primDataSourceOverlayCache.h

//
// Copyright 2021 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_IMAGING_HD_PRIM_DATA_SOURCE_OVERLAY_CACHE_H
#define PXR_IMAGING_HD_PRIM_DATA_SOURCE_OVERLAY_CACHE_H
 
#include "pxr/imaging/hd/sceneIndex.h"
#include "pxr/imaging/hd/dataSource.h"
 
#include "pxr/usd/sdf/pathTable.h"
 
PXR_NAMESPACE_OPEN_SCOPE
 
// ----------------------------------------------------------------------------
 
// A utility class to handle caching of datasource overlays, along with
// invalidation functions to clear the cache.
 
class HdPrimDataSourceOverlayCache :
    public std::enable_shared_from_this<HdPrimDataSourceOverlayCache>
{
public:
    virtual ~HdPrimDataSourceOverlayCache();
 
    HdSceneIndexPrim GetPrim(const SdfPath &primPath) const;
 
    void HandlePrimsAdded(
        const HdSceneIndexObserver::AddedPrimEntries &entries,
        const HdSceneIndexBaseRefPtr &source);
    void HandlePrimsRemoved(
        const HdSceneIndexObserver::RemovedPrimEntries &entries);
    void HandlePrimsDirtied(
        const HdSceneIndexObserver::DirtiedPrimEntries &entries,
        HdSceneIndexObserver::DirtiedPrimEntries *additionalDirtied);
 
protected:
    HdPrimDataSourceOverlayCache() = default;
 
    // This struct provides a way for users of the cache to describe the
    // structure of synthetic attributes. For example, if you compute
    // "xformInverse" from "xform", the topology would look like:
    // OverlayTopology topo = { "xformInverse" ->
    //   { .onPrim = { "xform" }, .onParent = { }, false }
    // }
    // ... notably, this tells us what attributes we're adding (xformInverse,
    // but only when xform is present); and also to dirty xformInverse when
    // xform is dirty.
    //
    // For attributes we always want to add (even if their dependents are not
    // present), dependenciesOptional lets us say as much.
    //
    // Note: _ComputeOverlayDataSource should respect this topology, or behavior
    // is undefined...
    //
    // XXX: the "onParent" dependencies here are to support eventual inherited
    // attribute caching, but this feature hasn't been implemented yet.
    struct _OverlayDependencies
    {
        _OverlayDependencies()
            : onPrim(), onParent(), dependenciesOptional(false) {}
 
        HdDataSourceLocatorSet onPrim;
        HdDataSourceLocatorSet onParent;
        bool dependenciesOptional;
    };
    using _OverlayTopology = std::map<TfToken, _OverlayDependencies>;
 
 
    // Topology should be set once, from the derived class constructor.
    void _SetOverlayTopology(const _OverlayTopology &topology) {
        _overlayTopology = topology;
    }
 
    // Compute the named datasource. Note that inputDataSource comes from the
    // source scene index, while parentOverlayDataSource comes from the cache
    // and is consequently recursively composed.
    //
    // XXX: the "parentOverlayDataSource" is here to support eventual inherited
    // attribute caching, but this feature hasn't been implemented yet. For now,
    // it will always be null.
    virtual HdDataSourceBaseHandle _ComputeOverlayDataSource(
        const TfToken &name,
        HdContainerDataSourceHandle inputDataSource,
        HdContainerDataSourceHandle parentOverlayDataSource) const = 0;
 
private:
    class _HdPrimDataSourceOverlay : public HdContainerDataSource
    {
    public:
        HD_DECLARE_DATASOURCE(_HdPrimDataSourceOverlay);
 
        _HdPrimDataSourceOverlay(
            HdContainerDataSourceHandle inputDataSource,
            HdContainerDataSourceHandle parentOverlayDataSource,
            const std::weak_ptr<const HdPrimDataSourceOverlayCache> cache);
 
        void UpdateInputDataSource(HdContainerDataSourceHandle inputDataSource);
 
        void PrimDirtied(const HdDataSourceLocatorSet &dirtyAttributes);
 
        TfTokenVector GetNames() override;
        HdDataSourceBaseHandle Get(const TfToken &name) override;
 
    private:
        HdContainerDataSourceHandle _inputDataSource;
        HdContainerDataSourceHandle _parentOverlayDataSource;
        const std::weak_ptr<const HdPrimDataSourceOverlayCache> _cache;
 
        using _OverlayMap = std::map<TfToken, HdDataSourceBaseHandle>;
 
        _OverlayMap _overlayMap;
    };
 
    SdfPathTable<HdSceneIndexPrim> _cache;
    _OverlayTopology _overlayTopology;
};
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif