overlayContainerDataSource.h

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//
// Copyright 2021 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_IMAGING_HD_OVERLAY_CONTAINER_DATA_SOURCE_H
#define PXR_IMAGING_HD_OVERLAY_CONTAINER_DATA_SOURCE_H

#include "pxr/imaging/hd/dataSource.h"

PXR_NAMESPACE_OPEN_SCOPE

/// \class HdOverlayContainerDataSource
///
/// Lazily composes two or more container source hierarchies
/// Earlier entries on the containers array have stronger opinion strength
/// for overlapping child names. Overlapping children which are all containers
/// themselves are returned as another instance of this class
class HdOverlayContainerDataSource : public HdContainerDataSource
{
public:
    HD_DECLARE_DATASOURCE(HdOverlayContainerDataSource);

    HD_DECLARE_DATASOURCE_INITIALIZER_LIST_NEW(
            HdOverlayContainerDataSource, 
            HdContainerDataSourceHandle);

    HD_API
    HdOverlayContainerDataSource(
        std::initializer_list<HdContainerDataSourceHandle> sources);

    HD_API
    HdOverlayContainerDataSource(
        size_t count,
        HdContainerDataSourceHandle *containers);

    HD_API
    HdOverlayContainerDataSource(
        const HdContainerDataSourceHandle &src1,
        const HdContainerDataSourceHandle &src2);

    HD_API
    HdOverlayContainerDataSource(
        const HdContainerDataSourceHandle &src1,
        const HdContainerDataSourceHandle &src2,
        const HdContainerDataSourceHandle &src3);
    
    /// Creates HdOverlayContainerDataSource from sources, but only
    /// if needed. If one of given handles is null, the other handle
    /// is returned instead.
    HD_API
    static
    HdContainerDataSourceHandle
    OverlayedContainerDataSources(
        const HdContainerDataSourceHandle &src1,
        const HdContainerDataSourceHandle &src2);

    HD_API
    TfTokenVector GetNames() override;
    HD_API
    HdDataSourceBaseHandle Get(const TfToken &name) override;

private:
    using _ContainerVector = TfSmallVector<HdContainerDataSourceHandle, 8>;
    _ContainerVector _containers;
};

HD_DECLARE_DATASOURCE_HANDLES(HdOverlayContainerDataSource);

PXR_NAMESPACE_CLOSE_SCOPE

#endif