This is release v0.9.0 of Intel® Open VKL. For changes and new features see the changelog. Visit http://www.openvkl.org for more information.
Intel® Open Volume Kernel Library (Intel® Open VKL) is a collection of high-performance volume computation kernels, developed at Intel. The target users of Open VKL are graphics application engineers who want to improve the performance of their volume rendering applications by leveraging Open VKL’s performance-optimized kernels, which include volume traversal and sampling functionality for a variety of volumetric data formats. The kernels are optimized for the latest Intel® processors with support for SSE, AVX, AVX2, and AVX-512 instructions. Open VKL is part of the Intel® oneAPI Rendering Toolkit and is released under the permissive Apache 2.0 license.
Open VKL provides a C API, and also supports applications written with the Intel® SPMD Program Compiler (ISPC) by also providing an ISPC interface to the core volume algorithms. This makes it possible to write a renderer in ISPC that automatically vectorizes and leverages SSE, AVX, AVX2, and AVX-512 instructions. ISPC also supports runtime code selection, thus ISPC will select the best code path for your application.
In addition to the volume kernels, Open VKL provides tutorials and example renderers to demonstrate how to best use the Open VKL API.
- Added support for VDB sparse structured volumes (
"vdb"volume type) - Added
vdb_utillibrary to simplify instantiation of VDB volumes, and support loading of .vdb files using OpenVDB - Added
VKLObserverand associated APIs, which may used by volume types to pass information back to the application- A
LeafNodeAccessobserver is provided for VDB volumes to support on-demand loading of leaf nodes
- A
- Structured regular volumes:
- Up to 6x performance improvement for scalar iterator initialization
- Up to 2x performance improvement for scalar iterator iteration
- General improvements to the CMake Superbuild for building Open VKL and all associated dependencies
- Allowing instantiation of ISPC driver for any supported SIMD width (in addition to the default automatically selected width)
- Volume type names are now camelCase (legacy snake_case type names
are deprecated), impacting
structuredRegularandstructuredSphericalvolumes - Enabling
flushDenormalsdriver mode by default - Aligning public
vkl_vvec3f[4,8,16]andvkl_vrange1f[4,8,16]types - Added
VKL_LOG_NONElog level - Fixed bug in
vklExampleswhich could lead to improper rendering on macOS Catalina - Fixed bug in unstructured volume interval iterator which could lead to errors with some combinations of lane masks
- Now providing binary releases for Linux, macOS, and Windows
- Added support for structured volumes on spherical grids
(
"structured_spherical"volume type) - Structured regular volumes:
- Up to 8x performance improvement for scalar (single-wide) sampling
- Fixed hit iterator bug which could lead to isosurfacing artifacts
- Renamed
voxelDataparameter todata
- Unstructured volumes:
- Up to 4x performance improvement for scalar (single-wide) sampling
- Improved interval iterator implementation for more efficient space skipping and tighter value bounds on returned intervals
- Now using Embree for BVH builds for faster build times / volume commits
- Renamed
vertex.valueandcell.valueparameters tovertex.dataandcell.data, respectively
- AMR volumes:
- renamed
block.cellWidthparameter tocellWidth, and clarified API documentation
- renamed
- Added
vklGetValueRange()API for querying volume value ranges - Added new driver parameters, APIs, and environment variables allowing user control of log levels, log / error output redirection, number of threads, and other options
vklIterateHit[4,8,16]()andvklIterateInterval[4,8,16]()calls now only populate hit / interval data for active lanes- Changed
VKLDataTypeenum values for better forward compatibility - ISPC-side hit and interval iterator objects must now be declared
varying - More flexible ISA build configuration through
OPENVKL_MAX_ISAandOPENVKL_ISA_*CMake build options - Minimum ospcommon version is now 1.1.0
- Initial public alpha release, with support for structured, unstructured, and AMR volumes.
Open VKL is under active development, and though we do our best to guarantee stable release versions a certain number of bugs, as-yet-missing features, inconsistencies, or any other issues are still possible. Should you find any such issues please report them immediately via Open VKL’s GitHub Issue Tracker (or, if you should happen to have a fix for it, you can also send us a pull request); you may also contact us via email at [email protected].
Join our mailing list to receive release announcements and major news regarding Open VKL.
To access the Open VKL API you first need to include the Open VKL header. For C99 or C++:
#include <openvkl/openvkl.h>For the Intel SPMD Program Compiler (ISPC):
#include <openvkl/openvkl.isph>This documentation will discuss the C99/C++ API. The ISPC version has
the same functionality and flavor. Looking at the headers, the
vklTutorialISPC example, and this documentation should be enough to
figure it out.
To use the API, one of the implemented backends must be loaded. Currently the only one that exists is the ISPC driver. ISPC in the name here just refers to the implementation language – it can also be used from the C99/C++ APIs. To load the module that implements the ISPC driver:
vklLoadModule("ispc_driver");The driver then needs to be instantiated:
VKLDriver driver = vklNewDriver("ispc");By default, the ISPC driver selects the maximum supported SIMD width
(and associated ISA) for the system. Optionally, a specific width may be
requested using the ispc_4, ispc_8, or ispc_16 driver names. Note
that the system must support the given width (SSE4.1 for 4-wide, AVX for
8-wide, and AVX512 for 16-wide).
Once a driver is created, you can call
void vklDriverSetInt(VKLDriver, const char *name, int val);
void vklDriverSetString(VKLDriver, const char *name, const char *val);to set parameters on the driver. The following parameters are understood by all drivers:
| Type | Name | Description |
|---|---|---|
| int | logLevel | logging level; valid values are VKL_LOG_DEBUG, VKL_LOG_INFO, VKL_LOG_WARNING, VKL_LOG_ERROR and VKL_LOG_NONE |
| string | logOutput | convenience for setting where log messages go; valid values are cout, cerr and none |
| string | errorOutput | convenience for setting where error messages go; valid values are cout, cerr and none |
| int | numThreads | number of threads which Open VKL can use |
| int | flushDenormals | sets the Flush to Zero and Denormals are Zero mode of the MXCSR control and status register (default: 1); see Performance Recommendations section for details |
Parameters shared by all drivers.
