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 vtkOpenGLHAVSVolumeMapperNew ()
static int IsTypeOf (const char *type)
static vtkOpenGLHAVSVolumeMapperSafeDownCast (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< vtkRenderWindowRenderWindow

Member Typedef Documentation

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.

virtual void vtkOpenGLHAVSVolumeMapper::Initialize ( vtkRenderer ren,
vtkVolume vol 
) [protected, virtual]

Implements vtkHAVSVolumeMapper.

virtual void vtkOpenGLHAVSVolumeMapper::InitializeLookupTables ( vtkVolume vol  )  [protected, virtual]

Reimplemented from vtkHAVSVolumeMapper.

void vtkOpenGLHAVSVolumeMapper::InitializeGPUDataStructures (  )  [protected]

void vtkOpenGLHAVSVolumeMapper::InitializeShaders (  )  [protected]

void vtkOpenGLHAVSVolumeMapper::DeleteShaders (  )  [protected]

void vtkOpenGLHAVSVolumeMapper::InitializeFramebufferObject (  )  [protected]

void vtkOpenGLHAVSVolumeMapper::RenderHAVS ( vtkRenderer ren  )  [protected]

void vtkOpenGLHAVSVolumeMapper::SetupFBOZBuffer ( int  screenWidth,
int  screenHeight,
float  depthNear,
float  depthFar,
float *  zbuffer 
) [protected]

void vtkOpenGLHAVSVolumeMapper::SetupFBOMRT (  )  [protected]

void vtkOpenGLHAVSVolumeMapper::DrawFBOInit ( int  screenWidth,
int  screenHeight,
float  depthNear,
float  depthFar 
) [protected]

void vtkOpenGLHAVSVolumeMapper::DrawFBOGeometry (  )  [protected]

void vtkOpenGLHAVSVolumeMapper::DrawFBOFlush ( int  screenWidth,
int  screenHeight,
float  depthNear,
float  depthFar 
) [protected]

void vtkOpenGLHAVSVolumeMapper::DrawBlend ( int  screenWidth,
int  screenHeight,
float  depthNear,
float  depthFar 
) [protected]

void vtkOpenGLHAVSVolumeMapper::CheckOpenGLError ( const char *  str  )  [protected]


Member Data Documentation

unsigned int vtkOpenGLHAVSVolumeMapper::VBOVertexName [protected]

Definition at line 177 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 178 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 179 of file vtkOpenGLHAVSVolumeMapper.h.

unsigned int vtkOpenGLHAVSVolumeMapper::VertexProgram [protected]

Definition at line 180 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 181 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 182 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 183 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 184 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 185 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 186 of file vtkOpenGLHAVSVolumeMapper.h.

unsigned int vtkOpenGLHAVSVolumeMapper::DepthTexture [protected]

Definition at line 187 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 190 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 191 of file vtkOpenGLHAVSVolumeMapper.h.

Definition at line 193 of file vtkOpenGLHAVSVolumeMapper.h.


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

Generated on Mon Sep 27 18:37:07 2010 for VTK by  doxygen 1.5.6