/**

@page changes Release Notes


@htmlonly <a name="v3_1_0_changes"></a>@endhtmlonly
@par
<B>Version 3.1.0</B> - <I>October 1, 2015</I>

@par
Highlights:
- New features: advection of arbitrary volumes, general-purpose
  preconditioned linear solver and Poisson solver, segmentation
  of topologically-enclosed regions of a volume, new and faster bitmask
  operators, concurrent paged array, volume diagnostics
- Optimizations: threaded grid constructors and topology operations;
  faster mesh to volume conversion, SDF to fog volume conversion
  and grid pruning; faster, unbounded particle partitioning
- New Houdini nodes: Advect, Diagnostics, Rasterize Points, Remap,
  Remove Divergence, Sort Points

@par
New features:
- Added a @vdblink::tools::VolumeAdvection volume advection@endlink tool
  for sparse advection of non-level-set volumes.
- Added a preconditioned
  @vdblink::math::pcg::solve() conjugate gradient solver@endlink.
- Added a @vdblink::tools::poisson::solve() Poisson solver@endlink
  for functions sampled on grids.
- Added @vdblink::tools::extractEnclosedRegion extractEnclosedRegion@endlink,
  which detects topologically-enclosed (watertight) exterior regions (cavities)
  that can result from CSG union operations between level sets with concavities
  that are capped.
  (See the unit test @c TestPoissonSolver::testSolveWithSegmentDomain
  for an example in which this tool is used to identify regions of trapped
  fluid when solving for pressure in a volume of incompressible fluid.)
- Added @vdblink::util::PagedArray PagedArray@endlink, a concurrent,
  dynamic linear array data structure with fast <I>O</I>(1) value access
  (both random and sequential).
- Added @vdblink::tools::Sampler Sampler@endlink, which provides a unified API
  for both staggered and non-staggered interpolation of various orders.
- Added equality and inequality operators to
  @vdblink::Metadata Metadata@endlink and @vdblink::MetaMap MetaMap@endlink.
- Added @vdblink::tools::CheckLevelSet CheckLevelSet@endlink and
  @vdblink::tools::CheckFogVolume CheckFogVolume@endlink tools that
  perform various tests on symmetric, narrow-band level sets and fog volumes,
  respectively, to diagnose potential issues.
- Added support for value accessors that are not registered with their trees.
  (Bypassing accessor registration can improve performance in rare cases
  but should be used with caution, since the accessor will be left in an
  invalid state if the tree topology is modified.)
- Added a @vdblink::tree::Tree::stealNodes() stealNodes@endlink method that
  transfers ownership of all nodes in a tree of a certain type and inserts
  them into a linear array.
- Added a @vdblink::tools::createLevelSetBox() tools::createLevelSetBox@endlink
  factory function for level-set grids.
- Added @vdblink::tools::Dense::offsetToCoord() Dense::offsetToCoord@endlink.
- Added @vdblink::tree::LeafNode::Buffer::data() LeafNode::Buffer::data@endlink,
  which provides direct access to a leaf node&rsquo;s voxel value array,
  avoiding out-of-core overhead.  Use with caution.
- Added a @vdblink::util::NodeMask::foreach() NodeMask::foreach@endlink method
  for efficient evaluation of complex bitwise operations.
- Added a bitwise difference method to
  @vdblink::util::NodeMask::operator-=() NodeMask@endlink.
- Added a @c -version option to @c vdb_print, @c vdb_render and @c vdb_view.

@par
Improvements:
- Deep, conversion and topology copy @vdblink::Grid Grid@endlink constructors
  are now threaded and up to five times faster.
- @vdblink::Grid::topologyUnion() Grid::topologyUnion@endlink,
  @vdblink::Grid::topologyIntersection() Grid::topologyIntersection@endlink, and
  @vdblink::Grid::topologyDifference() Grid::topologyDifference@endlink are now
  much faster due to threading.
- Significantly improved the performance, parallel scaling and memory usage
  of the @vdblink::tools::meshToVolume() mesh to volume@endlink converter,
  and implemented a more robust inside/outside sign classification scheme.
- Reimplemented the
  @vdblink::tools::PointPartitioner point partitioning@endlink
  tool for improved performance, concurrency and memory usage.
  The tool is now unbounded in the sense that points may be distributed
  anywhere in index space.
- Significantly improved the performance of the
  @vdblink::tools::sdfToFogVolume() SDF to fog volume@endlink converter.
- Significantly improved the performance of the
  @vdblink::tools::sdfInteriorMask() sdfInteriorMask@endlink tool
  and added support for both grid and tree inputs.
- Made various optimizations and improvements to the
  @vdblink::tools::LevelSetMorphing level set morphing@endlink tool.
- Aggregated @vdblink::tools::DiscreteField DiscreteField@endlink and
  @vdblink::tools::EnrightField EnrightField@endlink (formerly in
  tools/LevelSetAdvect.h) and
  @vdblink::tools::VelocitySampler VelocitySampler@endlink and
  @vdblink::tools::VelocityIntegrator VelocityIntegrator@endlink (formerly
  in tools/PointAdvect.h) into a single header, tools/VelocityFields.h.
- Modified the @vdblink::tools::signedFloodFill() signed flood fill@endlink
  tool to accept grids of any signed scalar value type, not just
  floating-point grids.
- The @vdblink::tools::prune() prune@endlink tool is now faster, and it employs
  an improved compression technique on trees with floating-point values.

@par
Bug fixes:
- Fixed a build issue that could result in spurious &ldquo;Blosc encoding
  is not supported&rdquo; errors unless @c OPENVDB_USE_BLOSC was
  <TT>@#define</TT>d when compiling client code.
- Added NaN and inf checks to the
  @vdblink::tools::PointPartitioner point partitioning@endlink tool.
- Fixed a <TT>vdb_view</TT> issue whereby the frame buffer size did not
  necessarily match the window size.
  <I>[Contributed by Rafael&nbsp;Campos]</I>
- Fixed a roundoff issue in
  @vdblink::tools::LevelSetTracker LevelSetTracker@endlink
  that could result in NaNs.
- Changed @vdblink::tools::CheckNormGrad CheckNormGrad@endlink to check
  the magnitude of the gradient rather than the square of the magnitude.
- Fixed parameter type inconsistencies in math/Ray.h and
  tools/RayIntersector.h.
  <I>[Contributed by K&eacute;vin&nbsp;Dietrich]</I>
- Fixed incorrect handling of signed values in the
  @vdblink::tools::clip() clip@endlink tool (and the Clip SOP).

@par
API changes:
- Removed the <TT>math::Hermite</TT> class since it was no longer used
  and caused build issues for some.
- Refactored the @vdblink::tools::LevelSetAdvection level set advection@endlink,
  @vdblink::tools::LevelSetFilter level set filtering@endlink,
  @vdblink::tools::LevelSetMeasure level set measuring@endlink
  and @vdblink::tools::LevelSetTracker level set tracking@endlink tools.
- Extended the API of the @vdblink::tools::Diagnose Diagnose@endlink tool
  and disabled copy construction.
- Extended and unified the API of various Samplers.
- Added an optional template argument to the
  @vdblink::tree::ValueAccessor ValueAccessor@endlink class
  to allow for unregistered accessors.

@par
Houdini:
- Added a Rasterize Points SOP that produces density volumes and transfers
  arbitrary point attributes using a weighted-average scheme.
  The node incorporates a VOP subnetwork for procedural modeling,
  and its accompanying creation script defines a default network with
  VEX procedures for cloud and velocity field modeling.
  (See the creation script file header for installation details.)
- Merged the Advect Level Set SOP into a new Advect SOP that supports
  advection of arbitrary volumes, not just level sets.
- Added a Remove Divergence SOP that eliminates divergence from a
  velocity field.
- Added a Diagnostics SOP that can identify various problems with
  level sets, fog volumes and other grids.
- Added a Sort Points SOP that spatially reorders a list of points
  so that points that are close together in space are also close together
  in the list.
  This can improve CPU cache coherency and performance for
  random-access operations.
- Added a Remap SOP that maps voxel values in an input range to values
  in an output range through a user-defined transfer function.
- Added an option to the Convert SOP to activate interior voxels.
  <I>[Contributed by SESI]</I>
- The To Spheres SOP can now optionally output a <TT>pscale</TT> attribute.
- Added <TT>openvdb_houdini::SOP_NodeVDB::duplicateSourceStealable()</TT>,
  which in conjunction with the Unload flag can help to minimize deep copying
  of grids between nodes.
  The Advect, Convert, Fill, Filter, Fracture, Noise, Offset Level Set,
  Prune, Remap, Remove Divergence, Renormalize Level Set, Resize Narrow Band,
  Smooth Level Set and Transform SOPs all have this optimization enabled,
  meaning that they can potentially steal, rather than copy, data from
  upstream nodes that have the Unload flag enabled.
  <I>[Contributed by Double&nbsp;Negative]</I>
- Redesigned the UI of the Visualize SOP and added toggles to draw with
  or without color, to use the grid name as the attribute name for points
  with values, and to attach grid index coordinates to points.
- Added toggles to the Filter, Rebuild Level Set, Resize Narrow Band,
  Smooth Level Set and To Spheres SOPs to specify units in either
  world space or index space.
- Fixed an issue whereby grids generated by the Rebuild Level Set SOP
  did not always display as surfaces in the viewport.
- The Metadata SOP now sets appropriate viewport visualization options
  when the grid class is changed.

