SoVolumeTransform Class Reference
[Nodes]

Transform data before texture creation. More...

#include <VolumeViz/nodes/SoVolumeTransform.h>

Inheritance diagram for SoVolumeTransform:

Classes
struct	MTstruct
	thread specific variables
Public Member Functions
virtual SoType	getTypeId () const
	SoVolumeTransform ()
virtual void	apply (SoState state, const SoLDM::DataSetIdPair &p, SoBufferObject bufferObject, const SoLDMTileID &id)=0
virtual SbBool	isValid (SoState state, const SoLDM::DataSetIdPair &p, SoBufferObject bufferObject, const SoLDMTileID &id)
virtual void	getTransformedMinMax (double &min, double &max)
SoBufferObject *	getFromCache (const SoLDMTileID &tileID)
void	addInCache (const SoLDMTileID &tileID, SoBufferObject *bufferObject)
Static Public Member Functions
static SoType	getClassTypeId ()
Public Attributes
SoSFShort	volumeTransformId
SoSFInt32	cacheSize

Detailed Description

Transform data before texture creation.

The SoVolumeTransform node allows an application to apply a defined computation on LDM data tiles just before they are sent to the GPU. There are several other ways to apply a computation to LDM tiles, that are applied at different stages of the pipeline. The SoLDMDataTransform class for example (see the dataTransform field of SoDataSet) applies a computation to each LDM tile requested from the volume reader before the tile is stored in system memory. This can be used to create multiple data sets from a single input (e.g. on disk) data set, but has the drawback that each resulting data set must be stored in system memory. SoVolumeTransform can be used to create multiple data sets from a single data set in system memory and does not require storing the created data sets in system memory (only on the GPU).

A cache mechanism, local to each instance of SoVolumeTransform, allows storing the computed tiles for later reuse. The size of this cache (number of tiles to cache) can be specified using the cacheSize field. We recommend setting the cacheSize to the number of tiles needed to display the biggest expected slice. As an example, for a dataset of size 128x512x1024 with a tile size equal to 128, the biggest slice size is 512x1024. So 4x8 = 32 LDM tiles are needed for rendering and therefore a cacheSize of 32 (tiles) is needed to avoid computing the same tile multiple times. The apply method can retrieve the transformed data for other tiles from the cache and can explicitly add the transformed data for other tiles to the cache.

SoVolumeTransform works on tiles (not slices or volumes). If a compute function needs data from other tiles, the application may use the SoLDMDataAccess API to get that data. (This is another difference from SoLDMDataTransform, which does not allow using the LDM data access API.)

Multiple SoVolumeTransform nodes may be applied to the same SoDataSet. The transforms are applied in the order of their appearance in the scene graph. SoVolumeTransform nodes may also be applied only to a specific SoDataSet using the volumeTransformId field. If this field is zero (the default), the transform is applied to all subsequent data set nodes. Else the transform is only applied to data sets whose dataSetId field contains the same value as the volumeTransformId.

SoVolumeTransform is based on the Open Inventor computing framework and uses the SoBufferObject classes to abstract and manage blocks of memory. The application can use different devices to implement the computation, and manage input tiles and output tiles stored on different devices.

As mentioned previously, SoVolumeTransform can be used to create multiple data sets on-the-fly from a single data set in system memory. In this case the same data set node will be instanced multiple times in the scene graph (although its data will only be loaded in system memory once), but we still need to assign each data texture a unique id so the shader program can access them uniquely. This is done using SoDataSetId nodes to specify a different data set id for each instance of the data set node. If an SoDataSetId node is in the traversal state when a data set node is traversed, the dataSetId field is ignored and the id from the SoDataSetId node is used.

To implement a computation, the application must derive a new class from SoVolumeTransform and (at least) implement the apply() method, which performs the actual computation. This method is called with parameters that give access to information about the data set and the specific tile being computed. In a simple case you might only need to access the buffer object.

It may also be useful to implement the isValid() and getTransformedMinMax() methods. The isValid() method will be called for each tile immediately before the apply() method. If this method returns FALSE, then the apply() method will not be called for that tile. If the application can compute or estimate the min and max values of the computed data set, then it should implement the getTransformedMinMax() method so VolumeViz does not do unnecessary work to compute these values.

