Types.h

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// Copyright Contributors to the OpenVDB Project
// SPDX-License-Identifier: MPL-2.0

#ifndef OPENVDB_TYPES_HAS_BEEN_INCLUDED
#define OPENVDB_TYPES_HAS_BEEN_INCLUDED

#include "version.h"
#include "Platform.h"
#include "TypeList.h" // backwards compat

#ifdef OPENVDB_USE_IMATH_HALF
#ifdef OPENVDB_IMATH_VERSION
#include <Imath/half.h>
#else
#include <OpenEXR/half.h>
#endif
namespace openvdb {
OPENVDB_USE_VERSION_NAMESPACE
namespace OPENVDB_VERSION_NAME {
namespace math {
using half = half;
}}}
#else
#include <openvdb/math/Half.h>
namespace openvdb {
OPENVDB_USE_VERSION_NAMESPACE
namespace OPENVDB_VERSION_NAME {
namespace math {
using half = internal::half;
}}}
#endif

#include <openvdb/math/Math.h>
#include <openvdb/math/BBox.h>
#include <openvdb/math/Quat.h>
#include <openvdb/math/Vec2.h>
#include <openvdb/math/Vec3.h>
#include <openvdb/math/Vec4.h>
#include <openvdb/math/Mat3.h>
#include <openvdb/math/Mat4.h>
#include <openvdb/math/Coord.h>
#include <cstdint>
#include <memory>
#include <type_traits>


namespace openvdb {
OPENVDB_USE_VERSION_NAMESPACE
namespace OPENVDB_VERSION_NAME {

// One-dimensional scalar types
using Index32 = uint32_t;
using Index64 = uint64_t;
using Index   = Index32;
using Int16   = int16_t;
using Int32   = int32_t;
using Int64   = int64_t;
using Int     = Int32;
using Byte    = unsigned char;
using Real    = double;

// Two-dimensional vector types
using Vec2R = math::Vec2<Real>;
using Vec2I = math::Vec2<Index32>;
using Vec2f = math::Vec2<float>;
using Vec2H = math::Vec2<math::half>;
using math::Vec2i;
using math::Vec2s;
using math::Vec2d;

// Three-dimensional vector types
using Vec3R = math::Vec3<Real>;
using Vec3I = math::Vec3<Index32>;
using Vec3f = math::Vec3<float>;
using Vec3H = math::Vec3<math::half>;
using Vec3U8 = math::Vec3<uint8_t>;
using Vec3U16 = math::Vec3<uint16_t>;
using math::Vec3i;
using math::Vec3s;
using math::Vec3d;

using math::Coord;
using math::CoordBBox;
using BBoxd = math::BBox<Vec3d>;

// Four-dimensional vector types
using Vec4R = math::Vec4<Real>;
using Vec4I = math::Vec4<Index32>;
using Vec4f = math::Vec4<float>;
using Vec4H = math::Vec4<math::half>;
using math::Vec4i;
using math::Vec4s;
using math::Vec4d;

// Three-dimensional matrix types
using Mat3R = math::Mat3<Real>;
using math::Mat3s;
using math::Mat3d;

// Four-dimensional matrix types
using Mat4R = math::Mat4<Real>;
using math::Mat4s;
using math::Mat4d;

// Quaternions
using QuatR = math::Quat<Real>;
using math::Quats;
using math::Quatd;

// Dummy type for a voxel with a binary mask value, e.g. the active state
class ValueMask {};

// Use STL shared pointers from OpenVDB 4 on.
template<typename T> using SharedPtr = std::shared_ptr<T>;
template<typename T> using WeakPtr = std::weak_ptr<T>;

/// @brief Return a new shared pointer that points to the same object
/// as the given pointer but with possibly different <TT>const</TT>-ness.
/// @par Example:
/// @code
/// FloatGrid::ConstPtr grid = ...;
/// FloatGrid::Ptr nonConstGrid = ConstPtrCast<FloatGrid>(grid);
/// FloatGrid::ConstPtr constGrid = ConstPtrCast<const FloatGrid>(nonConstGrid);
/// @endcode
template<typename T, typename U> inline SharedPtr<T>
ConstPtrCast(const SharedPtr<U>& ptr) { return std::const_pointer_cast<T, U>(ptr); }