Once parameters are set, the driver must be committed with
vklCommitDriver(driver);Finally, to use the newly committed driver, you must call
vklSetCurrentDriver(driver);Users can change parameters on a driver after initialization. In this case the driver would need to be re-committed. If changes are made to the driver that is already set as the current driver, it does not need to be set as current again. The currently set driver can be retrieved at any time by calling
VKLDriver driver = vklGetCurrentDriver();Open VKL provides vector-wide versions for several APIs. To determine the native vector width for the given driver, call:
int width = vklGetNativeSIMDWidth();When the application is finished with Open VKL or shutting down, call the shutdown function:
vklShutdown();The generic driver parameters can be overridden via environment
variables for easy changes to Open VKL’s behavior without needing to
change the application (variables are prefixed by convention with
“OPENVKL_”):
| Variable | Description |
|---|---|
| OPENVKL_LOG_LEVEL | logging level; valid values are debug, info, warning, error and none |
| OPENVKL_LOG_OUTPUT | convenience for setting where log messages go; valid values are cout, cerr and none |
| OPENVKL_ERROR_OUTPUT | convenience for setting where error messages go; valid values are cout, cerr and none |
| OPENVKL_THREADS | number of threads which Open VKL can use |
| OPENVKL_FLUSH_DENORMALS | sets the Flush to Zero and Denormals are Zero mode of the MXCSR control and status register (default: 1); see Performance Recommendations section for details |
Environment variables understood by all drivers.
Note that these environment variables take precedence over values set
through the vklDriverSet*() functions.
The following errors are currently used by Open VKL:
| Name | Description |
|---|---|
| VKL_NO_ERROR | no error occurred |
| VKL_UNKNOWN_ERROR | an unknown error occurred |
| VKL_INVALID_ARGUMENT | an invalid argument was specified |
| VKL_INVALID_OPERATION | the operation is not allowed for the specified object |
| VKL_OUT_OF_MEMORY | there is not enough memory to execute the command |
| VKL_UNSUPPORTED_CPU | the CPU is not supported (minimum ISA is SSE4.1) |
Possible error codes, i.e., valid named constants of type VKLError.
These error codes are either directly returned by some API functions, or are recorded to be later queried by the application via
VKLError vklDriverGetLastErrorCode(VKLDriver);A more descriptive error message can be queried by calling
const char* vklDriverGetLastErrorMsg(VKLDriver);Alternatively, the application can also register a callback function of type
typedef void (*VKLErrorFunc)(VKLError, const char* message);via
void vklDriverSetErrorFunc(VKLDriver, VKLErrorFunc);to get notified when errors occur. Applications may be interested in messages which Open VKL emits, whether for debugging or logging events. Applications can register a callback function of type
typedef void (*VKLLogFunc)(const char* message);via
void vklDriverSetLogFunc(VKLDriver, VKLLogFunc);which Open VKL will use to emit log messages. Applications can clear
either callback by passing nullptr instead of an actual function
pointer. By default, Open VKL uses cout and cerr to emit log and
error messages, respectively. Note that in addition to setting the above
callbacks, this behavior can be changed via the driver parameters and
environment variables described previously.
Open VKL defines 3-component vectors of integer and vector types:
typedef struct
{
int x, y, z;
} vkl_vec3i;
typedef struct
{
float x, y, z;
} vkl_vec3f;Vector versions of these are also defined in structure-of-array format for 4, 8, and 16 wide types.
typedef struct
{
float x[WIDTH];
float y[WIDTH];
float z[WIDTH];
} vkl_vvec3f##WIDTH;
typedef struct
{
float lower[WIDTH], upper[WIDTH];
} vkl_vrange1f##WIDTH;1-D range and 3-D ranges are defined as ranges and boxes, with no vector versions:
typedef struct
{
float lower, upper;
} vkl_range1f;
typedef struct
{
vkl_vec3f lower, upper;
} vkl_box3f;Objects in Open VKL are exposed to the APIs as handles with internal
reference counting for lifetime determination. Objects are created with
particular type’s vklNew... API entry point. For example, vklNewData
and vklNewVolume.
In general, modifiable parameters to objects are modified using
vklSet... functions based on the type of the parameter being set. The
parameter name is passed as a string. Below are all variants of
vklSet....
void vklSetBool(VKLObject object, const char *name, int b);
void vklSetFloat(VKLObject object, const char *name, float x);
void vklSetVec3f(VKLObject object, const char *name, float x, float y, float z);
void vklSetInt(VKLObject object, const char *name, int x);
void vklSetVec3i(VKLObject object, const char *name, int x, int y, int z);
void vklSetData(VKLObject object, const char *name, VKLData data);
void vklSetString(VKLObject object, const char *name, const char *s);
void vklSetVoidPtr(VKLObject object, const char *name, void *v);The exception to this rule is the VKLValueSelector object (described
in the iterators section below), which has object-specific set methods.
The reason for this is to align the C99/C++ API with the ISPC API, which
can’t use a parameter method due to language limitations.
After parameters have been set, vklCommit must be called on the object
to make them take effect.
Open VKL uses reference counting to manage the lifetime of all objects. Therefore one cannot explicitly “delete” any object. Instead, one can indicate the application does not need or will not access the given object anymore by calling
void vklRelease(VKLObject);This decreases the object’s reference count. If the count reaches 0
the object will automatically be deleted.
