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

  Program:   Visualization Toolkit
  Module:    vtkOpenGLImageSliceMapper.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 "vtkOpenGLImageSliceMapper.h"

#include "vtkObjectFactory.h"
#include "vtkImageData.h"
#include "vtkImageSlice.h"
#include "vtkImageProperty.h"
#include "vtkDataArray.h"
#include "vtkLookupTable.h"
#include "vtkPoints.h"
#include "vtkMatrix4x4.h"
#include "vtkMath.h"
#include "vtkMapper.h"
#include "vtkOpenGLCamera.h"
#include "vtkOpenGLRenderer.h"
#include "vtkOpenGLRenderWindow.h"
#include "vtkOpenGLExtensionManager.h"
#include "vtkTimerLog.h"
#include "vtkGarbageCollector.h"
#include "vtkTemplateAliasMacro.h"

#include <math.h>

#include "vtkOpenGL.h"
#include "vtkgl.h" // vtkgl namespace

#ifndef VTK_IMPLEMENT_MESA_CXX
vtkStandardNewMacro(vtkOpenGLImageSliceMapper);
#endif

//----------------------------------------------------------------------------
// Initializes an instance, generates a unique index.
vtkOpenGLImageSliceMapper::vtkOpenGLImageSliceMapper()
{
  this->TextureIndex = 0;
  this->BackgroundTextureIndex = 0;
  this->FragmentShaderIndex = 0;
  this->RenderWindow = 0;
  this->TextureSize[0] = 0;
  this->TextureSize[1] = 0;
  this->TextureBytesPerPixel = 1;

  this->LastOrientation = -1;
  this->LastSliceNumber = VTK_INT_MAX;

  this->LoadCount = 0;

  this->UseClampToEdge = false;
  this->UsePowerOfTwoTextures = true;

  // Use GL_ARB_fragment_program, which is an extension to OpenGL 1.3
  // that is compatible with very old drivers and hardware, and is still
  // fully supported on modern hardware.  The only caveat is that it is
  // automatically disabled if any modern shaders (e.g. depth peeling)
  // are simultaneously loaded, so it will not interfere with them.
  this->UseFragmentProgram = false;
}

//----------------------------------------------------------------------------
vtkOpenGLImageSliceMapper::~vtkOpenGLImageSliceMapper()
{
  this->RenderWindow = NULL;
}

//----------------------------------------------------------------------------
// Release the graphics resources used by this texture.
void vtkOpenGLImageSliceMapper::ReleaseGraphicsResources(vtkWindow *renWin)
{
  if (this->TextureIndex && renWin && renWin->GetMapped())
    {
    static_cast<vtkRenderWindow *>(renWin)->MakeCurrent();
#ifdef GL_VERSION_1_1
    // free any textures
    if (glIsTexture(this->TextureIndex))
      {
      GLsizei n = 1;
      GLuint tempIndex[2];
      tempIndex[0] = this->TextureIndex;
      tempIndex[1] = this->BackgroundTextureIndex;
      // NOTE: Sun's OpenGL seems to require disabling of texture
      // before deletion
      glDisable(GL_TEXTURE_2D);
      if (glIsTexture(this->BackgroundTextureIndex))
        {
        n = 2;
        }
      glDeleteTextures(n, tempIndex);
      }
    if (this->UseFragmentProgram &&
        vtkgl::IsProgramARB(this->FragmentShaderIndex))
      {
      GLuint tempIndex;
      tempIndex = this->FragmentShaderIndex;
      glDisable(vtkgl::FRAGMENT_PROGRAM_ARB);
      vtkgl::DeleteProgramsARB(1, &tempIndex);
      }
#else
    if (glIsList(this->TextureIndex))
      {
      glDeleteLists(this->TextureIndex,1);
      }
    if (glIsList(this->BackgroundTextureIndex))
      {
      glDeleteLists(this->BackgroundTextureIndex,1);
      }
#endif
    this->TextureSize[0] = 0;
    this->TextureSize[1] = 0;
    this->TextureBytesPerPixel = 1;
    }
  this->TextureIndex = 0;
  this->BackgroundTextureIndex = 0;
  this->FragmentShaderIndex = 0;
  this->RenderWindow = NULL;
  this->Modified();
}

//----------------------------------------------------------------------------
// Subdivide the image until the pieces fit into texture memory
void vtkOpenGLImageSliceMapper::RecursiveRenderTexturedPolygon(
  vtkRenderer *ren, vtkImageProperty *property,
  vtkImageData *input, int extent[6], bool recursive)
{
  int xdim, ydim;
  int imageSize[2];
  int textureSize[2];

  // compute image size and texture size from extent
  this->ComputeTextureSize(
    extent, xdim, ydim, imageSize, textureSize);

  // Check if we can fit this texture in memory
  if (this->TextureSizeOK(textureSize))
    {
    // We can fit it - render
    this->RenderTexturedPolygon(
      ren, property, input, extent, recursive);
    }