@htmlonly <a name="v3_0_0_changes"></a>@endhtmlonly
@par
<B>Version 3.0.0</B> - <I>January 14, 2015</I>
- The @vdblink::io::File File@endlink class now supports delayed loading of
  <TT>.vdb</TT> files, meaning that memory is not allocated for voxel values
  until the values are actually accessed. (This feature is enabled by default.)
  Until a grid has been fully loaded, its source <TT>.vdb</TT> file must not be
  modified or deleted, so for safety,
  @vdblink::io::File::open() File::open@endlink automatically makes
  private copies of source files that are smaller than a user-specified limit
  (see @vdblink::io::File::setCopyMaxBytes() File::setCopyMaxBytes@endlink).
  The limit can be set to zero to disable copying, but if it cannot be
  guaranteed that a file will not be modified, then it is best not to enable
  delayed loading for that file.
- <TT>.vdb</TT> files can now optionally be compressed with the Blosc&nbsp;LZ4
  codec.  <A HREF="http://www.blosc.org/">Blosc</A> compresses almost as well
  as ZLIB, but it is much faster.
- Added @vdblink::tools::PointPartitioner PointPartitioner@endlink, a tool
  for fast spatial sorting of points stored in an external array, and
  @link PointIndexGrid.h PointIndexGrid@endlink, an acceleration structure
  for fast range and nearest-neighbor searches.
- Added @link NodeManager.h tree::NodeManager@endlink,
  which linearizes a tree to facilitate efficient multithreading
  across all tree levels.
- Added @vdblink::tools::prune() tools::prune@endlink (and other variants),
  which replaces and outperforms @c Tree::prune.
- Added @vdblink::tools::signedFloodFill() tools::signedFloodFill@endlink,
  which replaces and outperforms @c Tree::signedFloodFill.
- Added @vdblink::tools::changeBackground() tools::changeBackground@endlink
  (and other variants), which replaces and outperforms @c Tree::setBackground().
- Added a fast but approximate narrow-band level set
  @vdblink::tools::LevelSetTracker::dilate() dilation@endlink method, a fast
  narrow-band level set
  @vdblink::tools::LevelSetTracker::erode() erosion@endlink
  method, and a @vdblink::tools::LevelSetTracker::normalize(const MaskType*)
  masked normalization@endlink method to
  @vdblink::tools::LevelSetTracker LevelSetTracker@endlink.
- Added @vdblink::tools::Diagnose Diagnose@endlink, which performs
  multithreaded diagnostics on grids to identify issues like values that
  are NaNs or out-of-range. It optionally generates a boolean grid of all
  values that fail user-defined tests.
- Added optional alpha masks to @vdblink::tools::LevelSetMorphing
  LevelSetMorphing@endlink.
- Fixed an intermittent crash in
  @vdblink::tools::LevelSetMorphing LevelSetMorphing@endlink.
- Added @c tools::topologyToLevelSet(),
  which generates a level set from the implicit boundary between active
  and inactive voxels in an arbitrary input grid.
  <I>[DWA internal]</I>
- Improved the performance of point scattering (by orders of magnitude)
  and added a
  @vdblink::tools::DenseUniformPointScatter DenseUniformPointScatter@endlink
  class as well as support for fractional numbers of particles per voxel.
- Improved the performance and memory footprint of
  the @vdblink::tools::ParticlesToLevelSet ParticlesToLevelSet@endlink tool
  for large numbers (tens to hundreds of millions) of particles.
- Added edge-adjacent (6+12=18 neighbors) and vertex-adjacent (6+12+8=26
  neighbors) dilation algorithms to
  @vdblink::tools::Morphology::dilateVoxels Morphology::dilateVoxels@endlink.
  The default dilation pattern is still face-adjacent (6&nbsp;neighbors).
- Added @vdblink::tree::Tree::getNodes() Tree::getNodes@endlink, which allows
  for fast construction of linear arrays of tree nodes for use in multithreaded
  code such as the @vdblink::tree::LeafManager LeafManager@endlink or
  @link NodeManager.h tree::NodeManager@endlink.
- Added @vdblink::math::Extrema math::Extrema@endlink and
  @vdblink::tools::extrema() tools::extrema@endlink to efficiently
  compute minimum and maximum values in a grid.
- Added support for material color grids to all level set
  @vdblink::tools::BaseShader shaders@endlink, and added an option to
  @c vdb_render that allows one to specify a reference grid to be used
  for material color lookups.
- Added @vdblink::getLibraryVersionString()
  getLibraryVersionString@endlink and
  @link OPENVDB_LIBRARY_VERSION_STRING@endlink.
- Modified the mesh to volume converter to always set the grid background
  value to the exterior narrow-band width, and added finite value checks
  to narrow band parameters.
- @vdblink::tools::volumeToMesh() tools::volumeToMesh@endlink now compiles
  for all grid types but throws an exception if the input grid does not
  have a scalar value type.
- Added a
  @vdblink::io::File::readGrid(const Name&, const BBoxd&) File::readGrid@endlink
  overload and @vdblink::GridBase::readBuffers(std::istream&, const CoordBBox&)
  readBuffers@endlink overloads to the grid, tree and node classes that allow
  one to specify a bounding box against which to clip a grid while reading it.
  For large grids, clipping while reading can result in significantly lower
  memory usage than clipping after reading.
- Added @vdblink::GridBase::clipGrid() GridBase::clipGrid@endlink, which
  clips a grid against a world-space bounding box, and
  @vdblink::GridBase::clip() GridBase::clip@endlink and
  @vdblink::tree::Tree::clip() Tree::clip@endlink, which clip against
  an index-space bounding box.
- Added @vdblink::tools::clip() tools::clip@endlink, which clips a grid
  either against a bounding box or against the active voxels of a mask grid.
- @vdblink::io::File::readGridPartial() File::readGridPartial@endlink
  allocates the nodes of a grid&rsquo;s tree as before, but it now allocates
  leaf nodes without data buffers.  (This feature is mainly for internal use.
  Partially-read grids should be used with care if at all, and they should
  be treated as read-only.)
- Grid names retrieved using a
  @vdblink::io::File::NameIterator File::NameIterator@endlink now always
  uniquely identify grids; they no longer generate &lsquo;more than one grid
  named&nbsp;&ldquo;<I>x</I>&rdquo;&rsquo; warnings when there are multiple
  grids of the same name in a file (for files written starting with this
  version of the OpenVDB library).
- Fixed a bug in @vdblink::tree::Tree::ValueOffIter Tree::ValueOffIter@endlink
  that could cause
  @vdblink::tree::TreeValueIteratorBase::setMaxDepth() depth-bounded@endlink
  iterators to return incorrect values.
- Eliminated a recursive call in @vdblink::tree::TreeValueIteratorBase::next()
  TreeValueIteratorBase::next@endlink that could cause crashes on systems
  with a limited stack size.
- Fixed memory leaks in @vdblink::tree::RootNode::topologyDifference()
  RootNode::topologyDifference@endlink and
  @vdblink::tree::RootNode::topologyIntersection()
  RootNode::topologyIntersection@endlink.
- Fixed a memory leak in @vdblink::io::Queue io::Queue@endlink when the queue
  was full and a write task could not be added within the timeout interval.
- Fixed a potential division by zero crash in
  @vdblink::tools::compDiv() tools::compDiv@endlink with integer-valued grids.
- Fixed kernel normalization in the @vdblink::tools::Filter filter tool@endlink
  so that it is correct for integer-valued grids.
- Fixed a bug in @vdblink::tree::LeafNode::Buffer::getValue()
  LeafNode::Buffer::getValue@endlink whereby Visual C++ would return
  a reference to a temporary.
  <I>[Contributed by SESI]</I>
- Fixed a bug in @vdblink::tools::ParticlesToLevelSet
  tools::ParticlesToLevelSet@endlink related to attribute transfer
  when leaf nodes are produced without active values.
- Added @vdblink::util::CpuTimer util::CpuTimer@endlink and removed
  the more simplistic @c unittest_util::CpuTimer from @c unittest/util.h.
- Eliminated the use of @c getopt for command-line argument parsing
  in @c vdb_test.
- @vdblink::initialize() openvdb::initialize@endlink now properly initializes
  <A HREF="http://log4cplus.sourceforge.net/">log4cplus</A> if it is enabled,
  eliminating &ldquo;No appenders could be found&rdquo; errors.
- Fixed a bug in the
  @vdblink::math::QuantizedUnitVec::pack() QuantizedUnitVec::pack@endlink
  method that caused quantization artifacts.
- Added convenience class @vdblink::tools::AlphaMask AlphaMask@endlink
- Added constructors and methods to both
  @vdblink::math::RandInt RandInt@endlink and
  @vdblink::math::Rand01 Rand01@endlink to set and reset the random seed value.
- Added convenience methods for
  @vdblink::math::Transform::indexToWorld(const BBoxd&) const transforming@endlink
  @vdblink::math::Transform::worldToIndex(const BBoxd&) const bounding@endlink
  @vdblink::math::Transform::worldToIndexCellCentered(const BBoxd&) const boxes@endlink
  to @vdblink::math::Transform math::Transform@endlink.
- @c vdb_view is now compatible with both GLFW&nbsp;2 and GLFW&nbsp;3.
- Made many small changes to address type conversion and other warnings
  reported by newer compilers like GCC&nbsp;4.8 and ICC&nbsp;14.
- Replaced the @c HALF_INCL_DIR and @c HALF_LIB_DIR Makefile variables
  with @c ILMBASE_INCL_DIR and @c ILMBASE_LIB_DIR and added @c ILMBASE_LIB,
  to match <A HREF="https://github.com/openexr/openexr">OpenEXR</A>&rsquo;s
  library organization.  <I>[Contributed by Double&nbsp;Negative]</I>
- Eliminated most local (function-scope) static variables, because
  Visual&nbsp;C++ doesn&rsquo;t guarantee thread-safe initialization
  of local statics.  <I>[Contributed by&nbsp;SESI]</I>
- Fixed a bug in @vdblink::readString() readString@endlink related
  to empty strings.
  <I>[Contributed by Fabio&nbsp;Piparo]</I>
- Fixed a bug in the @vdblink::tools::VolumeToMesh VolumeToMesh@endlink
  simplification scheme that was creating visual artifacts.

@par
API changes:
- The addition of a
  @vdblink::GridBase::readBuffers(std::istream&, const CoordBBox&)
  GridBase::readBuffers@endlink virtual function overload and the
  @vdblink::GridBase::clip() GridBase::clip@endlink
  @vdblink::GridBase::readNonresidentBuffers()
  GridBase::readNonresidentBuffers@endlink and
  @vdblink::tree::Tree::clipUnallocatedNodes() Tree::clipUnallocatedNodes@endlink
  virtual functions changes the grid ABI so that it is incompatible with
  earlier versions of the OpenVDB library (such as the ones in Houdini 12.5
  and&nbsp;13).  Define the macro @c OPENVDB_2_ABI_COMPATIBLE when compiling
  OpenVDB to disable these changes and preserve ABI compatibility.
- All @vdblink::tools::BaseShader shaders@endlink now have a template argument
  to specify the type of an optional material color grid, but the default type
  mimics the old, uniform color behavior.
- Removed a deprecated
  @vdblink::io::Stream::write() io::Stream::write@endlink overload.
- The point counts in
  @vdblink::tools::UniformPointScatter UniformPointScatter@endlink
  and @vdblink::tools::NonUniformPointScatter NonUniformPointScatter@endlink
  are now specified and returned as @vdblink::Index64 Index64@endlink.
- @vdblink::math::RandInt RandInt@endlink has an extra template argument
  to specify the integer type.
  The @vdblink::math::RandomInt RandomInt@endlink typedef is unchanged.
- @vdblink::io::readData() io::readData@endlink,
  @vdblink::io::HalfReader<false,T>::read() io::HalfReader::read@endlink
  and @vdblink::io::HalfWriter<false,T>::write() io::HalfWriter::write@endlink
  now take a @c uint32_t argument indicating the type of compression
  instead of a @c bool indicating whether compression is enabled.
- Removed @c io::Archive::isCompressionEnabled() and
  @c io::Archive::setCompressionEnabled() and renamed
  @c io::Archive::compressionFlags() and @c io::Archive::setCompressionFlags()
  to @vdblink::io::Archive::compression() io::Archive::compression@endlink and
  @vdblink::io::Archive::setCompression() io::Archive::setCompression@endlink.
- Internal and leaf node classes are now required to provide
  "PartialCreate" constructors that optionally bypass the allocation
  of voxel buffers.  Leaf node classes must now also provide
  @vdblink::tree::LeafNode::allocate() allocate@endlink and
  @vdblink::tree::LeafNode::isAllocated() isAllocated@endlink methods
  to manage the allocation of their buffers.
- Removed @c pruneInactive and @c pruneLevelSet methods from the
  @vdblink::tree::Tree Tree@endlink and various node classes.
  These methods have been replaced by the much faster pruning functions
  found in tools/Prune.h.
- Removed @c signedFloodFill methods from the @vdblink::Grid Grid@endlink,
  @vdblink::tree::Tree Tree@endlink and various node classes.
  These methods have been replaced by the much faster functions
  found in tools/SignedFloodFill.h.
- Removed @c Grid::setBackground() and @c Tree::setBackground() (use the
  faster @vdblink::tools::changeBackground() changeBackground@endlink tool
  instead), and removed the default argument from
  @vdblink::tree::RootNode::setBackground() RootNode::setBackground@endlink.