Large data is passed to Open VKL via a VKLData handle created with
vklNewData:
VKLData vklNewData(size_t numItems,
VKLDataType dataType,
const void *source,
VKLDataCreationFlags dataCreationFlags);Types accepted are listed in VKLDataType.h; basic types (UCHAR,
INT, UINT, LONG, ULONG) exist as both scalar and chunked
formats. The types accepted vary per volume at the moment; read the
volume section below for specifics.
Data objects can be created as Open VKL owned (dataCreationFlags = VKL_DATA_DEFAULT), in which the library will make a copy of the data
for its use, or shared (dataCreationFlags = VKL_DATA_SHARED_BUFFER),
which will try to use the passed pointer for usage. The library is
allowed to copy data when a volume is committed.
As with other object types, when data objects are no longer needed they
should be released via vklRelease.
Volumes in Open VKL may provide observers to communicate data back to the application. Observers may be created with
VKLObserver vklNewObserver(VKLVolume volume,
const char *type);The volume passed to vklNewObserver must already be committed. Valid
observer type strings are defined by volume implementations (see section
‘Volume types’ below).
vklNewObserver returns NULL on failure.
To access the underlying data, an observer must first be mapped using
const void * vklMapObserver(VKLObserver observer);If this fails, the function returns NULL. vklMapObserver may fail on
observers that are already mapped. On success, the application may query
the underlying type and the number of elements in the buffer using
VKLDataType vklGetObserverElementType(VKLObserver observer);
size_t vklGetObserverNumElements(VKLObserver observer);On failure, these functions return VKL_UNKNOWN and 0, respectively.
Possible data types are defined by the volume that provides the observer
, as are the semantics of the observation. See section ‘Volume types’
for details.
The pointer returned by vklMapObserver may be cast to the type
corresponding to the value returned by vklGetObserverElementType to
access the observation. For example, if vklGetObserverElementType
returns VKL_FLOAT, then the pointer returned by vklMapObserver may
be cast to const float * to access up to vklGetObserverNumElements
consecutive values of type float.
Once the application has finished processing the observation, it should unmap the observer using
void vklUnmapObserver(VKLObserver observer);so that the observer may be mapped again.
When an observer is no longer needed, it should be released using
vklRelease.
The observer API is not thread safe, and these functions should not be called concurrently on the same object.
Open VKL currently supports structured volumes on regular and spherical
grids; unstructured volumes with tetrahedral, wedge, pyramid, and
hexaderal primitive types; and adaptive mesh refinement (AMR) volumes.
These volumes are created with vklNewVolume with the appropriate type
string.
In addition to the usual vklSet...() and vklCommit() APIs, the
volume bounding box can be queried:
vkl_box3f vklGetBoundingBox(VKLVolume volume);The value range of the volume can also be queried:
vkl_range1f vklGetValueRange(VKLVolume volume);Structured volumes only need to store the values of the samples, because their addresses in memory can be easily computed from a 3D position. The dimensions for all structured volume types are in units of vertices, not cells. For example, a volume with dimensions ((x, y, z)) will have ((x-1, y-1, z-1)) cells in each dimension. Voxel data provided is assumed vertex-centered, so (xyz) values must be provided.
A common type of structured volumes are regular grids, which are created
by passing a type string of "structuredRegular" to vklNewVolume. The
parameters understood by structured regular volumes are summarized in
the table below.
| Type | Name | Default | Description |
|---|---|---|---|
| vec3i | dimensions | number of voxels in each dimension ((x, y, z)) | |
| data | data | VKLData object of voxel data, supported types are: | |
VKL_UCHAR |
|||
VKL_SHORT |
|||
VKL_USHORT |
|||
VKL_FLOAT |
|||
VKL_DOUBLE |
|||
| vec3f | gridOrigin | ((0, 0, 0)) | origin of the grid in world-space |
| vec3f | gridSpacing | ((1, 1, 1)) | size of the grid cells in world-space |
Configuration parameters for structured regular ("structuredRegular")
volumes.
Structured spherical volumes are also supported, which are created by
passing a type string of "structuredSpherical" to vklNewVolume. The
grid dimensions and parameters are defined in terms of radial distance
((r)), inclination angle ((\theta)), and azimuthal angle ((\phi)),
conforming with the ISO convention for spherical coordinate systems. The
coordinate system and parameters understood by structured spherical
volumes are summarized below.
[Structured spherical volume coordinate system: radial distance ((r)), inclination angle ((\theta)), and azimuthal angle ((\phi)).][imgStructuredSphericalCoords]
| Type | Name | Default | Description |
|---|---|---|---|
| vec3i | dimensions | number of voxels in each dimension ((r, \theta, \phi)) | |
| data | data | VKLData object of voxel data, supported types are: | |
VKL_UCHAR |
|||
VKL_SHORT |
|||
VKL_USHORT |
|||
VKL_FLOAT |
|||
VKL_DOUBLE |
|||
| vec3f | gridOrigin | ((0, 0, 0)) | origin of the grid in units of ((r, \theta, \phi)); angles in degrees |
| vec3f | gridSpacing | ((1, 1, 1)) | size of the grid cells in units of ((r, \theta, \phi)); angles in degrees |
Configuration parameters for structured spherical
("structuredSpherical") volumes.
These grid parameters support flexible specification of spheres, hemispheres, spherical shells, spherical wedges, and so forth. The grid extents (computed as ([gridOrigin, gridOrigin + (dimensions - 1) * gridSpacing])) however must be constrained such that:
- (r \geq 0)
- (0 \leq \theta \leq 180)
- (0 \leq \phi \leq 360)
Open VKL currently supports block-structured (Berger-Colella) AMR volumes. Volumes are specified as a list of blocks, which exist at levels of refinement in potentially overlapping regions. Blocks exist in a tree structure, with coarser refinement level blocks containing finer blocks. The cell width is equal for all blocks at the same refinement level, though blocks at a coarser level have a larger cell width than finer levels.