/// @brief Return a new shared pointer that is either null or points to
/// the same object as the given pointer after a @c dynamic_cast.
/// @par Example:
/// @code
/// GridBase::ConstPtr grid = ...;
/// FloatGrid::ConstPtr floatGrid = DynamicPtrCast<const FloatGrid>(grid);
/// @endcode
template<typename T, typename U> inline SharedPtr<T>
DynamicPtrCast(const SharedPtr<U>& ptr) { return std::dynamic_pointer_cast<T, U>(ptr); }

/// @brief Return a new shared pointer that points to the same object
/// as the given pointer after a @c static_cast.
/// @par Example:
/// @code
/// FloatGrid::Ptr floatGrid = ...;
/// GridBase::Ptr grid = StaticPtrCast<GridBase>(floatGrid);
/// @endcode
template<typename T, typename U> inline SharedPtr<T>
StaticPtrCast(const SharedPtr<U>& ptr) { return std::static_pointer_cast<T, U>(ptr); }


////////////////////////////////////////


/// @brief  Integer wrapper, required to distinguish PointIndexGrid and
///         PointDataGrid from Int32Grid and Int64Grid
/// @note   @c Kind is a dummy parameter used to create distinct types.
template<typename IntType_, Index Kind>
struct PointIndex
{
    static_assert(std::is_integral<IntType_>::value, "PointIndex requires an integer value type");

    using IntType = IntType_;

    PointIndex(IntType i = IntType(0)): mIndex(i) {}

    /// Explicit type conversion constructor
    template<typename T> explicit PointIndex(T i): mIndex(static_cast<IntType>(i)) {}

    operator IntType() const { return mIndex; }

    /// Needed to support the <tt>(zeroVal<PointIndex>() + val)</tt> idiom.
    template<typename T>
    PointIndex operator+(T x) { return PointIndex(mIndex + IntType(x)); }

private:
    IntType mIndex;
};


using PointIndex32 = PointIndex<Index32, 0>;
using PointIndex64 = PointIndex<Index64, 0>;

using PointDataIndex32 = PointIndex<Index32, 1>;
using PointDataIndex64 = PointIndex<Index64, 1>;


////////////////////////////////////////


/// @brief Helper metafunction used to determine if the first template
/// parameter is a specialization of the class template given in the second
/// template parameter
template <typename T, template <typename...> class Template>
struct IsSpecializationOf: public std::false_type {};

template <typename... Args, template <typename...> class Template>
struct IsSpecializationOf<Template<Args...>, Template>: public std::true_type {};


////////////////////////////////////////


/// @brief  Re-implementation of C++17's index_sequence and the helper alias
///   make_index_sequence. This was introduced to fix an issue with clang's
///   builtin implementation which treats template specializations of builtin
///   templates differently when a subsequent parameter is dependent. The
///   result is a resolution failure during partial specialization selection.
///   For example, the following will fail to specialize:
///
/// @code
///    struct Test { static const int VALUE = 1; };
///
///    template <typename T, typename S = std::make_index_sequence<T::VALUE>>
///    struct Item {};
///    template <typename T> struct Adapter {};
///    template <typename T> struct Adapter<Item<T>> {};  // FAIL: will never be selected.
/// @endcode
///
///  This is fixed from Clang16. See also:
///    https://reviews.llvm.org/D133262
///    https://github.com/llvm/llvm-project/issues/42102
///    https://github.com/llvm/llvm-project/issues/51928
///    https://github.com/llvm/llvm-project/commit/f4ea3bd4b2086e6de10131b197aaf7d066a24df8
template <std::size_t... Ns>
struct index_sequence {};

template <std::size_t N, std::size_t... Is>
auto make_index_sequence_impl() {
    // only one branch is considered. The other may be ill-formed
    if constexpr (N == 0) return index_sequence<Is...>(); // end case
    else return make_index_sequence_impl<N-1, N-1, Is...>(); // recursion
}

template <std::size_t N>
using make_index_sequence =
    std::decay_t<decltype(make_index_sequence_impl<N>())>;