@par
Python:
- Added grid methods @c convertToPolygons() and @c convertToQuads(),
  which convert volumes to meshes, and @c createLevelSetFromPolygons(),
  which converts meshes to volumes.
  <A HREF="http://docs.scipy.org/doc/">NumPy</A> is required.

@par
Maya:
- Added an adaptive polygonal surface extraction node.

@par
Houdini:
- Added a new Resize Narrow Band SOP that can efficiently adjust the width
  of a level set&rsquo;s narrow band.  This allows, for example, for a
  level set to be created quickly from points or polygons with a very
  narrow band that is then quickly resized to a desired width.
- Fixed bugs in the Smooth Level Set and Reshape Level Set SOPs that
  caused them to ignore the selected discretization scheme.
- Added a Morph Level Set SOP.
- Added a From Points SOP to very quickly generate a level set
  from a point cloud, ignoring any radius attribute.
  <I>[DWA internal]</I>
- Added a Voxel Scale mode to the Resample SOP.
- Improved the performance and memory footprint of the From Particles SOP
  for large numbers (tens to hundreds of millions) of particles.
- The Scatter SOP now accepts fractional numbers of particles per voxel.
- Improved the performance of the Scatter SOP by more than an order
  of magnitude.
- The Clip SOP now has a toggle to choose explicitly between a mask grid
  or a bounding box as the clipping region.  As a consequence, the mask grid
  can now be unnamed.
- Added the OpenVDB library version number to the Extended Operator
  Information for all SOPs.
- SOPs are now linked with an rpath to the directory containing the
  OpenVDB library.
- Like the native Houdini file SOP, the Read SOP now allows missing frames
  to be reported either as errors or as warnings.
- The Read SOP now has an optional input for geometry, the bounding box
  of which can be used to clip grids as they are read.  For large grids,
  clipping while reading can result in significantly lower memory usage
  than clipping after reading.
- The From Polygons and Convert SOPs now default to using the polygon soup
  mesh representation, which uses less memory.

@htmlonly <a name="v2_3_0_changes"></a>@endhtmlonly
@par
<B>Version 2.3.0</B> - <I>April 23, 2014</I>
- Added @vdblink::tools::extractSparseTree() extractSparseTree@endlink,
  which selectively extracts and transforms data from a dense grid to
  produce a sparse tree, and @vdblink::tools::extractSparseTreeWithMask()
  extractSparseTreeWithMask@endlink, which copies data from the index-space
  intersection of a sparse tree and a dense input grid.
- Added copy constructors to the
  @vdblink::Grid::Grid(const Grid<OtherTreeType>&) Grid@endlink,
  @vdblink::tree::Tree::Tree(const Tree<OtherRootType>&) Tree@endlink,
  @vdblink::tree::RootNode::RootNode(const RootNode<OtherChildType>&)
  RootNode@endlink,
  @vdblink::tree::InternalNode::InternalNode(const InternalNode<OtherChildNodeType, Log2Dim>&)
  InternalNode@endlink and
  @vdblink::tree::LeafNode::LeafNode(const LeafNode<OtherValueType, Log2Dim>&) LeafNode@endlink
  classes, and an assignment operator overload to
  @vdblink::tree::RootNode::operator=(const RootNode<OtherChildType>&)
  RootNode@endlink, that allow the source and destination to have different
  value types.
- Modified @vdblink::tree::Tree::combine2() Tree::combine2@endlink to permit
  combination of trees with different value types.
- Added @vdblink::CanConvertType CanConvertType@endlink and
  @vdblink::tree::RootNode::SameConfiguration
  RootNode::SameConfiguration@endlink metafunctions, which perform compile-time
  tests for value type and tree type compatibility, and a
  @vdblink::tree::RootNode::hasCompatibleValueType()
  RootNode::hasCompatibleValueType@endlink method, which does runtime checking.
- Added optional support for logging using
  <A HREF="http://log4cplus.sourceforge.net/">log4cplus</A>.
  See logging.h and the @c INSTALL file for details.
- Added  @vdblink::tools::VolumeRayIntersector::hits()
  VolumeRayIntersector::hits@endlink, which returns all the hit segments
  along a ray.  This is generally more efficient than repeated calls to
  @vdblink::tools::VolumeRayIntersector::march()
  VolumeRayIntersector::march@endlink.
- Added member class @vdblink::math::Ray::TimeSpan Ray::TimeSpan@endlink
  and method @vdblink::math::Ray::valid() Ray::valid@endlink, and deprecated
  method @vdblink::math::Ray::test() Ray::test@endlink.
- Fixed a bug in @vdblink::math::VolumeHDDA VolumeHDDA@endlink that could
  cause rendering artifacts when a ray&rsquo;s start time was zero.
  <I>[Contributed&nbsp;by&nbsp;Mike&nbsp;Farnsworth]</I>
- Added a @vdblink::tools::compositeToDense() compositeToDense@endlink tool,
  which composites data from a sparse tree into a dense array, using a
  sparse alpha mask.  Over, Add, Sub, Min, Max, Mult, and Set are
  supported operations.
- Added a @vdblink::tools::transformDense() transformDense@endlink tool,
  which applies a functor to the value of each voxel of a dense grid
  within a given bounding box.
- Improved the performance of node iterators.

@par
API changes:
- Collected the digital differential analyzer code from math/Ray.h
  and tools/RayIntersector.h into a new header file, math/DDA.h.
- Rewrote @vdblink::math::VolumeHDDA VolumeHDDA@endlink and made several
  changes to its API.  (@vdblink::math::VolumeHDDA VolumeHDDA@endlink
  is used internally by @vdblink::tools::VolumeRayIntersector
  VolumeRayIntersector@endlink, whose API is unchanged.)
- @vdblink::tree::Tree::combine2() Tree::combine2@endlink,
  @vdblink::tree::RootNode::combine2() RootNode::combine2@endlink,
  @vdblink::tree::InternalNode::combine2() InternalNode::combine2@endlink,
  @vdblink::tree::LeafNode::combine2() LeafNode::combine2@endlink
  and @vdblink::CombineArgs CombineArgs@endlink all now require an additional
  template argument, which determines the type of the other tree.
- Assignment operators for
  @vdblink::tree::LeafManager::LeafRange::Iterator::operator=()
  LeafManager::LeafRange::Iterator@endlink,
  @vdblink::util::BaseMaskIterator::operator=() BaseMaskIterator@endlink,
  @vdblink::util::NodeMask::operator=() NodeMask@endlink and
  @vdblink::util::RootNodeMask::operator=() RootNodeMask@endlink
  now return references to the respective objects.
- Removed a number of methods that were deprecated in version&nbsp;2.0.0
  or earlier.

@par
Houdini:
- Added a Clip SOP, which does volumetric clipping.
- Added an Occlusion Mask SOP, which generates a mask of the voxels
  inside a camera frustum that are occluded by objects in an input grid.
- The Combine SOP now applies the optional signed flood fill only to
  level set grids, since that operation isn&rsquo;t meaningful for other grids.
- The Filter SOP now processes all grid types, not just scalar grids.


@htmlonly <a name="v2_2_0_changes"></a>@endhtmlonly
@par
<B>Version 2.2.0</B> - <I>February 20, 2014</I>
- Added a simple, multithreaded
  @vdblink::tools::VolumeRender volume renderer@endlink,
  and added volume rendering support to the @c vdb_render
  command-line renderer.
- Added an option to the
  @vdblink::tools::LevelSetRayIntersector LevelSetRayIntersector@endlink
  and to @c vdb_render to specify the isovalue of the level set.
- Added methods to the
  @vdblink::tools::LevelSetRayIntersector LevelSetRayIntersector@endlink
  to return the time of intersection along a world or index ray and to
  return the level set isovalue.
- Improved the performance of the
  @vdblink::tools::VolumeRayIntersector VolumeRayIntersector@endlink
  and added support for voxel dilation to account for interpolation kernels.
- Added a @ref sInterpolation "section" to the Cookbook on interpolation
  using @vdblink::tools::BoxSampler BoxSampler@endlink,
  @vdblink::tools::GridSampler GridSampler@endlink,
  @vdblink::tools::DualGridSampler DualGridSampler@endlink, et al.
- Added a @ref secGrid "section" to the Overview on grids and grid metadata.
- Modified @vdblink::tools::DualGridSampler DualGridSampler@endlink so
  it is more consistent with @vdblink::tools::GridSampler GridSampler@endlink.
- The @vdblink::tools::cpt() cpt@endlink, @vdblink::tools::curl() curl@endlink,
  @vdblink::tools::laplacian() laplacian@endlink,
  @vdblink::tools::meanCurvature() meanCurvature@endlink
  and @vdblink::tools::normalize() normalize@endlink tools now output grids
  with appropriate @vdblink::VecType vector types@endlink
  (covariant, contravariant, etc.).
- Added a @vdblink::tools::transformVectors() transformVectors@endlink tool,
  which applies an affine transformation to the voxel values of a
  vector-valued grid in accordance with the grid&rsquo;s
  @vdblink::VecType vector type@endlink and
  @vdblink::Grid::isInWorldSpace() world space/local space@endlink setting.
- Added a @vdblink::tools::compDiv() compDiv@endlink tool, which combines
  grids by dividing the values of corresponding voxels.
- Fixed a bug in the mean curvature computation that could produce NaNs
  in regions with constant values.
- Added a
  @vdblink::Grid::topologyDifference() Grid::topologyDifference@endlink method.
- Added @vdblink::math::Vec3::exp() exp@endlink and
  @vdblink::math::Vec3::sum() sum@endlink methods to
  @vdblink::math::Vec2 Vec2@endlink, @vdblink::math::Vec3 Vec3@endlink
  and @vdblink::math::Vec4 Vec4@endlink.
- Improved the @vdblink::tools::fillWithSpheres() fillWithSpheres@endlink
  tool for small volumes that are just a few voxels across.
- Improved the accuracy of the mesh to volume converter.
- Fixed a bug in the mesh to volume converter that caused incorrect sign
  classifications for narrow-band level sets.
- Fixed a bug in @vdblink::math::NonlinearFrustumMap::applyIJT()
  NonlinearFrustumMap::applyIJT@endlink that resulted in incorrect values
  when computing the gradient of a grid with a frustum transform.
- Fixed a file I/O bug whereby some <TT>.vdb</TT> files could not be read
  correctly if they contained grids with more than two distinct inactive
  values.
- Fixed an off-by-one bug in the numbering of unnamed grids in <TT>.vdb</TT>
  files.  The first unnamed grid in a file is now retrieved using the name
  &ldquo;<TT>[0]</TT>&rdquo;, instead of &ldquo;<TT>[1]</TT>&rdquo;.
- Fixed a build issue reported by Clang&nbsp;3.2 in tools/GridOperators.h.
- Fixed a memory leak in @vdblink::tools::Film Film@endlink.
- Added library and file format version number constants to the Python module.
- Improved convergence in the
  @vdblink::tools::VolumeRender volume renderer@endlink.
  <I>[Contributed by Jerry Tessendorf and Mark Matthews]</I>
- Made various changes for compatibility with Houdini&nbsp;13 and with
  C++11 compilers.
  <I>[Contributed&nbsp;by&nbsp;SESI]</I>

@par
API changes:
- @vdblink::tools::VolumeRayIntersector::march()
  VolumeRayIntersector::march@endlink no longer returns an @c int
  to distinguish tile vs. voxel hits.  Instead, it now returns @c false
  if no intersection is detected and @c true otherwise.  Also, @e t0 and
  @e t1 might now correspond to the first and last hits of multiple adjacent
  leaf nodes and/or active tiles.
- @vdblink::tools::DualGridSampler DualGridSampler@endlink is no longer
  templated on the target grid type, and the value accessor is now passed
  as an argument.
- The <TT>.vdb</TT> file format has changed slightly.  Tools built with older
  versions of OpenVDB should be recompiled to ensure that they can read files
  in the new format.