There can be any number of refinement levels and any number of blocks at
any level of refinement. An AMR volume type is created by passing the
type string "amr" to vklNewVolume.
Blocks are defined by three parameters: their bounds, the refinement level in which they reside, and the scalar data contained within each block.
Note that cell widths are defined per refinement level, not per block.
| Type | Name | Default | Description |
|---|---|---|---|
VKLAMRMethod |
method | VKL_AMR_CURRENT |
VKLAMRMethod sampling method. Supported methods are: |
VKL_AMR_CURRENT |
|||
VKL_AMR_FINEST |
|||
VKL_AMR_OCTANT |
|||
| float[] | cellWidth | NULL | array of each level’s cell width |
| box3f[] | block.bounds | NULL | [data] array of bounds for each AMR block |
| int[] | block.level | NULL | array of each block’s refinement level |
| VKLData[] | block.data | NULL | [data] array of VKLData containing the actual scalar voxel data |
| vec3f | gridOrigin | ((0, 0, 0)) | origin of the grid in world-space |
| vec3f | gridSpacing | ((1, 1, 1)) | size of the grid cells in world-space |
Configuration parameters for AMR ("amr") volumes.
Lastly, note that the gridOrigin and gridSpacing parameters act just
like the structured volume equivalent, but they only modify the root
(coarsest level) of refinement.
In particular, Open VKL’s AMR implementation was designed to cover
Berger-Colella [1] and Chombo [2] AMR data. The method parameter
above determines the interpolation method used when sampling the volume.
VKL_AMR_CURRENTfinds the finest refinement level at that cell and interpolates through this “current” levelVKL_AMR_FINESTwill interpolate at the closest existing cell in the volume-wide finest refinement level regardless of the sample cell’s levelVKL_AMR_OCTANTinterpolates through all available refinement levels at that cell. This method avoids discontinuities at refinement level boundaries at the cost of performance
Details and more information can be found in the publication for the implementation [3].
- M. J. Berger, and P. Colella. “Local adaptive mesh refinement for shock hydrodynamics.” Journal of Computational Physics 82.1 (1989): 64-84. DOI: 10.1016/0021-9991(89)90035-1
- M. Adams, P. Colella, D. T. Graves, J.N. Johnson, N.D. Keen, T. J. Ligocki. D. F. Martin. P.W. McCorquodale, D. Modiano. P.O. Schwartz, T.D. Sternberg and B. Van Straalen, Chombo Software Package for AMR Applications - Design Document, Lawrence Berkeley National Laboratory Technical Report LBNL-6616E.
- I. Wald, C. Brownlee, W. Usher, and A. Knoll. CPU volume rendering of adaptive mesh refinement data. SIGGRAPH Asia 2017 Symposium on Visualization on - SA ’17, 18(8), 1–8. DOI: 10.1145/3139295.3139305
Unstructured volumes can have their topology and geometry freely
defined. Geometry can be composed of tetrahedral, hexahedral, wedge or
pyramid cell types. The data format used is compatible with VTK and
consists of multiple arrays: vertex positions and values, vertex
indices, cell start indices, cell types, and cell values. An
unstructured volume type is created by passing the type string
"unstructured" to vklNewVolume.
Sampled cell values can be specified either per-vertex (vertex.data)
or per-cell (cell.data). If both arrays are set, cell.data takes
precedence.
Similar to a mesh, each cell is formed by a group of indices into the
vertices. For each vertex, the corresponding (by array index) data value
will be used for sampling when rendering, if specified. The index order
for a tetrahedron is the same as VTK_TETRA: bottom triangle
counterclockwise, then the top vertex.
For hexahedral cells, each hexahedron is formed by a group of eight
indices into the vertices and data values. Vertex ordering is the same
as VTK_HEXAHEDRON: four bottom vertices counterclockwise, then top
four counterclockwise.
For wedge cells, each wedge is formed by a group of six indices into the
vertices and data values. Vertex ordering is the same as VTK_WEDGE:
three bottom vertices counterclockwise, then top three counterclockwise.
For pyramid cells, each cell is formed by a group of five indices into
the vertices and data values. Vertex ordering is the same as
VTK_PYRAMID: four bottom vertices counterclockwise, then the top
vertex.
To maintain VTK data compatibility an index array may be specified via
the indexPrefixed array that allows vertex indices to be interleaved
with cell sizes in the following format:
(n, id_1, ..., id_n, m, id_1, ..., id_m).
| Type | Name | Default | Description |
|---|---|---|---|
| vec3f[] | vertex.position | [data] array of vertex positions | |
| float[] | vertex.data | [data] array of vertex data values to be sampled | |
| uint32[] / uint64[] | index | [data] array of indices (into the vertex array(s)) that form cells | |
| uint32[] / uint64[] | indexPrefixed | alternative [data] array of indices compatible to VTK, where the indices of each cell are prefixed with the number of vertices | |
| uint32[] / uint64[] | cell.index | [data] array of locations (into the index array), specifying the first index of each cell | |
| float[] | cell.data | [data] array of cell data values to be sampled | |
| uint8[] | cell.type | [data] array of cell types (VTK compatible). Supported types are: | |
VKL_TETRAHEDRON |
|||
VKL_HEXAHEDRON |
|||
VKL_WEDGE |
|||
VKL_PYRAMID |
|||
| bool | hexIterative | false | hexahedron interpolation method, defaults to fast non-iterative version which could have rendering inaccuracies may appear if hex is not parallelepiped |
| bool | precomputedNormals | false | whether to accelerate by precomputing, at a cost of 12 bytes/face |
Configuration parameters for unstructured ("unstructured") volumes.
