vtk9/Rendering/Volume/vtkUnstructuredGridVolumeRayCastMapper.cxx

/*=========================================================================

  Program:   Visualization Toolkit
  Module:    vtkUnstructuredGridVolumeRayCastMapper.cxx

  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
  All rights reserved.
  See Copyright.txt or http://www.kitware.com/Copyright.htm for details.

     This software is distributed WITHOUT ANY WARRANTY; without even
     the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
     PURPOSE.  See the above copyright notice for more information.

=========================================================================*/
#include "vtkUnstructuredGridVolumeRayCastMapper.h"

#include "vtkCamera.h"
#include "vtkDoubleArray.h"
#include "vtkEncodedGradientEstimator.h"
#include "vtkEncodedGradientShader.h"
#include "vtkFiniteDifferenceGradientEstimator.h"
#include "vtkIdList.h"
#include "vtkMath.h"
#include "vtkMultiThreader.h"
#include "vtkObjectFactory.h"
#include "vtkPlaneCollection.h"
#include "vtkPointData.h"
#include "vtkRayCastImageDisplayHelper.h"
#include "vtkRenderWindow.h"
#include "vtkRenderer.h"
#include "vtkTimerLog.h"
#include "vtkTransform.h"
#include "vtkUnstructuredGrid.h"
#include "vtkUnstructuredGridBunykRayCastFunction.h"
#include "vtkUnstructuredGridHomogeneousRayIntegrator.h"
#include "vtkUnstructuredGridPartialPreIntegration.h"
#include "vtkUnstructuredGridPreIntegration.h"
#include "vtkUnstructuredGridVolumeRayCastIterator.h"
#include "vtkVolumeProperty.h"

#include <cmath>

VTK_THREAD_RETURN_TYPE UnstructuredGridVolumeRayCastMapper_CastRays(void* arg);

vtkStandardNewMacro(vtkUnstructuredGridVolumeRayCastMapper);

vtkCxxSetObjectMacro(vtkUnstructuredGridVolumeRayCastMapper, RayCastFunction,
  vtkUnstructuredGridVolumeRayCastFunction);
vtkCxxSetObjectMacro(
  vtkUnstructuredGridVolumeRayCastMapper, RayIntegrator, vtkUnstructuredGridVolumeRayIntegrator);

// Construct a new vtkUnstructuredGridVolumeRayCastMapper with default values
vtkUnstructuredGridVolumeRayCastMapper::vtkUnstructuredGridVolumeRayCastMapper()
{
  this->ImageSampleDistance = 1.0;
  this->MinimumImageSampleDistance = 1.0;
  this->MaximumImageSampleDistance = 10.0;
  this->AutoAdjustSampleDistances = 1;

  this->ImageMemorySize[0] = 0;
  this->ImageMemorySize[1] = 0;

  this->Threader = vtkMultiThreader::New();
  this->NumberOfThreads = this->Threader->GetNumberOfThreads();

  this->Image = nullptr;

  this->RenderTimeTable = nullptr;
  this->RenderVolumeTable = nullptr;
  this->RenderRendererTable = nullptr;
  this->RenderTableSize = 0;
  this->RenderTableEntries = 0;

  this->ZBuffer = nullptr;
  this->ZBufferSize[0] = 0;
  this->ZBufferSize[1] = 0;
  this->ZBufferOrigin[0] = 0;
  this->ZBufferOrigin[1] = 0;

  this->IntermixIntersectingGeometry = 1;

  this->ImageDisplayHelper = vtkRayCastImageDisplayHelper::New();

  this->RayCastFunction = vtkUnstructuredGridBunykRayCastFunction::New();
  this->RayIntegrator = nullptr;
  this->RealRayIntegrator = nullptr;
}