@par
Houdini:
- Added topology union, intersection and difference operations to
  the Combine SOP.  These operations combine the active voxel topologies
  of grids that may have different value types.
- Added a Divide operation to the Combine SOP.
- Added support for boolean grids to the Combine, Resample, Scatter, Prune
  and Visualize SOPs.
- The Fill SOP now accepts a vector as the fill value, and it allows
  the fill region bounds to be specified either in index space (as before),
  in world space, or using the bounds of geometry connected to an optional
  new reference input.
- Added a toggle to the Offset Level Set SOP to specify the offset in
  either world or voxel units.
- Added a toggle to the Transform and Resample SOPs to apply the transform
  to the voxel values of vector-valued grids, in accordance with those
  grids&rsquo; @vdblink::VecType vector types@endlink and
  @vdblink::Grid::isInWorldSpace() world space/local space@endlink settings.
- Added a Vector Type menu to the Vector Merge SOP.
- Removed masking options from the Renormalize SOP (since masking is
  not supported yet).
- Reimplemented the Vector Merge SOP for better performance and
  interruptibility and to fix a bug in the handling of tile values.


@htmlonly <a name="v2_1_0_changes"></a>@endhtmlonly
@par
<B>Version 2.1.0</B> - <I>December 12, 2013</I>
- Added a small number of Maya nodes, primarily for conversion of geometry
  to and from OpenVDB volumes and for visualization of volumes.
- Added an initial implementation of
  @vdblink::tools::LevelSetMorphing level set morphing@endlink
  (with improvements to follow soon).
- Added @vdblink::tools::LevelSetMeasure tools::LevelSetMeasure@endlink,
  which efficiently computes the surface area, volume and average
  mean-curvature of narrow-band level sets, in both world and voxel units.
  Those quantities are now exposed as intrinsic attributes on the Houdini
  VDB primitive and can be queried using the native Measure SOP.
- @vdblink::tools::Dense tools::Dense@endlink now supports the XYZ memory
  layout used by Houdini and Maya in addition to the ZYX layout used in
  OpenVDB trees.
- Improved the performance of masking in the
  @vdblink::tools::LevelSetFilter level set filter@endlink tool and
  added inversion and scaling of the mask input, so that any scalar-valued
  volume can be used as a mask, not just volumes with a [0,&nbsp;1] range.
- Added optional masking to the non-level-set filters, to the grid
  operators (CPT, curl, divergence, gradient, Laplacian, mean curvature,
  magnitude, and normalize) and to the Analysis and Filter SOPs.
- Added more narrow band controls to the Rebuild Level Set SOP.
- Improved the accuracy of the
  @vdblink::tools::levelSetRebuild() level set rebuild@endlink tool.
- Added @vdblink::tools::activate() tools::activate@endlink and
  @vdblink::tools::deactivate() tools::deactivate@endlink, which set the
  active states of tiles and voxels whose values are equal to or approximately
  equal to a given value, and added a Deactivate Background Voxels toggle
  to the Combine SOP.
- Added @vdblink::math::BBox::applyMap() BBox::applyMap@endlink and
  @vdblink::math::BBox::applyInverseMap() BBox::applyInverseMap@endlink,
  which allow for transformation of axis-aligned bounding boxes.
- Added a @vdblink::tools::PositionShader position shader@endlink to the
  level set ray-tracer (primarily for debugging purposes).
- Added an @vdblink::io::Queue io::Queue@endlink class that manages a
  concurrent queue for asynchronous serialization of grids to files or streams.
- Fixed a bug in @vdblink::io::Archive io::Archive@endlink whereby writing
  unnamed, instanced grids (i.e., grids sharing a tree) to a file rendered
  the file unreadable.
- Fixed a bug in the @vdblink::tools::VolumeToMesh volume to mesh@endlink
  converter that caused it to generate invalid polygons when the zero crossing
  lay between active and inactive regions.
- Fixed a bug in the @vdblink::tools::UniformPointScatter point scatter@endlink
  tool (and the Scatter SOP) whereby the last voxel always remained empty.
- Fixed a bug in the Read SOP that caused grids with the same name
  to be renamed with a numeric suffix (e.g., &ldquo;grid[1]&rdquo;
  &ldquo;grid[2]&rdquo;, etc.).
- Fixed some unit test failures on 64-bit Itanium machines.

@par
API changes:
- The @vdblink::tools::Filter Filter@endlink tool is now templated on a
  mask grid, and threading is controlled using a grain size, for consistency
  with most of the other level set tools.
- The @vdblink::tools::LevelSetFilter LevelSetFilter@endlink tool is now
  templated on a mask grid.
- All shaders now take a ray direction instead of a ray.


@htmlonly <a name="v2_0_0_changes"></a>@endhtmlonly
@par
<B>Version 2.0.0</B> - <I>October 31, 2013</I>
- Added a @ref python "Python module" with functions for basic manipulation
  of grids (but no tools, yet).
- Added ray intersector tools for efficient, hierarchical intersection
  of rays with @vdblink::tools::LevelSetRayIntersector level-set@endlink
  and @vdblink::tools::VolumeRayIntersector generic@endlink volumes.
- Added a @vdblink::math::Ray Ray@endlink class and a hierarchical
  @vdblink::math::DDA Digital Differential Analyzer@endlink for fast
  ray traversal.
- Added a fully multi-threaded @vdblink::tools::LevelSetRayTracer
  level set ray tracer@endlink and
  @vdblink::tools::PerspectiveCamera camera@endlink
  @vdblink::tools::OrthographicCamera classes@endlink
  that mimic Houdini&rsquo;s cameras.
- Added a simple, command-line renderer (currently for level sets only).
- Implemented a new meshing scheme that produces topologically robust
  two-manifold meshes and is twice as fast as the previous scheme.
- Implemented a new, topologically robust (producing two-manifold meshes)
  level-set-based seamless fracture scheme.  The new scheme eliminates
  visible scarring seen in the previous implementation by subdividing
  internal, nonplanar quads near fracture seams.  In addition,
  fracture seam points are now tagged, allowing them to be used
  to drive pre-fracture dynamics such as local surface buckling.
- Improved the performance of @vdblink::tree::Tree::evalActiveVoxelBoundingBox()
  Tree::evalActiveVoxelBoundingBox@endlink and
  @vdblink::tree::Tree::activeVoxelCount() Tree::activeVoxelCount@endlink,
  and significantly improved the performance of
  @vdblink::tree::Tree::evalLeafBoundingBox() Tree::evalLeafBoundingBox@endlink
  (by about&nbsp;30x).
- Added a tool (and a Houdini SOP) that fills a volume with
  adaptively-sized overlapping or non-overlapping spheres.
- Added a Ray SOP that can be used to perform geometry projections
  using level-set ray intersections or closest-point queries.
- Added a @vdblink::tools::ClosestSurfacePoint tool@endlink that performs
  accelerated closest surface point queries from arbitrary points in
  world space to narrow-band level sets.
- Increased the speed of masked level set filtering by 20% for
  the most common cases.
- Added @vdblink::math::BoxStencil math::BoxStencil@endlink, with support
  for trilinear interpolation and gradient computation.
- Added @vdblink::tree::Tree::topologyIntersection()
  Tree::topologyIntersection@endlink, which intersects a tree&rsquo;s active
  values with those of another tree, and
  @vdblink::tree::Tree::topologyDifference() Tree::topologyDifference@endlink,
  which performs topological subtraction of one tree&rsquo;s active values
  from another&rsquo;s.  In both cases, the <TT>ValueType</TT>s of the two
  trees need not be the same.
- Added @vdblink::tree::Tree::activeTileCount() Tree::activeTileCount@endlink,
  which returns the number of active tiles in a tree.
- Added @vdblink::math::MinIndex() math::MinIndex@endlink and
  @vdblink::math::MaxIndex() math::MaxIndex@endlink, which find the minimum
  and maximum components of a vector without any branching.
- Added @vdblink::math::BBox::minExtent() BBox::minExtent@endlink,
  which returns a bounding box&rsquo;s shortest axis.
- The default @vdblink::math::BBox BBox@endlink constructor now
  generates an invalid bounding box rather than an empty bounding box
  positioned at the origin.  The new behavior is consistent with
  @vdblink::math::CoordBBox CoordBBox@endlink.
  <I>[Thanks to Rick Hankins for suggesting this fix.]</I>
- Added @vdblink::math::CoordBBox::reset() CoordBBox::reset@endlink,
  which resets a bounding box to its initial, invalid state.
- Fixed a bug in the default @vdblink::math::ScaleMap ScaleMap@endlink
  constructor that left some data used in the inverse uninitialized.
- Added @vdblink::math::MapBase::applyJT MapBase::applyJT@endlink, which
  applies the Jacobian transpose to a vector (the Jacobian transpose takes
  a range-space vector to a domain-space vector, e.g., world to index),
  and added @vdblink::math::MapBase::inverseMap() MapBase::inverseMap@endlink,
  which returns a new map representing the inverse of the original map
  (except for @vdblink::math::NonlinearFrustumMap NonlinearFrustumMap@endlink,
  which does not currently have a defined inverse map).
  <br>@b Note: Houdini 12.5 uses an earlier version of OpenVDB, and maps
  created with that version lack virtual table entries for these
  new methods, so do not call these methods from Houdini&nbsp;12.5.
- Reimplemented @vdblink::math::RandomInt math::RandomInt@endlink using
  Boost.Random instead of @c rand() (which is not thread-safe), and deprecated
  @c math::randUniform() and added
  @vdblink::math::Random01 math::Random01@endlink to replace it.
- Modified @vdblink::tools::copyFromDense() tools::copyFromDense@endlink
  and @vdblink::tools::copyToDense() tools::copyToDense@endlink to allow
  for implicit type conversion (e.g., between a
  @vdblink::tools::Dense Dense&lt;Int32&gt;@endlink and a
  @vdblink::FloatTree FloatTree@endlink) and fixed several bugs
  in @vdblink::tools::CopyFromDense tools::CopyFromDense@endlink.
- Fixed bugs in @vdblink::math::Stats math::Stats@endlink and
  @vdblink::math::Histogram math::Histogram@endlink that could produce
  <TT>NaN</TT>s or other incorrect behavior if certain methods were called
  on populations of size zero.
- Renamed <TT>struct tolerance</TT> to
  @vdblink::math::Tolerance math::Tolerance@endlink
  and @c negative to @vdblink::math::negative() math::negative@endlink
  and removed @c math::toleranceValue().
- Implemented a closest point on line segment algorithm,
  @vdblink::math::closestPointOnSegmentToPoint()
  math::closestPointOnSegmentToPoint@endlink.
- Fixed meshing issues relating to masking and automatic partitioning.
- @vdblink::Grid::merge() Grid::merge@endlink and
  @vdblink::tree::Tree::merge() Tree::merge@endlink now accept an optional
  @vdblink::MergePolicy MergePolicy@endlink argument that specifies one of
  three new merging schemes.  (The old merging scheme, which is no longer
  available, used logic for each tree level that was inconsistent with
  the other levels and that could result in active tiles being replaced
  with nodes having only inactive values.)
- Renamed @c LeafNode::coord2offset(), @c LeafNode::offset2coord() and
  @c LeafNode::offset2globalCoord() to
  @vdblink::tree::LeafNode::coordToOffset() coordToOffset@endlink,
  @vdblink::tree::LeafNode::offsetToLocalCoord() offsetToLocalCoord@endlink,
  and @vdblink::tree::LeafNode::offsetToGlobalCoord()
  offsetToGlobalCoord@endlink, respectively, and likewise for
  @vdblink::tree::InternalNode::offsetToGlobalCoord() InternalNode@endlink.
  <I>[Thanks to Rick Hankins for suggesting this change.]</I>
- Replaced @vdblink::tree::Tree Tree@endlink methods @c setValueOnMin,
  @c setValueOnMax and @c setValueOnSum with
  @vdblink::tools::setValueOnMin() tools::setValueOnMin@endlink,
  @vdblink::tools::setValueOnMax() tools::setValueOnMax@endlink and
  @vdblink::tools::setValueOnSum() tools::setValueOnSum@endlink
  (and a new @vdblink::tools::setValueOnMult() tools::setValueOnMult@endlink)
  and added @vdblink::tree::Tree::modifyValue() Tree::modifyValue@endlink
  and @vdblink::tree::Tree::modifyValueAndActiveState()
  Tree::modifyValueAndActiveState@endlink, which modify voxel values
  in-place via user-supplied functors.  Similarly, replaced
  @c ValueAccessor::setValueOnSum() with
  @vdblink::tree::ValueAccessor::modifyValue()
  ValueAccessor::modifyValue@endlink
  and @vdblink::tree::ValueAccessor::modifyValueAndActiveState()
  ValueAccessor::modifyValueAndActiveState@endlink, and added a
  @vdblink::tree::TreeValueIteratorBase::modifyValue() modifyValue@endlink
  method to all value iterators.
- Removed @c LeafNode::addValue and @c LeafNode::scaleValue.
- Added convenience classes @vdblink::tree::Tree3 tree::Tree3@endlink and
  @vdblink::tree::Tree5 tree::Tree5@endlink for custom tree configurations.
- Added an option to the From Particles SOP to generate an alpha mask,
  which can be used to constrain level set filtering so as to preserve
  surface details.
- The mesh to volume converter now handles point-degenerate polygons.
- Fixed a bug in the Level Set Smooth, Level Set Renormalize and
  Level Set Offset SOPs that caused the group name to be ignored.
- Fixed various OS X and Windows build issues.
  <I>[Contributions from SESI and DD]</I>