////////////////////////////////////////


template<typename T, bool = IsSpecializationOf<T, math::Vec2>::value ||
                            IsSpecializationOf<T, math::Vec3>::value ||
                            IsSpecializationOf<T, math::Vec4>::value>
struct VecTraits
{
    static const bool IsVec = true;
    static const int Size = T::size;
    using ElementType = typename T::ValueType;
};

template<typename T>
struct VecTraits<T, false>
{
    static const bool IsVec = false;
    static const int Size = 1;
    using ElementType = T;
};

template<typename T, bool = IsSpecializationOf<T, math::Quat>::value>
struct QuatTraits
{
    static const bool IsQuat = true;
    static const int Size = T::size;
    using ElementType = typename T::ValueType;
};

template<typename T>
struct QuatTraits<T, false>
{
    static const bool IsQuat = false;
    static const int Size = 1;
    using ElementType = T;
};

template<typename T, bool = IsSpecializationOf<T, math::Mat3>::value ||
                            IsSpecializationOf<T, math::Mat4>::value>
struct MatTraits
{
    static const bool IsMat = true;
    static const int Size = T::size;
    using ElementType = typename T::ValueType;
};

template<typename T>
struct MatTraits<T, false>
{
    static const bool IsMat = false;
    static const int Size = 1;
    using ElementType = T;
};

template<typename T, bool = VecTraits<T>::IsVec ||
                            QuatTraits<T>::IsQuat ||
                            MatTraits<T>::IsMat>
struct ValueTraits
{
    static const bool IsVec = VecTraits<T>::IsVec;
    static const bool IsQuat = QuatTraits<T>::IsQuat;
    static const bool IsMat = MatTraits<T>::IsMat;
    static const bool IsScalar = false;
    static const int Size = T::size;
    static const int Elements = IsMat ? Size*Size : Size;
    using ElementType = typename T::ValueType;
};

template<typename T>
struct ValueTraits<T, false>
{
    static const bool IsVec = false;
    static const bool IsQuat = false;
    static const bool IsMat = false;
    static const bool IsScalar = true;
    static const int Size = 1;
    static const int Elements = 1;
    using ElementType = T;
};


/// @brief Conversion classes for changing the underlying type of VDB types
/// @{
template<typename T, typename SubT> struct ConvertElementType { using Type = SubT; };
template<typename T, typename SubT> struct ConvertElementType<math::Vec2<T>, SubT> { using Type = math::Vec2<SubT>; };
template<typename T, typename SubT> struct ConvertElementType<math::Vec3<T>, SubT> { using Type = math::Vec3<SubT>; };
template<typename T, typename SubT> struct ConvertElementType<math::Vec4<T>, SubT> { using Type = math::Vec4<SubT>; };
template<typename T, typename SubT> struct ConvertElementType<math::Quat<T>, SubT> { using Type = math::Quat<SubT>; };
template<typename T, typename SubT> struct ConvertElementType<math::Mat3<T>, SubT> { using Type = math::Mat3<SubT>; };
template<typename T, typename SubT> struct ConvertElementType<math::Mat4<T>, SubT> { using Type = math::Mat4<SubT>; };
/// @}

namespace types_internal
{
template <size_t Bits, bool Signed> struct int_t;
template <> struct int_t<8ul, true>   { using type = int8_t;   };
template <> struct int_t<16ul, true>  { using type = int16_t;  };
template <> struct int_t<32ul, true>  { using type = int32_t;  };
template <> struct int_t<64ul, true>  { using type = int64_t;  };
template <> struct int_t<8ul, false>  { using type = uint8_t;  };
template <> struct int_t<16ul, false> { using type = uint16_t; };
template <> struct int_t<32ul, false> { using type = uint32_t; };
template <> struct int_t<64ul, false> { using type = uint64_t; };

template <size_t Bits> struct flt_t;
template <> struct flt_t<16ul> { using type = math::half; };
template <> struct flt_t<32ul> { using type = float; };
template <> struct flt_t<64ul> { using type = double; };
}