// Destruct a vtkUnstructuredGridVolumeRayCastMapper - clean up any memory used
vtkUnstructuredGridVolumeRayCastMapper::~vtkUnstructuredGridVolumeRayCastMapper()
{
  this->Threader->Delete();

  delete[] this->Image;

  if (this->RenderTableSize)
  {
    delete[] this->RenderTimeTable;
    delete[] this->RenderVolumeTable;
    delete[] this->RenderRendererTable;
  }

  this->ImageDisplayHelper->Delete();

  this->SetRayCastFunction(nullptr);
  this->SetRayIntegrator(nullptr);
  if (this->RealRayIntegrator)
  {
    this->RealRayIntegrator->UnRegister(this);
  }
}

float vtkUnstructuredGridVolumeRayCastMapper::RetrieveRenderTime(vtkRenderer* ren, vtkVolume* vol)
{
  int i;

  for (i = 0; i < this->RenderTableEntries; i++)
  {
    if (this->RenderVolumeTable[i] == vol && this->RenderRendererTable[i] == ren)
    {
      return this->RenderTimeTable[i];
    }
  }

  return 0.0;
}

void vtkUnstructuredGridVolumeRayCastMapper::StoreRenderTime(
  vtkRenderer* ren, vtkVolume* vol, float time)
{
  int i;
  for (i = 0; i < this->RenderTableEntries; i++)
  {
    if (this->RenderVolumeTable[i] == vol && this->RenderRendererTable[i] == ren)
    {
      this->RenderTimeTable[i] = time;
      return;
    }
  }

  // Need to increase size
  if (this->RenderTableEntries >= this->RenderTableSize)
  {
    if (this->RenderTableSize == 0)
    {
      this->RenderTableSize = 10;
    }
    else
    {
      this->RenderTableSize *= 2;
    }

    float* oldTimePtr = this->RenderTimeTable;
    vtkVolume** oldVolumePtr = this->RenderVolumeTable;
    vtkRenderer** oldRendererPtr = this->RenderRendererTable;

    this->RenderTimeTable = new float[this->RenderTableSize];
    this->RenderVolumeTable = new vtkVolume*[this->RenderTableSize];
    this->RenderRendererTable = new vtkRenderer*[this->RenderTableSize];

    for (i = 0; i < this->RenderTableEntries; i++)
    {
      this->RenderTimeTable[i] = oldTimePtr[i];
      this->RenderVolumeTable[i] = oldVolumePtr[i];
      this->RenderRendererTable[i] = oldRendererPtr[i];
    }

    delete[] oldTimePtr;
    delete[] oldVolumePtr;
    delete[] oldRendererPtr;
  }

  this->RenderTimeTable[this->RenderTableEntries] = time;
  this->RenderVolumeTable[this->RenderTableEntries] = vol;
  this->RenderRendererTable[this->RenderTableEntries] = ren;

  this->RenderTableEntries++;
}

void vtkUnstructuredGridVolumeRayCastMapper::ReleaseGraphicsResources(vtkWindow*) {}

void vtkUnstructuredGridVolumeRayCastMapper::Render(vtkRenderer* ren, vtkVolume* vol)
{
  int i;

  // Check for input
  if (this->GetInput() == nullptr)
  {
    vtkErrorMacro(<< "No Input!");
    return;
  }

  int inputAlgPort;
  vtkAlgorithm* inputAlg = this->GetInputAlgorithm(0, 0, inputAlgPort);
  inputAlg->UpdateWholeExtent();

  this->Scalars = vtkUnstructuredGridVolumeRayCastMapper::GetScalars(this->GetInput(),
    this->ScalarMode, this->ArrayAccessMode, this->ArrayId, this->ArrayName, this->CellScalars);

  if (this->Scalars == nullptr)
  {
    vtkErrorMacro("Can't use the ray cast mapper without scalars!");
    return;
  }

  // Check to make sure we have an appropriate integrator.
  if (this->RayIntegrator)
  {
    if (this->RealRayIntegrator != this->RayIntegrator)
    {
      if (this->RealRayIntegrator)
      {
        this->RealRayIntegrator->UnRegister(this);
      }
      this->RealRayIntegrator = this->RayIntegrator;
      this->RealRayIntegrator->Register(this);
    }
  }
  else
  {