@htmlonly <a name="v1_2_0_changes"></a>@endhtmlonly
@par
<B>Version 1.2.0</B> - <I>June 28 2013</I>
- @vdblink::tools::LevelSetFilter Level set filters@endlink now accept
  an optional alpha mask grid.
- Implemented sharp feature extraction for level set surfacing.
  This enhances the quality of the output mesh and reduces aliasing
  artifacts.
- Added masking options to the meshing tools, as well as a spatial
  multiplier for the adaptivity threshold, automatic partitioning,
  and the ability to preserve edges and corners when mesh adaptivity
  is applied.
- The mesh to volume attribute transfer scheme now takes surface
  orientation into account, which improves accuracy in proximity to
  edges and corners.
- Added a @vdblink::tree::LeafManager::foreach() foreach@endlink method
  to @vdblink::tree::LeafManager tree::LeafManager@endlink that, like
  @vdblink::tools::foreach() tools::foreach@endlink, applies a user-supplied
  functor to each leaf node in parallel.
- Rewrote the particle to level set converter, simplifying the API,
  improving performance (especially when particles have a fixed radius),
  adding the capability to transfer arbitrary point attributes,
  and fixing a velocity trail bug.
- Added utility methods @vdblink::math::Sign() Sign@endlink,
  @vdblink::math::SignChange() SignChange@endlink,
  @vdblink::math::isApproxZero() isApproxZero@endlink,
  @vdblink::math::Cbrt() Cbrt@endlink and
  @vdblink::math::ZeroCrossing() ZeroCrossing@endlink to math/Math.h.
- Added a @vdblink::tree::ValueAccessor3::probeNode() probeNode@endlink method
  to the value accessor and to tree nodes that returns a pointer to the node
  that contains a given voxel.
- Deprecated @c LeafNode::addValue and @c LeafNode::scaleValue.
- Doubled the speed of the mesh to volume converter (which also improves
  the performance of the fracture and level set rebuild tools) and
  improved its inside/outside voxel classification near edges and corners.
- @vdblink::tools::GridSampler GridSampler@endlink now accepts either a grid,
  a tree or a value accessor, and it offers faster index-based access methods
  and much better performance in cases where many instances are allocated.
- Extended @vdblink::tools::Dense tools::Dense@endlink to make it more
  compatible with existing tools.
- Fixed a crash in @vdblink::io::Archive io::Archive@endlink whenever
  the library was unloaded from memory and then reloaded.
  <I>[Contributed by Ollie Harding]</I>
- Fixed a bug in @c GU_PrimVDB::buildFromPrimVolume(), seen during the
  conversion from Houdini volumes to OpenVDB grids, that could cause
  signed flood fill to be applied to non-level set grids, resulting in
  active tiles with incorrect values.
- Added a Prune SOP with several pruning schemes.


@htmlonly <a name="v1_1_1_changes"></a>@endhtmlonly
@par
<B>Version 1.1.1</B> - <I>May 10 2013</I>
- Added a simple @vdblink::tools::Dense dense grid class@endlink and tools
  to copy data from dense voxel arrays into OpenVDB grids and vice-versa.
- Starting with Houdini 12.5.396, plugins built with this version
  of OpenVDB can coexist with native Houdini OpenVDB nodes.
- The level set fracture tool now smooths seam line edges during
  mesh extraction, eliminating staircase artifacts.
- Significantly improved the performance of the
  @vdblink::util::leafTopologyIntersection()
  leafTopologyIntersection@endlink and
  @vdblink::util::leafTopologyDifference() leafTopologyDifference@endlink
  utilities and added a @vdblink::tree::LeafNode::topologyDifference()
  LeafNode::topologyDifference@endlink method.
- Added convenience functions that provide simplified interfaces
  to the @vdblink::tools::meshToLevelSet() mesh to volume@endlink
  and @vdblink::tools::volumeToMesh() volume to mesh@endlink converters.
- Added a @vdblink::tools::accumulate() tools::accumulate@endlink function
  that is similar to @vdblink::tools::foreach() tools::foreach@endlink
  but can be used to accumulate the results of computations over the values
  of a grid.
- Added @vdblink::tools::statistics() tools::statistics@endlink,
  @vdblink::tools::opStatistics() tools::opStatistics@endlink and
  @vdblink::tools::histogram() tools::histogram@endlink, which efficiently
  compute statistics (mean, variance, etc.) and histograms of grid values
  (using @vdblink::math::Stats math::Stats@endlink and
  @vdblink::math::Histogram math::Histogram@endlink).
- Modified @vdblink::math::CoordBBox CoordBBox@endlink to adhere to
  TBB&rsquo;s splittable type requirements, so that, for example,
  a @c CoordBBox can be used as a blocked iteration range.
- Added @vdblink::tree::Tree::addTile() Tree::addTile@endlink,
  @vdblink::tree::Tree::addLeaf() Tree::addLeaf@endlink and
  @vdblink::tree::Tree::stealNode() Tree::stealNode@endlink, for fine
  control over tree construction.
- Addressed a numerical stability issue when performing Gaussian
  filtering of level set grids.
- Changed the return type of @vdblink::math::CoordBBox::volume()
  CoordBBox::volume@endlink to reduce the risk of overflow.
- When the input mesh is self-intersecting, the mesh to volume converter
  now produces a level set with a monotonic gradient field.
- Fixed a threading bug in the mesh to volume converter that caused it
  to produce different results for the same input.
- Fixed a bug in the particle to level set converter that prevented
  particles with zero velocity from being rasterized in Trail mode.
- Added an optional input to the Create SOP into which to merge
  newly-created grids.
- Fixed a bug in the Resample SOP that caused it to produce incorrect
  narrow-band widths when resampling level set grids.
- Fixed a bug in the To Polygons SOP that caused intermittent crashes
  when the optional reference input was connected.
- Fixed a bug in the Advect Level Set SOP that caused a crash
  when the velocity input was connected but empty.
- The Scatter and Sample Point SOPs now warn instead of erroring
  when given empty grids.
- Fixed a crash in @c vdb_view when stepping through multiple grids
  after changing render modes.
- @c vdb_view can now render fog volumes and vector fields, and it now
  features interactively adjustable clipping planes that enable
  one to view the interior of a volume.


@htmlonly <a name="v1_1_0_changes"></a>@endhtmlonly
@par
<B>Version 1.1.0</B> - <I>April 4 2013</I>
- The @vdblink::tools::resampleToMatch() resampleToMatch@endlink tool,
  the Resample SOP and the Combine SOP now use level set rebuild to correctly
  and safely resample level sets.  Previously, scaling a level set would
  invalidate the signed distance field, leading to holes and other artifacts.
- Added a mask-based topological
  @vdblink::tools::erodeVoxels erosion tool@endlink, and rewrote and
  simplified the @vdblink::tools::dilateVoxels dilation tool@endlink.
- The @vdblink::tools::LevelSetAdvection LevelSetAdvection@endlink tool
  can now advect forward or backward in time.
- Tree::pruneLevelSet() now replaces each pruned node with a tile having
  the inside or outside
  background value, instead of arbitrarily selecting one of the node&rsquo;s
  tile or voxel values.
- When a grid is saved to a file with
  @vdblink::Grid::saveFloatAsHalf() saveFloatAsHalf@endlink set to @c true,
  the grid&rsquo;s background value is now also quantized to 16 bits.
  (Not quantizing the background value caused a mismatch with the values
  of background tiles.)
- As with @vdblink::tools::foreach() tools::foreach@endlink, it is now
  possible to specify whether functors passed to
  @vdblink::tools::transformValues() tools::transformValues@endlink
  should be shared across threads.
- @vdblink::tree::LeafManager tree::LeafManager@endlink can now be
  instantiated with a @const tree, although buffer swapping with @const trees
  is disabled.
- Added a @vdblink::Grid::signedFloodFill() Grid::signedFloodFill@endlink
  overload that allows one to specify inside and outside values.
- Fixed a bug in Grid::setBackground() so that now only the values of
  inactive voxels change.
- Fixed @vdblink::Grid::topologyUnion() Grid::topologyUnion@endlink so that
  it actually unions tree topology, instead of just the active states
  of tiles and voxels.  The previous behavior broke multithreaded code
  that relied on input and output grids having compatible tree topology.
- @vdblink::math::Transform math::Transform@endlink now includes an
  @vdblink::math::Transform::isIdentity() isIdentity@endlink predicate
  and methods to @vdblink::math::Transform::preMult(const Mat4d&) pre-@endlink
  and @vdblink::math::Transform::postMult(const Mat4d&) postmultiply@endlink
  by a matrix.
- Modified the @link NodeMasks.h node mask@endlink classes to permit
  octree-like tree configurations (i.e., with a branching factor of two)
  and to use 64-bit operations instead of 32-bit operations.
- Implemented a new, more efficient
  @vdblink::math::closestPointOnTriangleToPoint() closest point
  on triangle@endlink algorithm.
- Implemented a new vertex normal scheme in the volume to mesh
  converter, and resolved some overlapping polygon issues.
- The volume to mesh converter now meshes not just active voxels
  but also active tiles.
- Fixed a bug in the mesh to volume converter that caused unsigned
  distance field conversion to produce empty grids.
- Fixed a bug in the level set fracture tool whereby the cutter overlap
  toggle was ignored.
- Fixed an infinite loop bug in @c vdb_view.
- Updated @c vdb_view to use the faster and less memory-intensive
  OpenVDB volume to mesh converter instead of marching cubes,
  and rewrote the shader to be OpenGL 3.2 and GLSL 1.2 compatible.
- Given multiple input files or a file containing multiple grids,
  @c vdb_view now displays one grid at a time.  The left and right
  arrow keys cycle between grids.
- The To Polygons SOP now has an option to associate the input grid&rsquo;s
  name with each output polygon.