/// @brief Promotion classes which provide an interface for elevating and
///   demoting a scalar or VDB type to a higher or lower precision. Integer
///   types preserve their sign. Types promotion are only valid between
///   8 to 64 bits (long doubles are not supported).
/// @{
template<typename T>
struct PromoteType
{
private:
    template <size_t bits>
    using TypeT = typename std::conditional<std::is_integral<T>::value,
        types_internal::int_t<bits, std::is_signed<T>::value>,
        types_internal::flt_t<std::max(size_t(16), bits)>>::type;
public:
    static_assert(sizeof(T) <= 8ul, "Unsupported source type for promotion");

#define OPENVDB_TARGET_BITS(SHIFT, PROMOTE) \
        std::max(size_t(8), \
            std::min(size_t(64), (PROMOTE ? size_t(8)*(sizeof(T)<<SHIFT) : \
                size_t(8)*(sizeof(T)>>SHIFT))))
    template <size_t Shift = ~0UL> using Promote = typename TypeT<OPENVDB_TARGET_BITS(Shift, true)>::type;
    template <size_t Shift = ~0UL> using Demote = typename TypeT<OPENVDB_TARGET_BITS(Shift, false)>::type;
#undef OPENVDB_TARGET_BITS

    using Highest = typename TypeT<64ul>::type;
    using Lowest = typename TypeT<8ul>::type;
    using Next = Promote<1>;
    using Previous = Demote<1>;
};

template <typename T, template <typename> class ContainerT>
struct PromoteContainerType
{
    template <size_t Shift = ~0UL> using Promote = ContainerT<typename PromoteType<T>::template Promote<Shift>>;
    template <size_t Shift = ~0UL> using Demote = ContainerT<typename PromoteType<T>::template Demote<Shift>>;
    using Highest = ContainerT<typename PromoteType<T>::Highest>;
    using Lowest = ContainerT<typename PromoteType<T>::Lowest>;
    using Next = ContainerT<typename PromoteType<T>::Next>;
    using Previous = ContainerT<typename PromoteType<T>::Previous>;
};

template<typename T> struct PromoteType<math::Vec2<T>> : public PromoteContainerType<T, math::Vec2> {};
template<typename T> struct PromoteType<math::Vec3<T>> : public PromoteContainerType<T, math::Vec3> {};
template<typename T> struct PromoteType<math::Vec4<T>> : public PromoteContainerType<T, math::Vec4> {};
template<typename T> struct PromoteType<math::Quat<T>> : public PromoteContainerType<T, math::Quat> {};
template<typename T> struct PromoteType<math::Mat3<T>> : public PromoteContainerType<T, math::Mat3> {};
template<typename T> struct PromoteType<math::Mat4<T>> : public PromoteContainerType<T, math::Mat4> {};
/// @}


////////////////////////////////////////


/// @brief CanConvertType<FromType, ToType>::value is @c true if a value
/// of type @a ToType can be constructed from a value of type @a FromType.
template<typename FromType, typename ToType>
struct CanConvertType { enum { value = std::is_constructible<ToType, FromType>::value }; };

// Specializations for vector types, which can be constructed from values
// of their own ValueTypes (or values that can be converted to their ValueTypes),
// but only explicitly
template<typename T> struct CanConvertType<T, math::Vec2<T> > { enum { value = true }; };
template<typename T> struct CanConvertType<T, math::Vec3<T> > { enum { value = true }; };
template<typename T> struct CanConvertType<T, math::Vec4<T> > { enum { value = true }; };
template<typename T> struct CanConvertType<math::Vec2<T>, math::Vec2<T> > { enum {value = true}; };
template<typename T> struct CanConvertType<math::Vec3<T>, math::Vec3<T> > { enum {value = true}; };
template<typename T> struct CanConvertType<math::Vec4<T>, math::Vec4<T> > { enum {value = true}; };
template<typename T0, typename T1>
struct CanConvertType<T0, math::Vec2<T1> > { enum { value = CanConvertType<T0, T1>::value }; };
template<typename T0, typename T1>
struct CanConvertType<T0, math::Vec3<T1> > { enum { value = CanConvertType<T0, T1>::value }; };
template<typename T0, typename T1>
struct CanConvertType<T0, math::Vec4<T1> > { enum { value = CanConvertType<T0, T1>::value }; };
template<> struct CanConvertType<PointIndex32, PointDataIndex32> { enum {value = true}; };
template<> struct CanConvertType<PointDataIndex32, PointIndex32> { enum {value = true}; };
template<typename T>
struct CanConvertType<T, ValueMask> { enum {value = CanConvertType<T, bool>::value}; };
template<typename T>
struct CanConvertType<ValueMask, T> { enum {value = CanConvertType<bool, T>::value}; };