#define ESTABLISH_INTEGRATOR(classname)                                                            \
  if (!this->RealRayIntegrator || (!this->RealRayIntegrator->IsA(#classname)))                     \
  {                                                                                                \
    if (this->RealRayIntegrator)                                                                   \
      this->RealRayIntegrator->UnRegister(this);                                                   \
    this->RealRayIntegrator = classname::New();                                                    \
    this->RealRayIntegrator->Register(this);                                                       \
    this->RealRayIntegrator->Delete();                                                             \
  }

    if (this->CellScalars)
    {
      ESTABLISH_INTEGRATOR(vtkUnstructuredGridHomogeneousRayIntegrator);
    }
    else
    {
      if (vol->GetProperty()->GetIndependentComponents())
      {
        ESTABLISH_INTEGRATOR(vtkUnstructuredGridPreIntegration);
      }
      else
      {
        ESTABLISH_INTEGRATOR(vtkUnstructuredGridPartialPreIntegration);
      }
    }
  }

#undef ESTABLISH_INTEGRATOR

  // Start timing now. We didn't want to capture the update of the
  // input data in the times
  this->Timer->StartTimer();

  int oldImageMemorySize[2];
  oldImageMemorySize[0] = this->ImageMemorySize[0];
  oldImageMemorySize[1] = this->ImageMemorySize[1];

  // If we are automatically adjusting the size to achieve a desired frame
  // rate, then do that adjustment here. Base the new image sample distance
  // on the previous one and the previous render time. Don't let
  // the adjusted image sample distance be less than the minimum image sample
  // distance or more than the maximum image sample distance.
  float oldImageSampleDistance = this->ImageSampleDistance;
  if (this->AutoAdjustSampleDistances)
  {
    float oldTime = this->RetrieveRenderTime(ren, vol);
    float newTime = vol->GetAllocatedRenderTime();
    this->ImageSampleDistance *= sqrt(oldTime / newTime);
    this->ImageSampleDistance = (this->ImageSampleDistance > this->MaximumImageSampleDistance)
      ? (this->MaximumImageSampleDistance)
      : (this->ImageSampleDistance);
    this->ImageSampleDistance = (this->ImageSampleDistance < this->MinimumImageSampleDistance)
      ? (this->MinimumImageSampleDistance)
      : (this->ImageSampleDistance);
  }

  // The full image fills the viewport. First, compute the actual viewport
  // size, then divide by the ImageSampleDistance to find the full image
  // size in pixels
  int width, height;
  ren->GetTiledSize(&width, &height);
  this->ImageViewportSize[0] = static_cast<int>(width / this->ImageSampleDistance);
  this->ImageViewportSize[1] = static_cast<int>(height / this->ImageSampleDistance);

  this->ImageInUseSize[0] = this->ImageViewportSize[0];
  this->ImageInUseSize[1] = this->ImageViewportSize[1];
  this->ImageOrigin[0] = 0;
  this->ImageOrigin[1] = 0;

  // What is a power of 2 size big enough to fit this image?
  this->ImageMemorySize[0] = 32;
  this->ImageMemorySize[1] = 32;
  while (this->ImageMemorySize[0] < this->ImageInUseSize[0])
  {
    this->ImageMemorySize[0] *= 2;
  }
  while (this->ImageMemorySize[1] < this->ImageInUseSize[1])
  {
    this->ImageMemorySize[1] *= 2;
  }

  // If the old image size is much too big (more than twice in
  // either direction) then set the old width to 0 which will
  // cause the image to be recreated
  if (oldImageMemorySize[0] > 2 * this->ImageMemorySize[0] ||
    oldImageMemorySize[1] > 2 * this->ImageMemorySize[1])
  {
    oldImageMemorySize[0] = 0;
  }

  // If the old image is big enough (but not too big - we handled
  // that above) then we'll bump up our required size to the
  // previous one. This will keep us from thrashing.
  if (oldImageMemorySize[0] >= this->ImageMemorySize[0] &&
    oldImageMemorySize[1] >= this->ImageMemorySize[1])
  {
    this->ImageMemorySize[0] = oldImageMemorySize[0];
    this->ImageMemorySize[1] = oldImageMemorySize[1];
  }

