    if (!layers.main && !layers.scroll)
        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 = adoptPtr(new CompositorMutation);

    return wrapUnique(new CompositorMutableState(result.storedValue->value.get(), layers.main, layers.scroll));
}

} // namespace blink