////////////////////////////////////////


/// @brief CopyConstness<T1, T2>::Type is either <tt>const T2</tt>
/// or @c T2 with no @c const qualifier, depending on whether @c T1 is @c const.
/// @details For example,
/// - CopyConstness<int, int>::Type is @c int
/// - CopyConstness<int, const int>::Type is @c int
/// - CopyConstness<const int, int>::Type is <tt>const int</tt>
/// - CopyConstness<const int, const int>::Type is <tt>const int</tt>
template<typename FromType, typename ToType> struct CopyConstness {
    using Type = typename std::remove_const<ToType>::type;
};

/// @cond OPENVDB_DOCS_INTERNAL
template<typename FromType, typename ToType> struct CopyConstness<const FromType, ToType> {
    using Type = const ToType;
};
/// @endcond


////////////////////////////////////////


// Add new items to the *end* of this list, and update NUM_GRID_CLASSES.
enum GridClass {
    GRID_UNKNOWN = 0,
    GRID_LEVEL_SET,
    GRID_FOG_VOLUME,
    GRID_STAGGERED
};
enum { NUM_GRID_CLASSES = GRID_STAGGERED + 1 };

static const Real LEVEL_SET_HALF_WIDTH = 3;

/// The type of a vector determines how transforms are applied to it:
/// <dl>
/// <dt><b>Invariant</b>
/// <dd>Does not transform (e.g., tuple, uvw, color)
///
/// <dt><b>Covariant</b>
/// <dd>Apply inverse-transpose transformation: @e w = 0, ignores translation
///     (e.g., gradient/normal)
///
/// <dt><b>Covariant Normalize</b>
/// <dd>Apply inverse-transpose transformation: @e w = 0, ignores translation,
///     vectors are renormalized (e.g., unit normal)
///
/// <dt><b>Contravariant Relative</b>
/// <dd>Apply "regular" transformation: @e w = 0, ignores translation
///     (e.g., displacement, velocity, acceleration)
///
/// <dt><b>Contravariant Absolute</b>
/// <dd>Apply "regular" transformation: @e w = 1, vector translates (e.g., position)
/// </dl>
enum VecType {
    VEC_INVARIANT = 0,
    VEC_COVARIANT,
    VEC_COVARIANT_NORMALIZE,
    VEC_CONTRAVARIANT_RELATIVE,
    VEC_CONTRAVARIANT_ABSOLUTE
};
enum { NUM_VEC_TYPES = VEC_CONTRAVARIANT_ABSOLUTE + 1 };


/// Specify how grids should be merged during certain (typically multithreaded) operations.
/// <dl>
/// <dt><b>MERGE_ACTIVE_STATES</b>
/// <dd>The output grid is active wherever any of the input grids is active.
///
/// <dt><b>MERGE_NODES</b>
/// <dd>The output grid's tree has a node wherever any of the input grids' trees
///     has a node, regardless of any active states.
///
/// <dt><b>MERGE_ACTIVE_STATES_AND_NODES</b>
/// <dd>The output grid is active wherever any of the input grids is active,
///     and its tree has a node wherever any of the input grids' trees has a node.
/// </dl>
enum MergePolicy {
    MERGE_ACTIVE_STATES = 0,
    MERGE_NODES,
    MERGE_ACTIVE_STATES_AND_NODES
};