  // Do we already have a texture big enough? If not, create a new one and
  // clear it.
  if (!this->Image || this->ImageMemorySize[0] > oldImageMemorySize[0] ||
    this->ImageMemorySize[1] > oldImageMemorySize[1])
  {
    // If there is an image there must be row bounds
    delete[] this->Image;

    this->Image = new unsigned char[(this->ImageMemorySize[0] * this->ImageMemorySize[1] * 4)];

    unsigned char* ucptr = this->Image;

    for (i = 0; i < this->ImageMemorySize[0] * this->ImageMemorySize[1]; i++)
    {
      *(ucptr++) = 0;
      *(ucptr++) = 0;
      *(ucptr++) = 0;
      *(ucptr++) = 0;
    }
  }

  // Capture the zbuffer if necessary
  if (this->IntermixIntersectingGeometry && ren->GetNumberOfPropsRendered())
  {
    int x1, x2, y1, y2;
    double* viewport = ren->GetViewport();
    const int* renWinSize = ren->GetRenderWindow()->GetSize();

    // turn this->ImageOrigin into (x1,y1) in window (not viewport!)
    // coordinates.
    x1 = static_cast<int>(viewport[0] * static_cast<float>(renWinSize[0]) +
      static_cast<float>(this->ImageOrigin[0]) * this->ImageSampleDistance);
    y1 = static_cast<int>(viewport[1] * static_cast<float>(renWinSize[1]) +
      static_cast<float>(this->ImageOrigin[1]) * this->ImageSampleDistance);

    // compute z buffer size
    this->ZBufferSize[0] =
      static_cast<int>(static_cast<float>(this->ImageInUseSize[0]) * this->ImageSampleDistance);
    this->ZBufferSize[1] =
      static_cast<int>(static_cast<float>(this->ImageInUseSize[1]) * this->ImageSampleDistance);

    // Use the size to compute (x2,y2) in window coordinates
    x2 = x1 + this->ZBufferSize[0] - 1;
    y2 = y1 + this->ZBufferSize[1] - 1;

    // This is the z buffer origin (in viewport coordinates)
    this->ZBufferOrigin[0] =
      static_cast<int>(static_cast<float>(this->ImageOrigin[0]) * this->ImageSampleDistance);
    this->ZBufferOrigin[1] =
      static_cast<int>(static_cast<float>(this->ImageOrigin[1]) * this->ImageSampleDistance);

    // Capture the z buffer
    this->ZBuffer = ren->GetRenderWindow()->GetZbufferData(x1, y1, x2, y2);
  }

  this->RayCastFunction->Initialize(ren, vol);

  this->RealRayIntegrator->Initialize(vol, this->Scalars);

  // Save the volume and mapper temporarily so that they can be accessed later
  this->CurrentVolume = vol;
  this->CurrentRenderer = ren;

  // Create iterators and buffers here to prevent race conditions.
  this->RayCastIterators = new vtkUnstructuredGridVolumeRayCastIterator*[this->NumberOfThreads];
  this->IntersectedCellsBuffer = new vtkIdList*[this->NumberOfThreads];
  this->IntersectionLengthsBuffer = new vtkDoubleArray*[this->NumberOfThreads];
  this->NearIntersectionsBuffer = new vtkDataArray*[this->NumberOfThreads];
  this->FarIntersectionsBuffer = new vtkDataArray*[this->NumberOfThreads];
  for (i = 0; i < this->NumberOfThreads; i++)
  {
    this->RayCastIterators[i] = this->RayCastFunction->NewIterator();
    this->IntersectionLengthsBuffer[i] = vtkDoubleArray::New();
    this->IntersectionLengthsBuffer[i]->Allocate(
      this->RayCastIterators[i]->GetMaxNumberOfIntersections());
    this->NearIntersectionsBuffer[i] = vtkDataArray::CreateDataArray(this->Scalars->GetDataType());
    this->NearIntersectionsBuffer[i]->Allocate(
      this->RayCastIterators[i]->GetMaxNumberOfIntersections());
    if (this->CellScalars)
    {
      this->IntersectedCellsBuffer[i] = vtkIdList::New();
      this->IntersectedCellsBuffer[i]->Allocate(
        this->RayCastIterators[i]->GetMaxNumberOfIntersections());
      this->FarIntersectionsBuffer[i] = this->NearIntersectionsBuffer[i];
    }
    else
    {
      this->IntersectedCellsBuffer[i] = nullptr;
      this->FarIntersectionsBuffer[i] = vtkDataArray::CreateDataArray(this->Scalars->GetDataType());
      this->FarIntersectionsBuffer[i]->Allocate(
        this->RayCastIterators[i]->GetMaxNumberOfIntersections());
    }
  }