  // If the texture does not fit, then subdivide and render
  // each half.  Unless the graphics card couldn't handle
  // a texture a small as 256x256, because if it can't handle
  // that, then something has gone horribly wrong.
  else if (textureSize[0] > 256 || textureSize[1] > 256)
    {
    int subExtent[6];
    subExtent[0] = extent[0]; subExtent[1] = extent[1];
    subExtent[2] = extent[2]; subExtent[3] = extent[3];
    subExtent[4] = extent[4]; subExtent[5] = extent[5];

    // Which is larger, x or y?
    int idx = ydim;
    int tsize = textureSize[1];
    if (textureSize[0] > textureSize[1])
      {
      idx = xdim;
      tsize = textureSize[0];
      }

    // Divide size by two
    tsize /= 2;

    // Render each half recursively
    subExtent[idx*2] = extent[idx*2];
    subExtent[idx*2 + 1] = extent[idx*2] + tsize - 1;
    this->RecursiveRenderTexturedPolygon(
      ren, property, input, subExtent, true);

    subExtent[idx*2] = subExtent[idx*2] + tsize;
    subExtent[idx*2 + 1] = extent[idx*2 + 1];
    this->RecursiveRenderTexturedPolygon(
      ren, property, input, subExtent, true);
    }
}

//----------------------------------------------------------------------------
// Load the given image extent into a texture and render it
void vtkOpenGLImageSliceMapper::RenderTexturedPolygon(
  vtkRenderer *ren, vtkImageProperty *property,
  vtkImageData *input, int extent[6], bool recursive)
{
  // get the previous texture load time
  unsigned long loadTime = this->LoadTime.GetMTime();

  // the render window, needed for state information
  vtkOpenGLRenderWindow *renWin =
    static_cast<vtkOpenGLRenderWindow *>(ren->GetRenderWindow());

#ifdef GL_VERSION_1_1
  bool reuseTexture = true;
#else
  bool reuseTexture = false;
#endif

  // if context has changed, verify context capabilities
  if (renWin != this->RenderWindow ||
      renWin->GetContextCreationTime() > loadTime)
    {
    // force two initial loads for each new context
    this->LoadCount = 0;
    this->CheckOpenGLCapabilities(renWin);
    reuseTexture = false;
    }

  // get information about the image
  int xdim, ydim; // orientation of texture wrt input image
  vtkImageSliceMapper::GetDimensionIndices(this->Orientation, xdim, ydim);

  // check whether to use a shader for bicubic interpolation
  bool checkerboard = (property && property->GetCheckerboard());
  bool cubicInterpolation = (property &&
    property->GetInterpolationType() == VTK_CUBIC_INTERPOLATION);
  bool useFragmentProgram =
    (this->UseFragmentProgram &&
     (!this->ExactPixelMatch || !this->SliceFacesCamera) &&
     (cubicInterpolation || checkerboard));

  // verify that the orientation and slice has not changed
  bool orientationChanged = (this->Orientation != this->LastOrientation);
  this->LastOrientation = this->Orientation;
  bool sliceChanged = (this->SliceNumber != this->LastSliceNumber);
  this->LastSliceNumber = this->SliceNumber;

  // get the mtime of the property, including the lookup table
  unsigned long propertyMTime = 0;
  if (property)
    {
    propertyMTime = property->GetMTime();
    if (!this->PassColorData)
      {
      vtkScalarsToColors *table = property->GetLookupTable();
      if (table)
        {
        unsigned long mtime = table->GetMTime();
        if (mtime > propertyMTime)
          {
          propertyMTime = mtime;
          }
        }
      }
    }

  // need to reload the texture
  if (this->vtkImageMapper3D::GetMTime() > loadTime ||
      propertyMTime > loadTime ||
      input->GetMTime() > loadTime ||
      orientationChanged || sliceChanged ||
      this->LoadCount < 2 || recursive)
    {
    this->LoadCount++;

    // get the data to load as a texture
    int xsize = this->TextureSize[0];
    int ysize = this->TextureSize[1];
    int bytesPerPixel = this->TextureBytesPerPixel;

    // whether to try to use the input data directly as the texture
    bool reuseData = true;

    // generate the data to be used as a texture
    unsigned char *data = this->MakeTextureData(
      (this->PassColorData ? 0 : property), input, extent, xsize, ysize,
      bytesPerPixel, reuseTexture, reuseData);

    GLuint tempIndex[2];
    tempIndex[0] = 0;
    tempIndex[1] = 0;

#ifdef GL_VERSION_1_1
    if (reuseTexture)
      {
      glBindTexture(GL_TEXTURE_2D, this->TextureIndex);
      }
    else
#endif
      {
      // free any old display lists
      this->ReleaseGraphicsResources(renWin);
      this->RenderWindow = renWin;

      // define a display list for this texture
      // get a unique display list id
#ifdef GL_VERSION_1_1
      GLsizei ntex = 1 + (this->Background != 0);
      glGenTextures(ntex, tempIndex);
      this->TextureIndex = static_cast<long>(tempIndex[0]);
      this->BackgroundTextureIndex = static_cast<long>(tempIndex[1]);
      glBindTexture(GL_TEXTURE_2D, this->TextureIndex);
#else
      this->TextureIndex = glGenLists(1);
      if (this->Background)
        {
        this->BackgroundTextureIndex = glGenLists(1);
        }
      glNewList(static_cast<GLuint>(this->TextureIndex), GL_COMPILE);
#endif

      renWin->RegisterTextureResource(this->TextureIndex);
      if (this->Background)
        {
        renWin->RegisterTextureResource(this->BackgroundTextureIndex);
        }
      }