@htmlonly <a name="v1_0_0_changes"></a>@endhtmlonly
@par
<B>Version 1.0.0</B> - <I>March 14 2013</I>
- @vdblink::tools::levelSetRebuild() tools::levelSetRebuild@endlink
  now throws an exception when given a non-scalar or non-floating-point grid.
- The tools in tools/GridOperators.h are now interruptible, as is
  the Analysis SOP.
- Added a
  @vdblink::tree::LeafManager::LeafRange::Iterator leaf node iterator@endlink
  and a TBB-compatible
  @vdblink::tree::LeafManager::LeafRange range class@endlink
  to the LeafManager.
- Modified the @vdblink::tools::VolumeToMesh VolumeToMesh@endlink tool
  to handle surface topology issues around fracture seam lines.
- Modified the Makefile to allow @c vdb_view to compile on OS X systems
  (provided that GLFW is available).
- Fixed a bug in the Create SOP that resulted in "invalid parameter name"
  warnings.
- The Combine SOP now optionally resamples the A grid into the B grid&rsquo;s
  index space (or vice-versa) if the A and B transforms differ.
- The Vector Split and Vector Merge SOPs now skip inactive voxels
  by default, but they can optionally be made to include inactive voxels,
  as they did before.
- The @vdblink::tools::LevelSetFracture LevelSetFracture@endlink tool now
  supports custom rotations for each cutter instance, and the Fracture SOP
  now uses quaternions to generate uniformly-distributed random rotations.


@htmlonly <a name="v0_104_0_changes"></a>@endhtmlonly
@par
<B>Version 0.104.0</B> - <I>February 15 2013</I>
- Added a @vdblink::tools::levelSetRebuild() tool@endlink and a SOP
  to rebuild a level set from any scalar volume.
- @c .vdb files are now saved using a mask-based compression scheme
  that is an order of magnitude faster than ZLIB and produces comparable
  file sizes for level set and fog volume grids.  (ZLIB compression
  is still enabled by default for other classes of grids).
- The @vdblink::tools::Filter Filter@endlink and
  @vdblink::tools::LevelSetFilter LevelSetFilter@endlink tools now
  include a Gaussian filter, and mean (box) filtering is now 10-50x faster.
- The isosurface @vdblink::tools::VolumeToMesh meshing tool@endlink
  is now more robust (to level sets with one voxel wide narrow bands,
  for example).
- Mesh to volume conversion is on average 1.5x faster and up to 5.5x
  faster for high-resolution meshes where the polygon/voxel size ratio
  is small.
- Added @vdblink::createLevelSet() createLevelSet@endlink and
  @vdblink::createLevelSetSphere() createLevelSetSphere@endlink
  factory functions for level set grids.
- @vdblink::tree::ValueAccessor tree::ValueAccessor@endlink is now faster
  for trees of height 2, 3 and 4 (the latter is the default), and it now
  allows one to specify, via a template argument, the number of node levels
  to be cached, which can also improve performance in special cases.
- Added a toggle to @vdblink::tools::foreach() tools::foreach@endlink
  to specify whether or not the functor should be shared across threads.
- Added @vdblink::Mat4SMetadata Mat4s@endlink and
  @vdblink::Mat4DMetadata Mat4d@endlink metadata types.
- Added explicit pre- and postmultiplication methods to the @c Transform,
  @c Map and @c Mat4 classes and deprecated the old accumulation methods.
- Modified @vdblink::math::NonlinearFrustumMap NonlinearFrustumMap@endlink
  to be more compatible with Houdini&rsquo;s frustum transform.
- Fixed a @vdblink::tools::GridTransformer GridTransformer@endlink bug
  that caused it to translate the output grid incorrectly in some cases.
- Fixed a bug in the tree-level
  @vdblink::tree::LeafIteratorBase LeafIterator@endlink that resulted in
  intermittent crashes in
  @vdblink::tools::dilateVoxels() tools::dilateVoxels@endlink.
- The @c Hermite data type and Hermite grids are no longer supported.
- Added tools/GridOperators.h, which includes new, cleaner implementations
  of the @vdblink::tools::cpt() closest point transform@endlink,
  @vdblink::tools::curl() curl@endlink,
  @vdblink::tools::divergence() divergence@endlink,
  @vdblink::tools::gradient() gradient@endlink,
  @vdblink::tools::laplacian() Laplacian@endlink,
  @vdblink::tools::magnitude() magnitude@endlink,
  @vdblink::tools::meanCurvature() mean curvature@endlink and
  @vdblink::tools::normalize() normalize@endlink tools.
- Interrupt support has been improved in several tools, including
  @vdblink::tools::ParticlesToLevelSet tools::ParticlesToLevelSet@endlink.
- Simplified the API of the @vdblink::math::BaseStencil Stencil@endlink class
  and added an @vdblink::math::BaseStencil::intersects() intersects@endlink
  method to test for intersection with a specified isovalue.
- Renamed @c voxelDimensions to @c voxelSize in transform classes
  and elsewhere.
- Deprecated @c houdini_utils::ParmFactory::setChoiceList in favor of
  @c houdini_utils::ParmFactory::setChoiceListItems, which requires
  a list of <I>token, label</I> string pairs.
- Made various changes for Visual C++ compatibility.
  <I>[Contributed by SESI]</I>
- Fixed a bug in @c houdini_utils::getNodeChain() that caused the
  Offset Level Set, Smooth Level Set and Renormalize Level Set SOPs
  to ignore frame changes.
  <I>[Contributed by SESI]</I>
- The From Particles SOP now provides the option to write into
  an existing grid.
- Added a SOP to edit grid metadata.
- The Fracture SOP now supports multiple cutter objects.
- Added a To Polygons SOP that complements the Fracture SOP and allows
  for elimination of seam lines, generation of correct vertex normals
  and grouping of polygons when surfacing fracture fragments, using
  the original level set or mesh as a reference.


@htmlonly <a name="v0_103_1_changes"></a>@endhtmlonly
@par
<B>Version 0.103.1</B> - <I>January 15 2013</I>
- @vdblink::tree::ValueAccessor tree::ValueAccessor@endlink read operations
  are now faster for four-level trees.
  (Preliminary benchmark tests suggest a 30-40% improvement.)
- For vector-valued grids, @vdblink::tools::compMin() tools::compMin@endlink
  and @vdblink::tools::compMax() tools::compMax@endlink now compare
  vector magnitudes instead of individual components.
- Migrated grid sampling code to a new file, Interpolation.h,
  and deprecated old files and classes.
- Added a level-set @vdblink::tools::LevelSetFracture fracture tool@endlink
  and a Fracture SOP.
- Added @vdblink::tools::sdfInteriorMask() tools::sdfInteriorMask@endlink,
  which creates a mask of the interior region of a level set grid.
- Fixed a bug in the mesh to volume converter that produced unexpected
  nonzero values for voxels at the intersection of two polygons,
  and another bug that produced narrow-band widths that didn&rsquo;t respect
  the background value when the half-band width was less than three voxels.
- @c houdini_utils::ParmFactory can now correctly generate ramp multi-parms.
- Made various changes for Visual C++ compatibility.
  <I>[Contributed by SESI]</I>
- The Convert SOP can now convert between signed distance fields and
  fog volumes and from volumes to meshes.
  <I>[Contributed by SESI]</I>
- For level sets, the From Mesh and From Particles SOPs now match
  the reference grid&rsquo;s narrow-band width.
- The Scatter SOP can now optionally scatter points in the interior
  of a level set.


@htmlonly <a name="v0_103_0_changes"></a>@endhtmlonly
@par
<B>Version 0.103.0</B> - <I>December 21 2012</I>
- The mesh to volume converter is now 60% faster at generating
  level sets with wide bands, and the From Mesh SOP is now interruptible.
- Fixed a threading bug in the recently-added
  @vdblink::tools::compReplace() compReplace@endlink tool
  that caused it to produce incorrect output.
- Added a @vdblink::tree::Tree::probeConstLeaf() probeConstLeaf@endlink
  method to the @vdblink::tree::Tree::probeConstLeaf() Tree@endlink,
  @vdblink::tree::ValueAccessor::probeConstLeaf() ValueAccessor@endlink
  and @vdblink::tree::RootNode::probeConstLeaf() node@endlink classes.
- The Houdini VDB primitive doesn&rsquo;t create a @c name attribute
  unnecessarily (i.e., if its grid&rsquo;s name is empty), but it now
  correctly allows the name to be changed to the empty string.
- Fixed a crash in the Vector Merge SOP when fewer than three grids
  were merged.
- The From Particles SOP now features a "maximum half-width" parameter
  to help avoid runaway computations.


@htmlonly <a name="v0_102_0_changes"></a>@endhtmlonly
@par
<B>Version 0.102.0</B> - <I>December 13 2012</I>
- Added @vdblink::tools::compReplace() tools::compReplace@endlink,
  which copies the active values of one grid into another, and added
  a "Replace A With Active B" mode to the Combine SOP.
- @vdblink::Grid::signedFloodFill() Grid::signedFloodFill@endlink
  no longer enters an infinite loop when filling an empty grid.
- Fixed a bug in the particle to level set converter that sometimes
  produced level sets with holes, and fixed a bug in the SOP that
  could result in random output.
- Fixed an issue in the frustum preview feature of the Create SOP
  whereby rendering very large frustums could cause high CPU usage.
- Added streamline support to the constrained advection scheme
  in the Advect Points SOP.
- Added an Advect Level Set SOP.


