vtkHAVSVolumeMapper Class Reference

#include <vtkHAVSVolumeMapper.h>

Inheritance diagram for vtkHAVSVolumeMapper:

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Collaboration diagram for vtkHAVSVolumeMapper:

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List of all members.

Detailed Description

Hardware-Assisted Visibility Sorting unstructured grid mapper.

vtkHAVSVolumeMapper is a class that renders polygonal data (represented as an unstructured grid) using the Hardware-Assisted Visibility Sorting (HAVS) algorithm. First the unique triangles are sorted in object space, then they are sorted in image space using a fixed size A-buffer implemented on the GPU called the k-buffer. The HAVS algorithm excels at rendering large datasets quickly. The trade-off is that the algorithm may produce some rendering artifacts due to an insufficient k size (currently 2 or 6 is supported) or read/write race conditions.

A built in level-of-detail (LOD) approach samples the geometry using one of two heuristics (field or area). If LOD is enabled, the amount of geometry that is sampled and rendered changes dynamically to stay within the target frame rate. The field sampling method generally works best for datasets with cell sizes that don't vary much in size. On the contrary, the area sampling approach gives better approximations when the volume has a lot of variation in cell size.

The HAVS algorithm uses several advanced features on graphics hardware. The k-buffer sorting network is implemented using framebuffer objects (FBOs) with multiple render targets (MRTs). Therefore, only cards that support these features can run the algorithm (at least an ATI 9500 or an NVidia NV40 (6600)).

Attention:

Several issues had to be addressed to get the HAVS algorithm working within the vtk framework. These additions forced the code to forsake speed for the sake of compliance and robustness.

The HAVS algorithm operates on the triangles that compose the mesh. Therefore, before rendering, the cells are decomposed into unique triangles and stored on the GPU for efficient rendering. The use of GPU data structures is only recommended if the entire geometry can fit in graphics memory. Otherwise this feature should be disabled.

Another new feature is the handling of mixed data types (eg., polygonal data with volume data). This is handled by reading the z-buffer from the current window and copying it into the framebuffer object for off-screen rendering. The depth test is then enabled so that the volume only appears over the opaque geometry. Finally, the results of the off-screen rendering are blended into the framebuffer as a transparent, view-aligned texture.

Instead of using a preintegrated 3D lookup table for storing the ray integral, this implementation uses partial pre-integration. This improves the performance of dynamic transfer function updates by avoiding a costly preprocess of the table.

A final change to the original algorithm is the handling of non-convexities in the mesh. Due to read/write hazards that may create undesired artifacts with non-convexities when using a inside/outside toggle in the fragment program, another approach was employed. To handle non-convexities, the fragment shader determines if a ray-gap is larger than the max cell size and kill the fragment if so. This approximation performs rather well in practice but may miss small non-convexities.

For more information on the HAVS algorithm see:

"Hardware-Assisted Visibility Sorting for Unstructured Volume Rendering" by S. P. Callahan, M. Ikits, J. L. D. Comba, and C. T. Silva, IEEE Transactions of Visualization and Computer Graphics; May/June 2005.

For more information on the Level-of-Detail algorithm, see:

"Interactive Rendering of Large Unstructured Grids Using Dynamic Level-of-Detail" by S. P. Callahan, J. L. D. Comba, P. Shirley, and C. T. Silva, Proceedings of IEEE Visualization '05, Oct. 2005.

Acknowledgments:: This code was developed by Steven P. Callahan under the supervision of Prof. Claudio T. Silva. The code also contains contributions from Milan Ikits, Linh Ha, Huy T. Vo, Carlos E. Scheidegger, and Joao L. D. Comba.

Acknowledgments:: The work was supported by grants, contracts, and gifts from the National Science Foundation, the Department of Energy, the Army Research Office, and IBM.

Acknowledgments:: The port of HAVS to VTK and ParaView has been primarily supported by Sandia National Labs.

Tests:: vtkHAVSVolumeMapper (Tests)

Definition at line 134 of file vtkHAVSVolumeMapper.h.