////////////////////////////////////////


template<typename T> const char* typeNameAsString()                 { return typeid(T).name(); }
template<> inline const char* typeNameAsString<bool>()              { return "bool"; }
template<> inline const char* typeNameAsString<ValueMask>()         { return "mask"; }
template<> inline const char* typeNameAsString<math::half>()              { return "half"; }
template<> inline const char* typeNameAsString<float>()             { return "float"; }
template<> inline const char* typeNameAsString<double>()            { return "double"; }
template<> inline const char* typeNameAsString<int8_t>()            { return "int8"; }
template<> inline const char* typeNameAsString<uint8_t>()           { return "uint8"; }
template<> inline const char* typeNameAsString<int16_t>()           { return "int16"; }
template<> inline const char* typeNameAsString<uint16_t>()          { return "uint16"; }
template<> inline const char* typeNameAsString<int32_t>()           { return "int32"; }
template<> inline const char* typeNameAsString<uint32_t>()          { return "uint32"; }
template<> inline const char* typeNameAsString<int64_t>()           { return "int64"; }
template<> inline const char* typeNameAsString<Vec2i>()             { return "vec2i"; }
template<> inline const char* typeNameAsString<Vec2s>()             { return "vec2s"; }
template<> inline const char* typeNameAsString<Vec2d>()             { return "vec2d"; }
template<> inline const char* typeNameAsString<Vec3U8>()            { return "vec3u8"; }
template<> inline const char* typeNameAsString<Vec3U16>()           { return "vec3u16"; }
template<> inline const char* typeNameAsString<Vec3i>()             { return "vec3i"; }
template<> inline const char* typeNameAsString<Vec3f>()             { return "vec3s"; }
template<> inline const char* typeNameAsString<Vec3d>()             { return "vec3d"; }
template<> inline const char* typeNameAsString<Vec4i>()             { return "vec4i"; }
template<> inline const char* typeNameAsString<Vec4f>()             { return "vec4s"; }
template<> inline const char* typeNameAsString<Vec4d>()             { return "vec4d"; }
template<> inline const char* typeNameAsString<std::string>()       { return "string"; }
template<> inline const char* typeNameAsString<Mat3s>()             { return "mat3s"; }
template<> inline const char* typeNameAsString<Mat3d>()             { return "mat3d"; }
template<> inline const char* typeNameAsString<Mat4s>()             { return "mat4s"; }
template<> inline const char* typeNameAsString<Mat4d>()             { return "mat4d"; }
template<> inline const char* typeNameAsString<math::Quats>()       { return "quats"; }
template<> inline const char* typeNameAsString<math::Quatd>()       { return "quatd"; }
template<> inline const char* typeNameAsString<PointIndex32>()      { return "ptidx32"; }
template<> inline const char* typeNameAsString<PointIndex64>()      { return "ptidx64"; }
template<> inline const char* typeNameAsString<PointDataIndex32>()  { return "ptdataidx32"; }
template<> inline const char* typeNameAsString<PointDataIndex64>()  { return "ptdataidx64"; }


////////////////////////////////////////


/// @brief This struct collects both input and output arguments to "grid combiner" functors
/// used with the tree::TypedGrid::combineExtended() and combine2Extended() methods.
/// AValueType and BValueType are the value types of the two grids being combined.
///
/// @see openvdb/tree/Tree.h for usage information.
///
/// Setter methods return references to this object, to facilitate the following usage:
/// @code
///     CombineArgs<float> args;
///     myCombineOp(args.setARef(aVal).setBRef(bVal).setAIsActive(true).setBIsActive(false));
/// @endcode
template<typename AValueType, typename BValueType = AValueType>
class CombineArgs
{
public:
    using AValueT = AValueType;
    using BValueT = BValueType;

    CombineArgs()
        : mAValPtr(nullptr)
        , mBValPtr(nullptr)
        , mResultValPtr(&mResultVal)
        , mAIsActive(false)
        , mBIsActive(false)
        , mResultIsActive(false)
    {
    }

    /// Use this constructor when the result value is stored externally.
    CombineArgs(const AValueType& a, const BValueType& b, AValueType& result,
                bool aOn = false, bool bOn = false)
        : mAValPtr(&a)
        , mBValPtr(&b)
        , mResultValPtr(&result)
        , mAIsActive(aOn)
        , mBIsActive(bOn)
    {
        this->updateResultActive();
    }