@htmlonly <a name="v0_101_1_changes"></a>@endhtmlonly
@par
<B>Version 0.101.1</B> - <I>December 11 2012</I> (DWA internal release)
- Partially reverted the Houdini VDB primitive&rsquo;s grid accessor methods
  to their pre-0.98.0 behavior.  A primitive&rsquo;s grid can once again
  be accessed by shared pointer, but now also by reference.
  Accessor methods for grid metadata have also been added, and the
  primitive now ensures that metadata and transforms are never shared.
- Fixed an intermittent crash in the From Particles SOP.


@htmlonly <a name="v0_101_0_changes"></a>@endhtmlonly
@par
<B>Version 0.101.0</B> - <I>December 6 2012</I> (DWA internal release)
- Partially reverted the @vdblink::Grid Grid@endlink&rsquo;s
  @vdblink::Grid::tree() tree@endlink and
  @vdblink::Grid::transform() transform@endlink accessor methods
  to their pre-0.98.0 behavior, eliminating copy-on-write but
  preserving their return-by-reference semantics.  These methods
  are now supplemented with a suite of
  @vdblink::Grid::treePtr() shared@endlink
  @vdblink::Grid::baseTreePtr() pointer@endlink
  @vdblink::Grid::transformPtr() accessors@endlink.
- Restructured the @vdblink::tools::meshToVolume
  mesh to volume converter@endlink for a 40% speedup
  and to be more robust to non-manifold geometry, to better preserve
  sharp features, to support arbitrary tree configurations and
  to respect narrow-band limits.
- Added a @c getNodeBoundingBox method to
  @vdblink::tree::RootNode::getNodeBoundingBox() RootNode@endlink,
  @vdblink::tree::InternalNode::getNodeBoundingBox() InternalNode@endlink
  and @vdblink::tree::LeafNode::getNodeBoundingBox() LeafNode@endlink
  that returns the index space spanned by a node.
- Made various changes for Visual C++ compatibility.
  <I>[Contributed by SESI]</I>
- Renamed the Reshape Level Set SOP to Offset Level Set.
- Fixed a crash in the Convert SOP and added support for conversion
  of empty grids.


@htmlonly <a name="v0_100_0_changes"></a>@endhtmlonly
@par
<B>Version 0.100.0</B> - <I>November 30 2012</I> (DWA internal release)
- Greatly improved the performance of the level set to fog volume
  @vdblink::tools::sdfToFogVolume() converter@endlink.
- Improved the performance of the
  @vdblink::tools::Filter::median() median filter@endlink
  and of level set @vdblink::tools::csgUnion() CSG@endlink operations.
- Reintroduced Tree::pruneLevelSet(), a specialized Tree::pruneInactive()
  for level-set grids.
- Added utilities to the @c houdini_utils library to facilitate the
  collection of a chain of adjacent nodes of a particular type
  so that they can be cooked in a single step.  (For example,
  adjacent @c xform SOPs could be collapsed by composing their
  transformation matrices into a single matrix.)
- Added pruning and flood-filling options to the Convert SOP.
- Reimplemented the Filter SOP, omitting level-set-specific filters
  and adding node chaining (to reduce memory usage when applying
  several filters in sequence).
- Added a toggle to the Read SOP to read grid metadata and
  transforms only.
- Changed the attribute transfer scheme on the From Mesh and
  From Particles SOPs to allow for custom grid names and
  vector type metadata.


@htmlonly <a name="v0_99_0_changes"></a>@endhtmlonly
@par
<B>Version 0.99.0</B> - <I>November 21 2012</I>
- Added @vdblink::Grid Grid@endlink methods that return non-<TT>const</TT>
  tree and transform references without triggering deep copies,
  as well as @c const methods that return @c const shared pointers.
- Added @c Grid methods to @vdblink::Grid::addStatsMetadata populate@endlink
  a grid&rsquo;s metadata with statistics like the active voxel count, and to
  @vdblink::Grid::getStatsMetadata retrieve@endlink that metadata.
  By default, statistics are now computed and added to grids
  whenever they are written to <TT>.vdb</TT> files.
- Added @vdblink::io::File::readGridMetadata io::File::readGridMetadata@endlink
  and @vdblink::io::File::readAllGridMetadata
  io::File::readAllGridMetadata@endlink methods to read just the
  grid metadata and transforms from a <TT>.vdb</TT> file.
- Fixed numerical precision issues in the
  @vdblink::tools::csgUnion csgUnion@endlink,
  @vdblink::tools::csgIntersection csgIntersection@endlink
  and @vdblink::tools::csgDifference csgDifference@endlink
  tools, and added toggles to optionally disable postprocess pruning.
- Fixed an issue in @c vdb_view with the ordering of GL vertex buffer calls.
  <I>[Contributed by Bill Katz]</I>
- Fixed an intermittent crash in the
  @vdblink::tools::ParticlesToLevelSet ParticlesToLevelSet@endlink tool,
  as well as a race condition that could cause data corruption.
- The @c ParticlesToLevelSet tool and From Particles SOP can now transfer
  arbitrary point attribute values from the input particles to output voxels.
- Fixed a bug in the Convert SOP whereby the names of primitives
  were lost during conversion, and another bug that resulted in
  arithmetic errors when converting empty grids.
- Fixed a bug in the Combine SOP that caused the Operation selection
  to be lost.


@htmlonly <a name="v0_98_0_changes"></a>@endhtmlonly
@par
<B>Version 0.98.0</B> - <I>November 16 2012</I>
- @vdblink::tree::Tree Tree@endlink and
  @vdblink::math::Transform Transform@endlink objects (and
  @vdblink::Grid Grid@endlink objects in the context of Houdini SOPs)
  are now passed and accessed primarily by reference rather than by
  shared pointer.  See @subpage api_0_98_0 "Porting to OpenVDB 0.98.0"
  for details about this important API change.
  <I>[Contributed by SESI]</I>
- Reimplemented @vdblink::math::CoordBBox CoordBBox@endlink to address several
  off-by-one bugs related to bounding box dimensions.
- Fixed an off-by-one bug in @vdblink::Grid::evalActiveVoxelBoundingBox()
  evalActiveVoxelBoundingBox@endlink.
- Introduced the @vdblink::tree::LeafManager LeafManager@endlink class,
  which will eventually replace the @c LeafArray class.  @c LeafManager supports
  dynamic buffers stored as a structure of arrays (SOA), unlike @c LeafArray,
  which supports only static buffers stored as an array of structures (AOS).
- Improved the performance of the
  @vdblink::tools::LevelSetFilter LevelSetFilter@endlink and
  @vdblink::tools::LevelSetTracker LevelSetTracker@endlink tools by rewriting
  them to use the new @vdblink::tree::LeafManager LeafManager@endlink class.
- Added @vdblink::tree::Tree::setValueOnly() Tree::setValueOnly@endlink and
  @vdblink::tree::ValueAccessor::setValueOnly()
  ValueAccessor::setValueOnly@endlink methods, which change the value of
  a voxel without changing its active state, and
  @vdblink::tree::Tree::probeLeaf() Tree::probeLeaf@endlink and
  @vdblink::tree::ValueAccessor::probeLeaf() ValueAccessor::probeLeaf@endlink
  methods that return the leaf node that contains a given voxel (unless
  the voxel is represented by a tile).
- Added a @vdblink::tools::LevelSetAdvection LevelSetAdvection@endlink tool
  that propagates and tracks narrow-band level sets.
- Introduced a new @vdblink::tools::GridSampler GridSampler@endlink class
  that supports world-space (or index-space) sampling of grid values.
- Changed the interpretation of the
  @vdblink::math::NonlinearFrustumMap NonlinearFrustumMap@endlink&rsquo;s
  @em taper parameter to be the ratio of the near and far plane depths.
- Added a @c ParmFactory::setChoiceList() overload that accepts
  (@em token, @em label) string pairs, and a @c setDefault() overload that
  accepts an STL string.
- Fixed a crash in the Combine SOP in Copy B mode.
- Split the Level Set Filter SOP into three separate SOPs,
  Level Set Smooth, Level Set Reshape and Level Set Renormalize.
  When two or more of these nodes are connected in sequence, they interact
  to reduce memory usage: the last node in the sequence performs
  all of the operations in one step.
- The Advect Points SOP can now output polyline streamlines
  that trace the paths of the points.
- Added an option to the Analysis SOP to specify names for output grids.
- Added camera-derived frustum transform support to the Create SOP.


@htmlonly <a name="v0_97_0_changes"></a>@endhtmlonly
@par
<B>Version 0.97.0</B> - <I>October 18 2012</I>
- Added a narrow-band @vdblink::tools::LevelSetTracker level set
  interface tracking tool@endlink (up to fifth-order in space but currently
  only first-order in time, with higher temporal orders to be added soon).
- Added a @vdblink::tools::LevelSetFilter level set filter tool@endlink
  to perform unrestricted surface smoothing (e.g., Laplacian flow),
  filtering (e.g., mean value) and morphological operations (e.g.,
  morphological opening).
- Added adaptivity to the @vdblink::tools::VolumeToMesh
  level set meshing tool@endlink for faster mesh extraction with fewer
  polygons, without postprocessing.
- Added a @vdblink::tree::ValueAccessor::touchLeaf()
  ValueAccessor::touchLeaf@endlink method that creates (if necessary)
  and returns the leaf node containing a given voxel.  It can be used
  to preallocate leaf nodes over which to run parallel algorithms.
- Fixed a bug in @vdblink::Grid::merge() Grid::merge@endlink whereby
  active tiles were sometimes lost.
- Added @vdblink::tree::LeafManager LeafManager@endlink, which is similar
  to @c LeafArray but supports a dynamic buffer count and allocates buffers
  more efficiently.  Useful for temporal integration (e.g., for level set
  propagation and interface tracking), @c LeafManager is meant to replace
  @c LeafArray, which will be deprecated in the next release.
- Added a @vdblink::tree::LeafNode::fill() LeafNode::fill@endlink method
  to efficiently populate leaf nodes with constant values.
- Added a @vdblink::tree::Tree::visitActiveBBox() Tree::visitActiveBBox@endlink
  method that applies a functor to the bounding boxes of all active tiles
  and leaf nodes and that can be used to improve the performance of
  ray intersection tests, rendering of bounding boxes, etc.
- Added a @vdblink::tree::Tree::voxelizeActiveTiles()
  Tree::voxelizeActiveTiles@endlink method to densify active tiles.
  While convenient and fast, this can produce large dense grids, so use
  it with caution.
- Repackaged @c Tree::pruneLevelSet() as a Tree::pruneOp()-compatible
  functor.  Tree::LevelSetPrune is a specialized Tree::pruneInactive
  for level-set grids and is used in interface tracking.
- Added a GridBase::pruneGrid() method.
- Added a @vdblink::Grid::hasUniformVoxels() Grid:hasUniformVoxels@endlink
  method.
- Renamed @c tools::dilate to
  @vdblink::tools::dilateVoxels() dilateVoxels@endlink and improved its
  performance.  The new name reflects the fact that the current
  implementation ignores active tiles.
- Added a @vdblink::tools::resampleToMatch() tools::resampleToMatch@endlink
  function that resamples an input grid into an output grid with a
  different transform such that, after resampling, the input and output grids
  coincide, but the output grid&rsquo;s transform is preserved.
- Significantly improved the performance of depth-bounded value
  iterators (@vdblink::tree::Tree::ValueOnIter ValueOnIter@endlink,
  @vdblink::tree::Tree::ValueAllIter ValueAllIter@endlink, etc.)
  when the depth bound excludes leaf nodes.
- Exposed the value buffers inside leaf nodes with
  @vdblink::tree::LeafNode::buffer() LeafNode::buffer@endlink.
  This allows for very fast access (const and non-const) to voxel
  values using linear array offsets instead of @ijk coordinates.
- In openvdb_houdini/UT_VDBTools.h, added operators for use with
  @c processTypedGrid that resample grids in several different ways.
- Added a policy mechanism to @c houdini_utils::OpFactory that allows for
  customization of operator names, icons, and Help URLs.
- Renamed many of the Houdini SOPs to make the names more consistent.
- Added an Advect Points SOP.
- Added a Level Set Filter SOP that allows for unrestricted surface
  deformations, unlike the older Filter SOP, which restricts surface
  motion to the initial narrow band.
- Added staggered vector sampling to the Sample Points SOP.
- Added a minimum radius threshold to the particle voxelization tool
  and SOP.
- Merged the Composite and CSG SOPs into a single Combine SOP.
- Added a tool and a SOP to efficiently generate narrow-band level set
  representations of spheres.
- In the Visualize SOP, improved the performance of tree topology
  generation, which is now enabled by default.