  // Set the number of threads to use for ray casting,
  // then set the execution method and do it.
  this->Threader->SetNumberOfThreads(this->NumberOfThreads);
  this->Threader->SetSingleMethod(UnstructuredGridVolumeRayCastMapper_CastRays, (void*)this);
  this->Threader->SingleMethodExecute();

  // We don't need these anymore
  this->CurrentVolume = nullptr;
  this->CurrentRenderer = nullptr;
  for (i = 0; i < this->NumberOfThreads; i++)
  {
    this->RayCastIterators[i]->Delete();
    this->IntersectionLengthsBuffer[i]->Delete();
    this->NearIntersectionsBuffer[i]->Delete();
    if (this->CellScalars)
    {
      this->IntersectedCellsBuffer[i]->Delete();
    }
    else
    {
      this->FarIntersectionsBuffer[i]->Delete();
    }
  }
  delete[] this->RayCastIterators;
  delete[] this->IntersectedCellsBuffer;
  delete[] this->IntersectionLengthsBuffer;
  delete[] this->NearIntersectionsBuffer;
  delete[] this->FarIntersectionsBuffer;

  if (!ren->GetRenderWindow()->GetAbortRender())
  {
    float depth;
    if (this->IntermixIntersectingGeometry)
    {
      depth = this->GetMinimumBoundsDepth(ren, vol);
    }
    else
    {
      depth = -1;
    }

    this->ImageDisplayHelper->RenderTexture(vol, ren, this->ImageMemorySize,
      this->ImageViewportSize, this->ImageInUseSize, this->ImageOrigin, depth, this->Image);

    this->Timer->StopTimer();
    this->TimeToDraw = this->Timer->GetElapsedTime();
    this->StoreRenderTime(ren, vol, this->TimeToDraw);
  }
  else
  {
    this->ImageSampleDistance = oldImageSampleDistance;
  }

  delete[] this->ZBuffer;
  this->ZBuffer = nullptr;

  this->UpdateProgress(1.0);
}

VTK_THREAD_RETURN_TYPE UnstructuredGridVolumeRayCastMapper_CastRays(void* arg)
{
  // Get the info out of the input structure
  int threadID = ((vtkMultiThreader::ThreadInfo*)(arg))->ThreadID;
  int threadCount = ((vtkMultiThreader::ThreadInfo*)(arg))->NumberOfThreads;
  vtkUnstructuredGridVolumeRayCastMapper* me =
    (vtkUnstructuredGridVolumeRayCastMapper*)((vtkMultiThreader::ThreadInfo*)arg)->UserData;

  if (!me)
  {
    vtkGenericWarningMacro("The volume does not have a ray cast mapper!");
    return VTK_THREAD_RETURN_VALUE;
  }

  me->CastRays(threadID, threadCount);

  return VTK_THREAD_RETURN_VALUE;
}

template <class T>
inline void vtkUGVRCMLookupCopy(
  const T* src, T* dest, vtkIdType* lookup, int numcomponents, int numtuples)
{
  for (vtkIdType i = 0; i < numtuples; i++)
  {
    const T* srctuple = src + lookup[i] * numcomponents;
    for (int j = 0; j < numcomponents; j++)
    {
      *dest = *srctuple;
      dest++;
      srctuple++;
    }
  }
}