VDB volumes implement a data structure that is very similar to the data structure outlined in Museth [1].
The data structure is a hierarchical regular grid at its core: Nodes are regular grids, and each grid cell may either store a constant value (this is called a tile), or child pointers.
Nodes in VDB trees are wide: Nodes on the first level have a resolution of 32^3 voxels by default, on the next level 16^3, and on the leaf level 8^3 voxels. All nodes on a given level have the same resolution. This makes it easy to find the node containing a coordinate using shift operations (cp. [1]).
VDB leaf nodes are implicit in Open VKL: they are stored as pointers to user-provided data.
[Structure of "vdb" volumes in the default
configuration][imgVdbStructure]
VDB volumes interpret input data as constant cells (which are then
potentially filtered). This is in contrast to structuredRegular
volumes, which have a vertex-centered interpretation.
The VDB implementation in Open VKL follows the following goals:
-
Efficient data structure traversal on vector architectures.
-
Enable the use of industry-standard .vdb files created through the OpenVDB library.
-
Compatibility with OpenVDB on a leaf data level, so that .vdb files may be loaded with minimal overhead.
VDB volumes have the following parameters:
| Type | Name | Default | Description |
|---|---|---|---|
| int | type | The field type. Only VKL_FLOAT is supported at the moment. Use the enum VKLDataType for named constants. |
|
| int | filter | VKL_FILTER_TRILINEAR |
The filter used for reconstructing the field. Use VKLFilter for named constants. |
| int | maxSamplingDepth | VKL_VDB_NUM_LEVELS |
Do not descend further than to this depth during sampling. |
| int | maxIteratorDepth | 3 | Do not descend further than to this depth during interval iteration. The maximum value is 3. |
| float[] | indexToObject | 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0 | An array of 12 values of type float that define the transformation from index space to object space. In index space, the grid is an axis-aligned regular grid, and leaf voxels have size (1,1,1). The first 9 values are interpreted as a row-major linear transformation matrix. The last 3 values are the translation of the grid origin. |
| uint32[] | level | For each input node, the level on which this node exists. Levels are counted from the root level (0) down. Input nodes may be on levels [1, VKL_VDB_NUM_LEVELS-1]. |
|
| vec3i[] | origin | For each input node, the node origin index. | |
| uint32[] | format | For each input node, the data format. Currently supported are VKL_VDB_FORMAT_TILE for tiles, and VKL_VDB_FORMAT_CONSTANT for nodes that are dense regular grids, but temporally constant. |
|
| VKLData[] | data | Node data. Nodes with format VKL_VDB_FORMAT_TILE are expected to have single-entry arrays. Nodes with format VKL_VDB_FORMAT_CONSTANT are expected to have arrays with vklVdbLevelNumVoxels(level[i]) entries. |
Configuration parameters for VDB ("vdb") volumes.
The level, origin, format, and data parameters must have the same size,
and there must be at least one valid node or commit() will fail.
VDB volumes support the following observers:
| Name | Buffer Type | Description |
|---|---|---|
| LeafNodeAccess | uint32[] | This observer returns an array with as many entries as input nodes were passed. If the input node i was accessed during traversal, then the ith entry in this array has a nonzero value. This can be used for on-demand loading of leaf nodes. |
Observers supported by VDB ("vdb") volumes.
-
Open VKL implements sampling in ISPC, and can exploit wide SIMD architectures.
-
VDB volumes in Open VKL are read-only once committed, and designed for rendering only. Authoring or manipulating datasets is not in the scope of this implementation.
-
The only supported field type is
VKL_FLOATat this point. Other field types may be supported in the future. -
The root level in Open VKL has a single node with resolution 64^3 (cp. [1]. OpenVDB uses a hash map, instead).
-
The tree topology can be configured at compile time, but this happens through the CMake option
VKL_VDB_LOG_RESOLUTION. By default this is set to “6;5;4;3”, which means that there are four levels, the root node has a resolution of (263 = 64^3), first level nodes a resolution of (253 = 32^3), and so on.
Files generated with OpenVDB can be loaded easily since Open VKL vdb
volumes implement the same leaf data layout. This means that OpenVDB
leaf data pointers can be passed to Open VKL using shared data buffers,
avoiding copy operations.
An example of this can be found in
vdb_util/include/openvkl/OpenVdbGrid.h, where the class
OpenVdbFloatGrid encapsulates the necessary operations. This class is
also accessible through the vklExamples application using the -file
and -field command line arguments.
To use this example feature, compile Open VKL with OpenVDB_ROOT
pointing to the OpenVDB prefix.
- Museth, K. VDB: High-Resolution Sparse Volumes with Dynamic Topology. ACM Transactions on Graphics 32(3), 2013. DOI: 10.1145/2487228.2487235
Computing the value of a volume at an object space coordinate is done using the sampling API. NaN is returned for probe points outside the volume.
The scalar API just takes a volume and coordinate, and returns a float value.
float vklComputeSample(VKLVolume volume, const vkl_vec3f *objectCoordinates);Vector versions allow sampling at 4, 8, or 16 positions at once.
Depending on the machine type and Open VKL driver implementation, these
can give greater performance. An active lane mask valid is passed in
as an array of integers; set 0 for lanes to be ignored, -1 for active
lanes.
void vklComputeSample4(const int *valid,
VKLVolume volume,
const vkl_vvec3f4 *objectCoordinates,
float *samples);
void vklComputeSample8(const int *valid,
VKLVolume volume,
const vkl_vvec3f8 *objectCoordinates,
float *samples);
void vklComputeSample16(const int *valid,
VKLVolume volume,
const vkl_vvec3f16 *objectCoordinates,
float *samples);All of the above sampling APIs can be used, regardless of the driver’s native SIMD width.