Public Types
typedef vtkUnstructuredGridVolumeMapper	Superclass
Public Member Functions
virtual const char *	GetClassName ()
virtual int	IsA (const char *type)
virtual void	PrintSelf (ostream &os, vtkIndent indent)

virtual void	SetPartiallyRemoveNonConvexities (bool)
virtual bool	GetPartiallyRemoveNonConvexities ()

virtual void	SetLevelOfDetailTargetTime (float)
virtual float	GetLevelOfDetailTargetTime ()

virtual void	SetLevelOfDetail (bool)
virtual bool	GetLevelOfDetail ()

void	SetLevelOfDetailMethod (int)
virtual int	GetLevelOfDetailMethod ()
void	SetLevelOfDetailMethodField ()
void	SetLevelOfDetailMethodArea ()

virtual void	SetKBufferSize (int)
virtual int	GetKBufferSize ()
void	SetKBufferSizeTo2 ()
void	SetKBufferSizeTo6 ()

virtual bool	SupportedByHardware (vtkRenderer *vtkNotUsed(r))

virtual void	SetGPUDataStructures (bool)=0
virtual bool	GetGPUDataStructures ()
Static Public Member Functions
static vtkHAVSVolumeMapper *	New ()
static int	IsTypeOf (const char *type)
static vtkHAVSVolumeMapper *	SafeDownCast (vtkObject *o)
Protected Types
enum	{ NO_INIT_ERROR = 0, NON_TETRAHEDRA = 1, UNSUPPORTED_EXTENSIONS = 2, NO_SCALARS = 3, CELL_DATA = 4, NO_CELLS = 5 }
Protected Member Functions
	vtkHAVSVolumeMapper ()
	~vtkHAVSVolumeMapper ()
virtual void	Initialize (vtkRenderer ren, vtkVolume vol)=0
void	InitializePrimitives (vtkVolume *vol)
void	InitializeScalars ()
void	InitializeLevelOfDetail ()
void	InitializeLookupTables (vtkVolume *vol)
void	FRadixSort (vtkHAVSSortedFace array, vtkHAVSSortedFace temp, int lo, int up)
void	FRadix (int byte, int len, vtkHAVSSortedFace source, vtkHAVSSortedFace dest, int *count)
void	UpdateLevelOfDetail (float targetTime)
void	PartialVisibilitySort (float *eye)
bool	CheckInitializationError ()
Protected Attributes
float *	Vertices
float *	Scalars
double	ScalarRange [2]
unsigned int *	Triangles
unsigned int *	OrderedTriangles
vtkHAVSSortedFace *	SortedFaces
vtkHAVSSortedFace *	RadixTemp
float *	Centers
unsigned int	NumberOfVertices
unsigned int	NumberOfCells
unsigned int	NumberOfScalars
unsigned int	NumberOfTriangles
unsigned int	NumberOfBoundaryTriangles
unsigned int	NumberOfInternalTriangles
unsigned int *	BoundaryTriangles
unsigned int *	InternalTriangles
unsigned int	LevelOfDetailTriangleCount
float	CurrentLevelOfDetail
float	LevelOfDetailTargetTime
bool	LevelOfDetail
int	LevelOfDetailMethod
int	KBufferState
float	MaxEdgeLength
float	LevelOfDetailMaxEdgeLength
float	UnitDistance
bool	GPUDataStructures
float	Diagonal
bool	PartiallyRemoveNonConvexities
int	KBufferSize
float *	TransferFunction
int	TransferFunctionSize
bool	Initialized
int	InitializationError
int	FrameNumber
float	TotalRenderTime
vtkTimeStamp	ColorTransferFunctionMTime
vtkTimeStamp	AlphaTransferFunctionMTime
vtkTimeStamp	UnstructuredGridMTime
vtkTimeStamp	ScalarsMTime
vtkVolume *	LastVolume

Member Typedef Documentation

typedef vtkUnstructuredGridVolumeMapper vtkHAVSVolumeMapper::Superclass

Reimplemented from vtkUnstructuredGridVolumeMapper.

Reimplemented in vtkOpenGLHAVSVolumeMapper.

Definition at line 139 of file vtkHAVSVolumeMapper.h.

Member Enumeration Documentation

anonymous enum [protected]

Enumerator:

NO_INIT_ERROR
NON_TETRAHEDRA
UNSUPPORTED_EXTENSIONS
NO_SCALARS
CELL_DATA
NO_CELLS

Definition at line 215 of file vtkHAVSVolumeMapper.h.

Constructor & Destructor Documentation

vtkHAVSVolumeMapper::vtkHAVSVolumeMapper ( ) [protected]

vtkHAVSVolumeMapper::~vtkHAVSVolumeMapper ( ) [protected]

Member Function Documentation

static vtkHAVSVolumeMapper* vtkHAVSVolumeMapper::New ( ) [static]

Create an object with Debug turned off, modified time initialized to zero, and reference counting on.

Reimplemented from vtkAlgorithm.

Reimplemented in vtkOpenGLHAVSVolumeMapper.

virtual const char* vtkHAVSVolumeMapper::GetClassName ( ) [virtual]

Reimplemented from vtkUnstructuredGridVolumeMapper.

