vtkOpenGLHAVSVolumeMapper Class Reference

#include <vtkOpenGLHAVSVolumeMapper.h>

Inheritance diagram for vtkOpenGLHAVSVolumeMapper:

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Collaboration diagram for vtkOpenGLHAVSVolumeMapper:

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List of all members.

Detailed Description

Hardware-Assisted Visibility Sorting unstructured grid mapper, OpenGL implementation.

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.

Definition at line 127 of file vtkOpenGLHAVSVolumeMapper.h.


Public Types
typedef vtkHAVSVolumeMapper	Superclass
Public Member Functions
virtual const char *	GetClassName ()
virtual int	IsA (const char *type)
virtual void	PrintSelf (ostream &os, vtkIndent indent)
virtual void	Render (vtkRenderer ren, vtkVolume vol)
virtual void	ReleaseGraphicsResources (vtkWindow *)
virtual void	SetGPUDataStructures (bool)

virtual bool	SupportedByHardware (vtkRenderer *r)
Static Public Member Functions
static vtkOpenGLHAVSVolumeMapper *	New ()
static int	IsTypeOf (const char *type)
static vtkOpenGLHAVSVolumeMapper *	SafeDownCast (vtkObject *o)
Protected Member Functions
	vtkOpenGLHAVSVolumeMapper ()
	~vtkOpenGLHAVSVolumeMapper ()
virtual int	FillInputPortInformation (int port, vtkInformation *info)
virtual void	Initialize (vtkRenderer ren, vtkVolume vol)
virtual void	InitializeLookupTables (vtkVolume *vol)
void	InitializeGPUDataStructures ()
void	InitializeShaders ()
void	DeleteShaders ()
void	InitializeFramebufferObject ()
void	RenderHAVS (vtkRenderer *ren)
void	SetupFBOZBuffer (int screenWidth, int screenHeight, float depthNear, float depthFar, float *zbuffer)
void	SetupFBOMRT ()
void	DrawFBOInit (int screenWidth, int screenHeight, float depthNear, float depthFar)
void	DrawFBOGeometry ()
void	DrawFBOFlush (int screenWidth, int screenHeight, float depthNear, float depthFar)
void	DrawBlend (int screenWidth, int screenHeight, float depthNear, float depthFar)
void	CheckOpenGLError (const char *str)
Protected Attributes
unsigned int	VBOVertexName
unsigned int	VBOTexCoordName
unsigned int	VBOVertexIndexName
unsigned int	VertexProgram
unsigned int	FragmentProgramBegin
unsigned int	FragmentProgram
unsigned int	FragmentProgramEnd
unsigned int	FramebufferObject
int	FramebufferObjectSize
unsigned int	FramebufferTextures [4]
unsigned int	DepthTexture
unsigned int	PsiTableTexture
unsigned int	TransferFunctionTexture
vtkWeakPointer< vtkRenderWindow >	RenderWindow

Member Typedef Documentation

typedef vtkHAVSVolumeMapper vtkOpenGLHAVSVolumeMapper::Superclass

Reimplemented from vtkHAVSVolumeMapper.

Definition at line 132 of file vtkOpenGLHAVSVolumeMapper.h.

Constructor & Destructor Documentation

vtkOpenGLHAVSVolumeMapper::vtkOpenGLHAVSVolumeMapper ( ) [protected]

vtkOpenGLHAVSVolumeMapper::~vtkOpenGLHAVSVolumeMapper ( ) [protected]

Member Function Documentation

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

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

Reimplemented from vtkHAVSVolumeMapper.

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

Reimplemented from vtkHAVSVolumeMapper.

static int vtkOpenGLHAVSVolumeMapper::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 vtkHAVSVolumeMapper.

virtual int vtkOpenGLHAVSVolumeMapper::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 vtkHAVSVolumeMapper.

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

Reimplemented from vtkHAVSVolumeMapper.

virtual void vtkOpenGLHAVSVolumeMapper::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 vtkHAVSVolumeMapper.

virtual void vtkOpenGLHAVSVolumeMapper::Render	(	vtkRenderer *	ren,
		vtkVolume *	vol
	)			`[virtual]`

Render the volume

Implements vtkUnstructuredGridVolumeMapper.

virtual void vtkOpenGLHAVSVolumeMapper::ReleaseGraphicsResources ( vtkWindow * ) [virtual]

Release any graphics resources that are being consumed by this volume renderer.

Reimplemented from vtkUnstructuredGridVolumeMapper.

virtual void vtkOpenGLHAVSVolumeMapper::SetGPUDataStructures ( bool ) [virtual]

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

Implements vtkHAVSVolumeMapper.

virtual bool vtkOpenGLHAVSVolumeMapper::SupportedByHardware ( vtkRenderer * r ) [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.

virtual int vtkOpenGLHAVSVolumeMapper::FillInputPortInformation	(	int	port,
		vtkInformation *	info
	)			`[protected, virtual]`

Fill the input port information objects for this algorithm. This is invoked by the first call to GetInputPortInformation for each port so subclasses can specify what they can handle.

Reimplemented from vtkUnstructuredGridVolumeMapper.