void vtkUnstructuredGridVolumeRayCastMapper::CastRays(int threadID, int threadCount)
{
  int i, j;
  unsigned char* ucptr;

  vtkRenderWindow* renWin = this->CurrentRenderer->GetRenderWindow();
  vtkUnstructuredGridVolumeRayCastIterator* iterator = this->RayCastIterators[threadID];

  vtkIdList* intersectedCells = this->IntersectedCellsBuffer[threadID];
  vtkDoubleArray* intersectionLengths = this->IntersectionLengthsBuffer[threadID];
  vtkDataArray* nearIntersections = this->NearIntersectionsBuffer[threadID];
  vtkDataArray* farIntersections = this->FarIntersectionsBuffer[threadID];

  for (j = 0; j < this->ImageInUseSize[1]; j++)
  {
    if (j % threadCount != threadID)
    {
      continue;
    }

    if (!threadID)
    {
      this->UpdateProgress((double)j / this->ImageInUseSize[1]);
      if (renWin->CheckAbortStatus())
      {
        break;
      }
    }
    else if (renWin->GetAbortRender())
    {
      break;
    }

    ucptr = this->Image + 4 * j * this->ImageMemorySize[0];

    for (i = 0; i < this->ImageInUseSize[0]; i++)
    {
      int x = i + this->ImageOrigin[0];
      int y = j + this->ImageOrigin[1];

      double bounds[2] = { 0.0, 1.0 };
      float color[4] = { 0.0f, 0.0f, 0.0f, 0.0f };

      if (this->ZBuffer)
      {
        bounds[1] = this->GetZBufferValue(x, y);
      }

      iterator->SetBounds(bounds);
      iterator->Initialize(x, y);

      vtkIdType numIntersections;
      do
      {
        if (this->CellScalars)
        {
          numIntersections = iterator->GetNextIntersections(
            intersectedCells, intersectionLengths, nullptr, nullptr, nullptr);
          nearIntersections->SetNumberOfComponents(this->Scalars->GetNumberOfComponents());
          nearIntersections->SetNumberOfTuples(numIntersections);
          switch (this->Scalars->GetDataType())
          {
            vtkTemplateMacro(vtkUGVRCMLookupCopy((const VTK_TT*)this->Scalars->GetVoidPointer(0),
              (VTK_TT*)nearIntersections->GetVoidPointer(0), intersectedCells->GetPointer(0),
              this->Scalars->GetNumberOfComponents(), numIntersections));
          }
        }
        else
        {
          numIntersections = iterator->GetNextIntersections(
            nullptr, intersectionLengths, this->Scalars, nearIntersections, farIntersections);
        }
        if (numIntersections < 1)
          break;
        this->RealRayIntegrator->Integrate(
          intersectionLengths, nearIntersections, farIntersections, color);
      } while (color[3] < 0.99);

      if (color[3] > 0.0)
      {
        int val;
        val = static_cast<int>(color[0] * 255.0);
        val = (val > 255) ? (255) : (val);
        val = (val < 0) ? (0) : (val);
        ucptr[0] = static_cast<unsigned char>(val);

        val = static_cast<int>(color[1] * 255.0);
        val = (val > 255) ? (255) : (val);
        val = (val < 0) ? (0) : (val);
        ucptr[1] = static_cast<unsigned char>(val);

        val = static_cast<int>(color[2] * 255.0);
        val = (val > 255) ? (255) : (val);
        val = (val < 0) ? (0) : (val);
        ucptr[2] = static_cast<unsigned char>(val);

        val = static_cast<int>(color[3] * 255.0);
        val = (val > 255) ? (255) : (val);
        val = (val < 0) ? (0) : (val);
        ucptr[3] = static_cast<unsigned char>(val);
      }
      else
      {
        ucptr[0] = 0;
        ucptr[1] = 0;
        ucptr[2] = 0;
        ucptr[3] = 0;
      }
      ucptr += 4;
    }
  }
}

double vtkUnstructuredGridVolumeRayCastMapper::GetMinimumBoundsDepth(
  vtkRenderer* ren, vtkVolume* vol)
{
  double bounds[6];
  vol->GetBounds(bounds);

  vtkTransform* perspectiveTransform = vtkTransform::New();
  vtkMatrix4x4* perspectiveMatrix = vtkMatrix4x4::New();

  ren->ComputeAspect();
  double* aspect = ren->GetAspect();