Reimplemented in vtkOpenGLHAVSVolumeMapper.

static int vtkHAVSVolumeMapper::IsTypeOf ( const char * name ) [static]

Return 1 if this class type is the same type of (or a subclass of) the named class. Returns 0 otherwise. This method works in combination with vtkTypeMacro found in vtkSetGet.h.

Reimplemented from vtkUnstructuredGridVolumeMapper.

Reimplemented in vtkOpenGLHAVSVolumeMapper.

virtual int vtkHAVSVolumeMapper::IsA ( const char * name ) [virtual]

Return 1 if this class is the same type of (or a subclass of) the named class. Returns 0 otherwise. This method works in combination with vtkTypeMacro found in vtkSetGet.h.

Reimplemented from vtkUnstructuredGridVolumeMapper.

Reimplemented in vtkOpenGLHAVSVolumeMapper.

static vtkHAVSVolumeMapper* vtkHAVSVolumeMapper::SafeDownCast ( vtkObject * o ) [static]

Reimplemented from vtkUnstructuredGridVolumeMapper.

Reimplemented in vtkOpenGLHAVSVolumeMapper.

virtual void vtkHAVSVolumeMapper::PrintSelf	(	ostream &	os,
		vtkIndent	indent
	)			`[virtual]`

Methods invoked by print to print information about the object including superclasses. Typically not called by the user (use Print() instead) but used in the hierarchical print process to combine the output of several classes.

Reimplemented from vtkUnstructuredGridVolumeMapper.

Reimplemented in vtkOpenGLHAVSVolumeMapper.

virtual void vtkHAVSVolumeMapper::SetPartiallyRemoveNonConvexities ( bool ) [virtual]

regions by removing ray segments larger than the max cell size.

virtual bool vtkHAVSVolumeMapper::GetPartiallyRemoveNonConvexities ( ) [virtual]

regions by removing ray segments larger than the max cell size.

virtual void vtkHAVSVolumeMapper::SetLevelOfDetailTargetTime ( float ) [virtual]

Set/get the desired level of detail target time measured in frames/sec.

virtual float vtkHAVSVolumeMapper::GetLevelOfDetailTargetTime ( ) [virtual]

Set/get the desired level of detail target time measured in frames/sec.

virtual void vtkHAVSVolumeMapper::SetLevelOfDetail ( bool ) [virtual]

Turn on/off level-of-detail volume rendering

virtual bool vtkHAVSVolumeMapper::GetLevelOfDetail ( ) [virtual]

Turn on/off level-of-detail volume rendering

void vtkHAVSVolumeMapper::SetLevelOfDetailMethod ( int )

Set/get the current level-of-detail method

virtual int vtkHAVSVolumeMapper::GetLevelOfDetailMethod ( ) [virtual]

Set/get the current level-of-detail method

void vtkHAVSVolumeMapper::SetLevelOfDetailMethodField ( ) [inline]

Set/get the current level-of-detail method

Definition at line 165 of file vtkHAVSVolumeMapper.h.

void vtkHAVSVolumeMapper::SetLevelOfDetailMethodArea ( ) [inline]

Set/get the current level-of-detail method

Definition at line 167 of file vtkHAVSVolumeMapper.h.

virtual void vtkHAVSVolumeMapper::SetKBufferSize ( int ) [virtual]

Set the kbuffer size

virtual int vtkHAVSVolumeMapper::GetKBufferSize ( ) [virtual]

Set the kbuffer size

void vtkHAVSVolumeMapper::SetKBufferSizeTo2 ( ) [inline]

Set the kbuffer size

Definition at line 175 of file vtkHAVSVolumeMapper.h.

void vtkHAVSVolumeMapper::SetKBufferSizeTo6 ( ) [inline]

Set the kbuffer size

Definition at line 177 of file vtkHAVSVolumeMapper.h.

virtual bool vtkHAVSVolumeMapper::SupportedByHardware ( vtkRenderer * vtkNotUsedr ) [inline, virtual]

Check hardware support for the HAVS algorithm. Necessary features include off-screen rendering, 32-bit fp textures, multiple render targets, and framebuffer objects. Subclasses must override this method to indicate if supported by Hardware.

Definition at line 186 of file vtkHAVSVolumeMapper.h.

virtual void vtkHAVSVolumeMapper::SetGPUDataStructures ( bool ) [pure virtual]

Set/get whether or not the data structures should be stored on the GPU for better peformance.

Implemented in vtkOpenGLHAVSVolumeMapper.

virtual bool vtkHAVSVolumeMapper::GetGPUDataStructures ( ) [virtual]

Set/get whether or not the data structures should be stored on the GPU for better peformance.