In a very similar API to vklComputeSample, vklComputeGradient
queries the value gradient at an object space coordinate. Again, a
scalar API, now returning a vec3f instead of a float. NaN values are
returned for points outside the volume.
vkl_vec3f vklComputeGradient(VKLVolume volume,
const vkl_vec3f *objectCoordinates);Vector versions are also provided:
void vklComputeGradient4(const int *valid,
VKLVolume volume,
const vkl_vvec3f4 *objectCoordinates,
vkl_vvec3f4 *gradients);
void vklComputeGradient8(const int *valid,
VKLVolume volume,
const vkl_vvec3f8 *objectCoordinates,
vkl_vvec3f8 *gradients);
void vklComputeGradient16(const int *valid,
VKLVolume volume,
const vkl_vvec3f16 *objectCoordinates,
vkl_vvec3f16 *gradients);All of the above gradient APIs can be used, regardless of the driver’s native SIMD width.
Open VKL has APIs to search for particular volume values along a ray.
Queries can be for ranges of volume values (vklIterateInterval) or for
particular values (vklIterateHit). The desired values are set in a
VKLValueSelector, which needs to be created, filled in with values,
and then committed.
VKLValueSelector vklNewValueSelector(VKLVolume volume);
void vklValueSelectorSetRanges(VKLValueSelector valueSelector,
size_t numRanges,
const vkl_range1f *ranges);
void vklValueSelectorSetValues(VKLValueSelector valueSelector,
size_t numValues,
const float *values);To query an interval, a VKLIntervalIterator of scalar or vector width
must be initialized with vklInitIntervalIterator. The iterator
structure is allocated and belongs to the caller, and initialized by the
following functions.
void vklInitIntervalIterator(VKLIntervalIterator *iterator,
VKLVolume volume,
const vkl_vec3f *origin,
const vkl_vec3f *direction,
const vkl_range1f *tRange,
VKLValueSelector valueSelector);
void vklInitIntervalIterator4(const int *valid,
VKLIntervalIterator4 *iterator,
VKLVolume volume,
const vkl_vvec3f4 *origin,
const vkl_vvec3f4 *direction,
const vkl_vrange1f4 *tRange,
VKLValueSelector valueSelector);
void vklInitIntervalIterator8(const int *valid,
VKLIntervalIterator8 *iterator,
VKLVolume volume,
const vkl_vvec3f8 *origin,
const vkl_vvec3f8 *direction,
const vkl_vrange1f8 *tRange,
VKLValueSelector valueSelector);
void vklInitIntervalIterator16(const int *valid,
VKLIntervalIterator16 *iterator,
VKLVolume volume,
const vkl_vvec3f16 *origin,
const vkl_vvec3f16 *direction,
const vkl_vrange1f16 *tRange,
VKLValueSelector valueSelector);Intervals can then be processed by calling vklIterateInterval as long
as the returned lane masks indicates that the iterator is still within
the volume:
int vklIterateInterval(VKLIntervalIterator *iterator,
VKLInterval *interval);
void vklIterateInterval4(const int *valid,
VKLIntervalIterator4 *iterator,
VKLInterval4 *interval,
int *result);
void vklIterateInterval8(const int *valid,
VKLIntervalIterator8 *iterator,
VKLInterval8 *interval,
int *result);
void vklIterateInterval16(const int *valid,
VKLIntervalIterator16 *iterator,
VKLInterval16 *interval,
int *result);The intervals returned have a t-value range, a value range, and a
nominalDeltaT which is approximately the step size that should be used
to walk through the interval, if desired. The number and length of
intervals returned is volume type implementation dependent. There is
currently no way of requesting a particular splitting.
typedef struct
{
vkl_range1f tRange;
vkl_range1f valueRange;
float nominalDeltaT;
} VKLInterval;
typedef struct
{
vkl_vrange1f4 tRange;
vkl_vrange1f4 valueRange;
float nominalDeltaT[4];
} VKLInterval4;
typedef struct
{
vkl_vrange1f8 tRange;
vkl_vrange1f8 valueRange;
float nominalDeltaT[8];
} VKLInterval8;
typedef struct
{
vkl_vrange1f16 tRange;
vkl_vrange1f16 valueRange;
float nominalDeltaT[16];
} VKLInterval16;Querying for particular values is done using a VKLHitIterator in much
the same fashion. This API could be used, for example, to find
isosurfaces. Again, a user allocated VKLHitIterator of the desired
width must be initialized:
void vklInitHitIterator(VKLHitIterator *iterator,
VKLVolume volume,
const vkl_vec3f *origin,
const vkl_vec3f *direction,
const vkl_range1f *tRange,
VKLValueSelector valueSelector);
void vklInitHitIterator4(const int *valid,
VKLHitIterator4 *iterator,
VKLVolume volume,
const vkl_vvec3f4 *origin,
const vkl_vvec3f4 *direction,
const vkl_vrange1f4 *tRange,
VKLValueSelector valueSelector);
void vklInitHitIterator8(const int *valid,
VKLHitIterator8 *iterator,
VKLVolume volume,
const vkl_vvec3f8 *origin,
const vkl_vvec3f8 *direction,
const vkl_vrange1f8 *tRange,
VKLValueSelector valueSelector);
void vklInitHitIterator16(const int *valid,
VKLHitIterator16 *iterator,
VKLVolume volume,
const vkl_vvec3f16 *origin,
const vkl_vvec3f16 *direction,
const vkl_vrange1f16 *tRange,
VKLValueSelector valueSelector);Hits are then queried by looping a call to vklIterateHit as long as
the returned lane mask indicates that the iterator is still within the
volume.