FILE FORMAT/DEFAULT

volumeTransformId	0
cacheSize	1

ACTION BEHAVIOR

SoCallbackAction

SoGLRenderAction

Constructor & Destructor Documentation

SoVolumeTransform::SoVolumeTransform ( )

Constructor.

Member Function Documentation

void SoVolumeTransform::addInCache	(	const SoLDMTileID &	tileID,
		SoBufferObject *	bufferObject
	)

Add the transformed data for a specific tile to the cache.

It is not necessary to call this method for the current tile, it will be added to the cache automatically. This method is useful if the apply method computes transformed data for other tiles. These tiles can be saved in the cache to avoid recomputing them later.

virtual void SoVolumeTransform::apply	(	SoState *	state,
		const SoLDM::DataSetIdPair &	p,
		SoBufferObject *	bufferObject,
		const SoLDMTileID &	id
	)			`[pure virtual]`

Apply in-place transformation to the specified dataset tile.

The application must implement this method in the derived class.

Parameters:

	state	Current traversal state.
	p	Dataset/id pair (p.first is an SoDataSet*, p.second is a dataSetId) Using the SoDataSet object you can obtain, for example, the actual data type of the data:

            SoDataSet *pDataSet = p.first;
            SoDataSet::dataType type = pDataSet->getDataType();

Parameters:

	bufferObject	The buffer that contains the data
	id	Tile to be transformed Using this id and the SoDataSet object you can obtain, for example, the actual position of the tile in the volume:

             SbBox3i32 tilePos = 
               pDataSet->getNodeFrontManager()->getTilePos( id );

static SoType SoVolumeTransform::getClassTypeId ( ) [static]

Returns the type identifier for this class.

Reimplemented from SoNode.

SoBufferObject* SoVolumeTransform::getFromCache ( const SoLDMTileID & tileID )

Returns the previously transformed data for a specific tile.

This method is useful if the apply method depends on transformed data for other tiles, for example adjacent tiles. If the needed tiles have already been transformed and saved in the cache, then it is not necessary to recompute them. Returns NULL if the tile was not found in the cache. See also the cacheSize field.

void SoVolumeTransform::getTransformedMinMax	(	double &	min,
		double &	max
	)			`[inline, virtual]`

Based on min max of the input data, this function should return the expected data range of the result (transformed) data.

virtual SoType SoVolumeTransform::getTypeId ( ) const [virtual]

Returns the type identifier for this specific instance.

Reimplemented from SoNode.

virtual SbBool SoVolumeTransform::isValid	(	SoState *	state,
		const SoLDM::DataSetIdPair &	p,
		SoBufferObject *	bufferObject,
		const SoLDMTileID &	id
	)			`[virtual]`

Should return TRUE if the given parameters are valid for this compute function.

If not the apply function will not be called for this tile. The interpretation of "valid" is up to the application. For example, you could use this function to skip computing for low resolution tiles.

Parameters:

	state	Current traversal state.
	p	Dataset/id pair (p.first is an SoDataSet*, p.second is a dataSetId)
	bufferObject	The buffer that contains the data
	id	Tile to be transformed

Member Data Documentation

SoSFInt32 SoVolumeTransform::cacheSize

Size of the computed tile cache for this transform.

This is the number of computed tiles that will be cached and will not need to be recomputed. Choose a value to balance between memory usage and computing time. Default is 1.

SoSFShort SoVolumeTransform::volumeTransformId

Allows the transform to be applied to all or one specific data set.

A volume transform id of 0 means that this transform will be applied to all subsequent data sets. A value greater than 0 means that this transform will only be applied to data sets with a matching data set id. For example, if the transform id is 1, the transform will only be applied to data sets whose data set id is also 1. The default value is 0.

The documentation for this class was generated from the following file:

VolumeViz/nodes/SoVolumeTransform.h

SoVolumeTransform Class Reference [Nodes]

Classes

Public Member Functions

Static Public Member Functions

Public Attributes

Detailed Description

FILE FORMAT/DEFAULT

ACTION BEHAVIOR

SEE ALSO

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation

SoVolumeTransform Class Reference
[Nodes]