  // Get the view matrix in two steps - there is a one step method in camera
  // but it turns off stereo so we do not want to use that one
  vtkCamera* cam = ren->GetActiveCamera();
  perspectiveTransform->Identity();
  perspectiveTransform->Concatenate(
    cam->GetProjectionTransformMatrix(aspect[0] / aspect[1], 0.0, 1.0));
  perspectiveTransform->Concatenate(cam->GetViewTransformMatrix());
  perspectiveMatrix->DeepCopy(perspectiveTransform->GetMatrix());

  double minZ = 1.0;

  for (int k = 0; k < 2; k++)
  {
    for (int j = 0; j < 2; j++)
    {
      for (int i = 0; i < 2; i++)
      {
        double inPoint[4];
        inPoint[0] = bounds[i];
        inPoint[1] = bounds[2 + j];
        inPoint[2] = bounds[4 + k];
        inPoint[3] = 1.0;

        double outPoint[4];
        perspectiveMatrix->MultiplyPoint(inPoint, outPoint);
        double testZ = outPoint[2] / outPoint[3];
        minZ = (testZ < minZ) ? (testZ) : (minZ);
      }
    }
  }

  perspectiveTransform->Delete();
  perspectiveMatrix->Delete();

  return minZ;
}

double vtkUnstructuredGridVolumeRayCastMapper::GetZBufferValue(int x, int y)
{
  int xPos, yPos;

  xPos = static_cast<int>(static_cast<float>(x) * this->ImageSampleDistance);
  yPos = static_cast<int>(static_cast<float>(y) * this->ImageSampleDistance);

  xPos = (xPos >= this->ZBufferSize[0]) ? (this->ZBufferSize[0] - 1) : (xPos);
  yPos = (yPos >= this->ZBufferSize[1]) ? (this->ZBufferSize[1] - 1) : (yPos);

  return *(this->ZBuffer + yPos * this->ZBufferSize[0] + xPos);
}

// Print method for vtkUnstructuredGridVolumeRayCastMapper
void vtkUnstructuredGridVolumeRayCastMapper::PrintSelf(ostream& os, vtkIndent indent)
{
  this->Superclass::PrintSelf(os, indent);

  os << indent << "Image Sample Distance: " << this->ImageSampleDistance << "\n";
  os << indent << "Minimum Image Sample Distance: " << this->MinimumImageSampleDistance << "\n";
  os << indent << "Maximum Image Sample Distance: " << this->MaximumImageSampleDistance << "\n";
  os << indent << "Auto Adjust Sample Distances: " << this->AutoAdjustSampleDistances << "\n";
  os << indent << "Intermix Intersecting Geometry: "
     << (this->IntermixIntersectingGeometry ? "On\n" : "Off\n");

  os << indent << "Number Of Threads: " << this->NumberOfThreads << "\n";

  if (this->RayCastFunction)
  {
    os << indent << "RayCastFunction: " << this->RayCastFunction->GetClassName() << "\n";
  }
  else
  {
    os << indent << "RayCastFunction: (none)\n";
  }

  if (this->RayIntegrator)
  {
    os << indent << "RayIntegrator: " << this->RayIntegrator->GetClassName() << endl;
  }
  else
  {
    os << indent << "RayIntegrator: (automatic)" << endl;
  }

  // Do not want to print this->ImageOrigin, this->ImageViewportSize or
  // this->ImageInUseSize since these are just internal variables with Get
  // methods for access from the ray cast function (not part of the public
  // API)
}