@htmlonly <a name="v0_96_0_changes"></a>@endhtmlonly
@par
<B>Version 0.96.0</B> - <I>September 24 2012</I>
- Fixed a memory corruption bug in the mesh voxelizer tool.
- Temporarily removed the optional clipping feature from the level set mesher.
- Added "Staggered Vector Field" to the list of grid classes in the Create SOP.


@htmlonly <a name="v0_95_0_changes"></a>@endhtmlonly
@par
<B>Version 0.95.0</B> - <I>September 20 2012</I>
- Added a quad @vdblink::tools::VolumeToMesh meshing@endlink tool for
  higher-quality level set meshing and updated the Visualizer SOP
  to use it.
- Fixed a precision error in the @vdblink::tools::meshToVolume
  mesh voxelizer@endlink and improved the quality of inside/outside
  voxel classification.  Output grids are now also
  @vdblink::Grid::setGridClass() classified@endlink as either level sets
  or fog volumes.
- Modified the @vdblink::tools::GridResampler GridResampler@endlink
  to use the signed flood fill optimization only on grids that are
  tagged as level sets.
- Added a @vdblink::math::Quat quaternion@endlink class to the
  math library and a method to return the
  @vdblink::math::Mat3::trace trace@endlink of a @c Mat3.
- Fixed a bug in the
  @vdblink::tree::ValueAccessor::ValueAccessor(const ValueAccessor&)
  ValueAccessor@endlink copy constructor that caused the copy to reference
  the original.
- Fixed a bug in @vdblink::tree::RootNode::setActiveState()
  RootNode::setActiveState@endlink that caused a crash
  when marking a (virtual) background voxel as inactive.
- Added a @c Tree::pruneLevelSet method that is similar to but faster than
  Tree::pruneInactive() for level set grids.
- Added fast leaf node voxel access
  @vdblink::tree::LeafNode::getValue(Index) const methods@endlink
  that index by linear offset (as returned by
  @vdblink::tree::LeafNode::ValueOnIter::pos() ValueIter::pos@endlink)
  instead of by @ijk coordinates.
- Added a @vdblink::tree::Tree::touchLeaf() Tree::touchLeaf@endlink
  method that can be used to preallocate a static tree topology over which
  to safely perform multithreaded processing.
- Added a grain size argument to @c LeafArray for finer control of parallelism.
- Modified the Makefile to make it easier to omit the <TT>doc</TT>,
  @c vdb_test and @c vdb_view targets.
- Added utility functions (in <TT>houdini/UT_VDBUtils.h</TT>) to convert
  between Houdini and OpenVDB matrix and vector types.
  <I>[Contributed by SESI]</I>
- Added accessors to @c GEO_PrimVDB that make it easier to directly access
  voxel data and that are used by the HScript volume expression functions
  in Houdini 12.5.  <I>[Contributed by SESI]</I>
- As of Houdini 12.1.77, the native transform SOP operates on OpenVDB
  primitives.  <I>[Contributed by SESI]</I>
- Added a Convert SOP that converts OpenVDB grids to Houdini volumes
  and vice-versa.


@htmlonly <a name="v0_94_1_changes"></a>@endhtmlonly
@par
<B>Version 0.94.1</B> - <I>September 7 2012</I>
- Fixed bugs in @vdblink::tree::RootNode RootNode@endlink and
  @vdblink::tree::InternalNode InternalNode@endlink @c setValue*() and
  @c fill() methods that could cause neighboring voxels to become inactive.
- Fixed a bug in
  @vdblink::tree::Tree::hasSameTopology() Tree::hasSameTopology@endlink
  that caused false positives when only active states and not values differed.
- Added a @vdblink::tree::Tree::hasActiveTiles() Tree::hasActiveTiles@endlink
  method.
- For better cross-platform consistency, substituted bitwise AND operations
  for right shifts in the @vdblink::tree::ValueAccessor ValueAccessor@endlink
  hash key computation.
- @c vdb_view no longer aborts when asked to surface a vector-valued
  grid&mdash;but it still doesn&rsquo;t render the surface.
- Made various changes for Visual C++ compatibility.
  <I>[Contributed by SESI]</I>
- Added an option to the MeshVoxelizer SOP to convert both open and
  closed surfaces to unsigned distance fields.
- The Filter SOP now allows multiple filters to be applied in
  user-specified order.


@htmlonly <a name="v0_94_0_changes"></a>@endhtmlonly
@par
<B>Version 0.94.0</B> - <I>August 30 2012</I>
- Added a @vdblink::Grid::topologyUnion() method@endlink to union
  just the active states of voxels from one grid with those of
  another grid of a possibly different type.
- Fixed an incorrect scale factor in the Laplacian diffusion
  @vdblink::tools::Filter::laplacian() filter@endlink.
- Fixed a bug in @vdblink::tree::Tree::merge() Tree::merge@endlink
  that could leave a tree with invalid value accessors.
- Added @vdblink::tree::TreeValueIteratorBase::setActiveState()
  TreeValueIteratorBase::setActiveState@endlink and deprecated
  @c setValueOn.
- Removed @c tools/FastSweeping.h.  It will be replaced with a much more
  efficient implementation in the near future.
- ZLIB compression of <TT>.vdb</TT> files is now optional,
  but enabled by default.  <I>[Contributed by SESI]</I>
- Made various changes for Clang and Visual C++ compatibility.
  <I>[Contributed by SESI]</I>
- The MeshVoxelizer SOP can now transfer arbitrary point and primitive
  attribute values from the input mesh to output voxels.


@htmlonly <a name="v0_93_0_changes"></a>@endhtmlonly
@par
<B>Version 0.93.0</B> - <I>August 24 2012</I>
- Renamed symbols in math/Operators.h to avoid ambiguities that
  GCC&nbsp;4.4 reports as errors.
- Simplified the API for the stencil version of the
  closest-point transform @vdblink::math::CPT operator@endlink.
- Added logic to
  @vdblink::io::Archive::readGrid() io::Archive::readGrid@endlink
  to set the grid name metadata from the descriptor if the metadata
  doesn&rsquo;t already exist.
- Added guards to prevent nesting of @c openvdb_houdini::Interrupter::start()
  and @c end() calls.


@htmlonly <a name="v0_92_0_changes"></a>@endhtmlonly
@par
<B>Version 0.92.0</B> - <I>August 23 2012</I>
- Added a Laplacian diffusion
  @vdblink::tools::Filter::laplacian() filter@endlink.
- Fixed a bug in the initialization of the sparse contour tracer
  that caused mesh-to-volume conversion to fail in certain cases.
- Fixed a bug in the curvature stencil that caused mean curvature
  filtering to produce wrong results.
- Increased the speed of the
  @vdblink::tools::GridTransformer GridTransformer@endlink
  by as much as 20% for fog volumes.
- Added optional pruning to the Resample SOP.
- Modified the PointSample SOP to allow it to work with ungrouped,
  anonymous grids.
- Fixed a crash in the LevelSetNoise SOP.


@htmlonly <a name="v0_91_0_changes"></a>@endhtmlonly
@par
<B>Version 0.91.0</B> - <I>August 16 2012</I>
- @vdblink::tools::GridTransformer tools::GridTransformer@endlink
  and @vdblink::tools::GridResampler tools::GridResampler@endlink
  now correctly (but not yet efficiently) process tiles in sparse grids.
- Added an optional @vdblink::CopyPolicy CopyPolicy@endlink argument
  to @vdblink::GridBase::copyGrid() GridBase::copyGrid@endlink
  and to @vdblink::Grid::copy() Grid::copy@endlink that specifies
  whether and how the grid&rsquo;s tree should be copied.
- Added a @vdblink::GridBase::newTree() GridBase::newTree@endlink
  method that replaces a grid&rsquo;s tree with a new, empty tree of the
  correct type.
- Fixed a crash in
  @vdblink::tree::Tree::setValueOff(const Coord& xyz, const ValueType& value)
  Tree::setValueOff@endlink when the new value was equal to the
  background value.
- Fixed bugs in Tree::prune() that could result in output tiles with
  incorrect active states.
- Added @c librt to the link dependencies to address build failures
  on Ubuntu systems.
- Made various small changes to the Makefile and the source code
  that should help with Mac OS&nbsp;X compatibility.
- The Composite and Resample SOPs now correctly copy the input grid&rsquo;s
  metadata to the output grid.


@htmlonly <a name="v0_90_1_changes"></a>@endhtmlonly
@par
<B>Version 0.90.1</B> - <I>August 7 2012</I>
- Fixed a bug in the
  @vdblink::math::BBox::getCenter() BBox::getCenter()@endlink method.
- Added missing header files to various files.
- @vdblink::io::File::NameIterator::gridName()
  io::File::NameIterator::gridName()@endlink now returns a unique name
  of the form <TT>"name[1]"</TT>, <TT>"name[2]"</TT>, etc. if a file
  contains multiple grids with the same name.
- Fixed a bug in the Writer SOP that caused grid names to be discarded.
- The Resample SOP now correctly sets the background value of the
  output grid.


@htmlonly <a name="v0_90_0_changes"></a>@endhtmlonly
@par
<B>Version 0.90.0</B> - <I>August 3 2012</I> (initial public release)
- Added a basic GL viewer for OpenVDB files.
- Greatly improved the performance of two commonly-used @c Tree methods,
  @vdblink::tree::Tree::evalActiveVoxelBoundingBox()
  evalActiveVoxelBoundingBox()@endlink
  and @vdblink::tree::Tree::memUsage() memUsage()@endlink.
- Eliminated the @c GridMap class.  File I/O now uses STL containers
  of grid pointers instead.
- Refactored stencil-based tools (Gradient, Laplacian, etc.) and rewrote
  some of them for generality and better performance.  Most now behave
  correctly for grids with nonlinear index-to-world transforms.
- Added a @link FiniteDifference.h library@endlink of index-space finite
  difference operators.
- Added a Hermite grid type that compactly
  stores each voxel&rsquo;s upwind normals and can be used to convert volumes
  to and from polygonal meshes.
- Added a @link PointScatter.h tool@endlink (and a Houdini SOP)
  to scatter points randomly throughout a volume.

*/