int vklIterateHit(VKLHitIterator *iterator, VKLHit *hit);
void vklIterateHit4(const int *valid,
VKLHitIterator4 *iterator,
VKLHit4 *hit,
int *result);
void vklIterateHit8(const int *valid,
VKLHitIterator8 *iterator,
VKLHit8 *hit,
int *result);
void vklIterateHit16(const int *valid,
VKLHitIterator16 *iterator,
VKLHit16 *hit,
int *result);Returned hits consist of the t-value and volume value at that location:
typedef struct
{
float t;
float sample;
} VKLHit;
typedef struct
{
float t[4];
float sample[4];
} VKLHit4;
typedef struct
{
float t[8];
float sample[8];
} VKLHit8;
typedef struct
{
float t[16];
float sample[16];
} VKLHit16;For both interval and hit iterators, only the vector-wide API for the
native SIMD width (determined via vklGetNativeSIMDWidth can be called.
The scalar versions are always valid. This restriction will likely be
lifted in the future.
It is strongly recommended to have the Flush to Zero and Denormals are Zero mode of the MXCSR control and status register enabled for each
thread before calling the sampling, gradient, or interval API functions.
Otherwise, under some circumstances special handling of denormalized
floating point numbers can significantly reduce application and Open VKL
performance. The driver parameter flushDenormals or environment
variable OPENVKL_FLUSH_DENORMALS can be used to toggle this mode; by
default it is enabled. Alternatively, when using Open VKL together with
the Intel® Threading Building Blocks, it is sufficient to execute the
following code at the beginning of the application main thread (before
the creation of the tbb::task_scheduler_init object):
#include <xmmintrin.h>
#include <pmmintrin.h>
...
_MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON);
_MM_SET_DENORMALS_ZERO_MODE(_MM_DENORMALS_ZERO_ON);If using a different tasking system, make sure each thread calling into Open VKL has the proper mode set.
Open VKL ships with simple tutorial applications demonstrating the basic usage of the API, as well as full renderers showing recommended usage.
Simple tutorials can be found in the examples/ directory. These are:
vklTutorial.c: usage of the C APIvklTutorialISPC.[cpp,ispc]: combined usage of the C and ISPC APIs
For quick reference, the contents of vklTutorial.c are shown below.
#include <openvkl/openvkl.h>
#include <stdio.h>
void demoScalarAPI(VKLVolume volume)
{
printf("demo of 1-wide API\n");
// bounding box
vkl_box3f bbox = vklGetBoundingBox(volume);
printf("\tbounding box\n");
printf("\t\tlower = %f %f %f\n", bbox.lower.x, bbox.lower.y, bbox.lower.z);
printf("\t\tupper = %f %f %f\n\n", bbox.upper.x, bbox.upper.y, bbox.upper.z);
// value range
vkl_range1f valueRange = vklGetValueRange(volume);
printf("\tvalue range = (%f %f)\n\n", valueRange.lower, valueRange.upper);
// sample, gradient
vkl_vec3f coord = {1.f, 1.f, 1.f};
float sample = vklComputeSample(volume, &coord);
vkl_vec3f grad = vklComputeGradient(volume, &coord);
printf("\tcoord = %f %f %f\n", coord.x, coord.y, coord.z);
printf("\t\tsample = %f\n", sample);
printf("\t\tgrad = %f %f %f\n\n", grad.x, grad.y, grad.z);
// value selector setup (note the commit at the end)
vkl_range1f ranges[2] = {{10, 20}, {50, 75}};
int num_ranges = 2;
float values[2] = {32, 96};
int num_values = 2;
VKLValueSelector selector = vklNewValueSelector(volume);
vklValueSelectorSetRanges(selector, num_ranges, ranges);
vklValueSelectorSetValues(selector, num_values, values);
vklCommit(selector);
// ray definition for iterators
vkl_vec3f rayOrigin = {0, 0, 0};
vkl_vec3f rayDirection = {1, 0, 0};
vkl_range1f rayTRange = {0, 200};
printf("\trayOrigin = %f %f %f\n", rayOrigin.x, rayOrigin.y, rayOrigin.z);
printf("\trayDirection = %f %f %f\n",
rayDirection.x,
rayDirection.y,
rayDirection.z);
printf("\trayTRange = %f %f\n", rayTRange.lower, rayTRange.upper);
// interval iteration
VKLIntervalIterator intervalIterator;
vklInitIntervalIterator(&intervalIterator,
volume,
&rayOrigin,
&rayDirection,
&rayTRange,
selector);
printf("\n\tinterval iterator for value ranges {%f %f} {%f %f}\n",
ranges[0].lower,
ranges[0].upper,
ranges[1].lower,
ranges[1].upper);
for (;;) {
VKLInterval interval;
int result = vklIterateInterval(&intervalIterator, &interval);
if (!result)
break;
printf(
"\t\ttRange (%f %f)\n\t\tvalueRange (%f %f)\n\t\tnominalDeltaT %f\n\n",
interval.tRange.lower,
interval.tRange.upper,
interval.valueRange.lower,
interval.valueRange.upper,
interval.nominalDeltaT);
}
// hit iteration
VKLHitIterator hitIterator;
vklInitHitIterator(
&hitIterator, volume, &rayOrigin, &rayDirection, &rayTRange, selector);
printf("\thit iterator for values %f %f\n", values[0], values[1]);
for (;;) {
VKLHit hit;
int result = vklIterateHit(&hitIterator, &hit);
if (!result)
break;
printf("\t\tt %f\n\t\tsample %f\n\n", hit.t, hit.sample);
}
vklRelease(selector);
}
void demoVectorAPI(VKLVolume volume)
{
printf("demo of 4-wide API (8- and 16- follow the same pattern)\n");
vkl_vvec3f4 coord4; // structure-of-array layout
int valid[4];
for (int i = 0; i < 4; i++) {
coord4.x[i] = coord4.y[i] = coord4.z[i] = i;
valid[i] = -1; // valid mask: 0 = not valid, -1 = valid
}
float sample4[4];
vkl_vvec3f4 grad4;
vklComputeSample4(valid, volume, &coord4, sample4);
vklComputeGradient4(valid, volume, &coord4, &grad4);
for (int i = 0; i < 4; i++) {