    /// Use this constructor when the result value should be stored in this struct.
    CombineArgs(const AValueType& a, const BValueType& b, bool aOn = false, bool bOn = false)
        : mAValPtr(&a)
        , mBValPtr(&b)
        , mResultValPtr(&mResultVal)
        , mAIsActive(aOn)
        , mBIsActive(bOn)
    {
        this->updateResultActive();
    }

    /// Get the A input value.
    const AValueType& a() const { return *mAValPtr; }
    /// Get the B input value.
    const BValueType& b() const { return *mBValPtr; }
    //@{
    /// Get the output value.
    const AValueType& result() const { return *mResultValPtr; }
    AValueType& result() { return *mResultValPtr; }
    //@}

    /// Set the output value.
    CombineArgs& setResult(const AValueType& val) { *mResultValPtr = val; return *this; }

    /// Redirect the A value to a new external source.
    CombineArgs& setARef(const AValueType& a) { mAValPtr = &a; return *this; }
    /// Redirect the B value to a new external source.
    CombineArgs& setBRef(const BValueType& b) { mBValPtr = &b; return *this; }
    /// Redirect the result value to a new external destination.
    CombineArgs& setResultRef(AValueType& val) { mResultValPtr = &val; return *this; }

    /// @return true if the A value is active
    bool aIsActive() const { return mAIsActive; }
    /// @return true if the B value is active
    bool bIsActive() const { return mBIsActive; }
    /// @return true if the output value is active
    bool resultIsActive() const { return mResultIsActive; }

    /// Set the active state of the A value.
    CombineArgs& setAIsActive(bool b) { mAIsActive = b; updateResultActive(); return *this; }
    /// Set the active state of the B value.
    CombineArgs& setBIsActive(bool b) { mBIsActive = b; updateResultActive(); return *this; }
    /// Set the active state of the output value.
    CombineArgs& setResultIsActive(bool b) { mResultIsActive = b; return *this; }

protected:
    /// By default, the result value is active if either of the input values is active,
    /// but this behavior can be overridden by calling setResultIsActive().
    void updateResultActive() { mResultIsActive = mAIsActive || mBIsActive; }

    const AValueType* mAValPtr;   // pointer to input value from A grid
    const BValueType* mBValPtr;   // pointer to input value from B grid
    AValueType mResultVal;        // computed output value (unused if stored externally)
    AValueType* mResultValPtr;    // pointer to either mResultVal or an external value
    bool mAIsActive, mBIsActive;  // active states of A and B values
    bool mResultIsActive;         // computed active state (default: A active || B active)
};


/// This struct adapts a "grid combiner" functor to swap the A and B grid values
/// (e.g., so that if the original functor computes a + 2 * b, the adapted functor
/// will compute b + 2 * a).
template<typename ValueType, typename CombineOp>
struct SwappedCombineOp
{
    SwappedCombineOp(CombineOp& _op): op(_op) {}

    void operator()(CombineArgs<ValueType>& args)
    {
        CombineArgs<ValueType> swappedArgs(args.b(), args.a(), args.result(),
            args.bIsActive(), args.aIsActive());
        op(swappedArgs);
        args.setResultIsActive(swappedArgs.resultIsActive());
    }

    CombineOp& op;
};


////////////////////////////////////////


/// @brief Tag dispatch class that distinguishes shallow copy constructors
/// from deep copy constructors
class ShallowCopy {};
/// @brief Tag dispatch class that distinguishes topology copy constructors
/// from deep copy constructors
class TopologyCopy {};
/// @brief Tag dispatch class that distinguishes constructors that deep copy
class DeepCopy {};
/// @brief Tag dispatch class that distinguishes constructors that steal
class Steal {};
/// @brief Tag dispatch class that distinguishes constructors during file input
class PartialCreate {};

} // namespace OPENVDB_VERSION_NAME
} // namespace openvdb


#endif // OPENVDB_TYPES_HAS_BEEN_INCLUDED