printf("\tcoord[%d] = %f %f %f\n", i, coord4.x[i], coord4.y[i], coord4.z[i]);
printf("\t\tsample[%d] = %f\n", i, sample4[i]);
printf("\t\tgrad[%d] = %f %f %f\n", i, grad4.x[i], grad4.y[i], grad4.z[i]);
}
}
int main()
{
vklLoadModule("ispc_driver");
VKLDriver driver = vklNewDriver("ispc");
vklCommitDriver(driver);
vklSetCurrentDriver(driver);
int dimensions[] = {128, 128, 128};
const int numVoxels = dimensions[0] * dimensions[1] * dimensions[2];
VKLVolume volume = vklNewVolume("structuredRegular");
vklSetVec3i(volume, "dimensions", dimensions[0], dimensions[1], dimensions[2]);
vklSetVec3f(volume, "gridOrigin", 0, 0, 0);
vklSetVec3f(volume, "gridSpacing", 1, 1, 1);
float *voxels = malloc(numVoxels * sizeof(float));
if (!voxels) {
printf("failed to allocate voxel memory!\n");
return 1;
}
// x-grad sample volume
for (int k = 0; k < dimensions[2]; k++)
for (int j = 0; j < dimensions[1]; j++)
for (int i = 0; i < dimensions[0]; i++)
voxels[k * dimensions[0] * dimensions[1] + j * dimensions[2] + i] =
(float)i;
VKLData data = vklNewData(numVoxels, VKL_FLOAT, voxels, 0);
vklSetData(volume, "data", data);
vklRelease(data);
vklCommit(volume);
demoScalarAPI(volume);
demoVectorAPI(volume);
vklRelease(volume);
vklShutdown();
free(voxels);
return 0;
}Open VKL also ships with an interactive example application,
vklExamples. This interactive viewer demonstrates multiple example
renderers including a path tracer, isosurface renderer (using hit
iterators), and ray marcher. The viewer UI supports switching between
renderers interactively.
Each renderer has both a C++ and ISPC implementation showing recommended
API usage. These implementations are available in the
examples/interactive/renderers/ directory.
The latest Open VKL sources are always available at the Open VKL GitHub
repository. The default master
branch should always point to the latest tested bugfix release.
Open VKL currently supports Linux, Mac OS X, and Windows. In addition, before you can build Open VKL you need the following prerequisites:
-
You can clone the latest Open VKL sources via:
git clone https://github.com/openvkl/openvkl.git -
To build Open VKL you need CMake, any form of C++11 compiler (we recommend using GCC, but also support Clang and MSVC), and standard Linux development tools. To build the examples, you should also have some version of OpenGL.
-
Additionally you require a copy of the Intel® SPMD Program Compiler (ISPC), version 1.12.0 or later. Please obtain a release of ISPC from the ISPC downloads page.
-
Open VKL depends on the OSPRay common library, ospcommon. ospcommon is available at the ospcommon GitHub repository.
-
Open VKL depends on Embree, which is available at the Embree GitHub repository.
Depending on your Linux distribution you can install these dependencies
using yum or apt-get. Some of these packages might already be
installed or might have slightly different names.
For convenience, Open VKL provides a CMake Superbuild script which will pull down Open VKL’s dependencies and build Open VKL itself. The result is an install directory, with each dependency in its own directory.
Run with:
mkdir build
cd build
cmake [<VKL_ROOT>/superbuild]
cmake --build .The resulting install directory (or the one set with
CMAKE_INSTALL_PREFIX) will have everything in it, with one
subdirectory per dependency.
CMake options to note (all have sensible defaults):
CMAKE_INSTALL_PREFIXwill be the root directory where everything gets installed.BUILD_JOBSsets the number given tomake -jfor parallel builds.INSTALL_IN_SEPARATE_DIRECTORIEStoggles installation of all libraries in separate or the same directory.
For the full set of options, run ccmake [<VKL_ROOT>/superbuild].
Assuming the above prerequisites are all fulfilled, building Open VKL through CMake is easy:
-
Create a build directory, and go into it
mkdir openvkl/build cd openvkl/build(We do recommend having separate build directories for different configurations such as release, debug, etc.).
-
The compiler CMake will use will default to whatever the
CCandCXXenvironment variables point to. Should you want to specify a different compiler, run cmake manually while specifying the desired compiler. The default compiler on most linux machines isgcc, but it can be pointed toclanginstead by executing the following:cmake -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_C_COMPILER=clang ..CMake will now use Clang instead of GCC. If you are ok with using the default compiler on your system, then simply skip this step. Note that the compiler variables cannot be changed after the first
cmakeorccmakerun. -
Open the CMake configuration dialog
ccmake .. -
Make sure to properly set build mode and enable the components you need, etc.; then type ’c’onfigure and ’g’enerate. When back on the command prompt, build it using
make -
You should now have
libopenvkl.soas well as the tutorial / example applications.
This page gives a brief (and incomplete) list of other projects that make use of Open VKL, as well as a set of related links to other projects and related information.
If you have a project that makes use of Open VKL and would like this to be listed here, please let us know.
- Intel® OSPRay, a ray tracing based rendering engine for high-fidelity visualization
-
The Intel® Embree Ray Tracing Kernel Framework
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