    GLenum interp = GL_LINEAR;
    if (property->GetInterpolationType() == VTK_NEAREST_INTERPOLATION &&
        !this->ExactPixelMatch)
      {
      interp = GL_NEAREST;
      }

    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, interp);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, interp);

    GLenum wrap = (this->UseClampToEdge ? vtkgl::CLAMP_TO_EDGE : GL_CLAMP);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, wrap);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, wrap);

    GLenum format = GL_LUMINANCE;
    int internalFormat = bytesPerPixel;
    switch (bytesPerPixel)
      {
      case 1: format = GL_LUMINANCE; break;
      case 2: format = GL_LUMINANCE_ALPHA; break;
      case 3: format = GL_RGB; break;
      case 4: format = GL_RGBA; break;
      }

#ifdef GL_VERSION_1_1
    // if we are using OpenGL 1.1, force 32 bit textures
    switch (bytesPerPixel)
      {
      case 1: internalFormat = GL_LUMINANCE8; break;
      case 2: internalFormat = GL_LUMINANCE8_ALPHA8; break;
      case 3: internalFormat = GL_RGB8; break;
      case 4: internalFormat = GL_RGBA8; break;
      }
#endif

    if (useFragmentProgram && this->FragmentShaderIndex == 0)
      {
      // Use the the ancient ARB_fragment_program extension, it works
      // reliably even with very old hardware and drivers
      vtkgl::GenProgramsARB(1, tempIndex);
      this->FragmentShaderIndex = static_cast<long>(tempIndex[0]);
      vtkStdString prog = this->BuildFragmentProgram(property);

      vtkgl::BindProgramARB(vtkgl::FRAGMENT_PROGRAM_ARB,
                            this->FragmentShaderIndex);

      vtkgl::ProgramStringARB(vtkgl::FRAGMENT_PROGRAM_ARB,
                              vtkgl::PROGRAM_FORMAT_ASCII_ARB,
                              static_cast<GLsizei>(prog.size()), prog.c_str());

      GLint erri;
      glGetIntegerv(vtkgl::PROGRAM_ERROR_POSITION_ARB, &erri);
      if (erri != -1)
        {
        vtkErrorMacro("Failed to load bicubic shader program: "
                      << reinterpret_cast<const char *>(
                           glGetString(vtkgl::PROGRAM_ERROR_STRING_ARB)));
        }
      }

#ifdef GL_VERSION_1_1
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);

    if (reuseTexture)
      {
      glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0,
                      xsize, ysize, format, GL_UNSIGNED_BYTE,
                      static_cast<const GLvoid *>(data));
      }
    else
#endif
      {
      glTexImage2D(GL_TEXTURE_2D, 0, internalFormat,
                   xsize, ysize, 0, format,
                   GL_UNSIGNED_BYTE, static_cast<const GLvoid *>(data));
      this->TextureSize[0] = xsize;
      this->TextureSize[1] = ysize;
      this->TextureBytesPerPixel = bytesPerPixel;
      }

#ifndef GL_VERSION_1_1
    glEndList();
#endif

    if (!reuseData)
      {
      delete [] data;
      }

    if (this->Background)
      {
      double color[4];
      this->GetBackgroundColor(property, color);
      unsigned char ccolor[4];
      ccolor[0] = static_cast<unsigned char>(255*color[0] + 0.5);
      ccolor[1] = static_cast<unsigned char>(255*color[1] + 0.5);
      ccolor[2] = static_cast<unsigned char>(255*color[2] + 0.5);
      ccolor[3] = static_cast<unsigned char>(255*color[3] + 0.5);
      if (bytesPerPixel == 2)
        {
        ccolor[1] = ccolor[3];
        }
      unsigned char bgdata[64];
      unsigned char *bgdatap = bgdata;
      for (int ii = 0; ii < 16; ii++)
        {
        for (int jj = 0; jj < bytesPerPixel; jj++)
          {
          bgdatap[jj] = ccolor[jj];
          }
        bgdatap += bytesPerPixel;
        }

#ifdef GL_VERSION_1_1
      glBindTexture(GL_TEXTURE_2D, this->BackgroundTextureIndex);
#else
      glNewList(static_cast<GLuint>(this->BackgroundTextureIndex),
                GL_COMPILE);
#endif

      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
      glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
      glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
      glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
      glTexImage2D(GL_TEXTURE_2D, 0, internalFormat,
                   4, 4, 0, format, GL_UNSIGNED_BYTE,
                   static_cast<const GLvoid *>(bgdata));

#ifndef GL_VERSION_1_1
      glEndList();
#endif
      }

    // modify the load time to the current time
    this->LoadTime.Modified();
    }

  // execute the display list that uses creates the texture
#ifdef GL_VERSION_1_1
  glBindTexture(GL_TEXTURE_2D, this->TextureIndex);
#else
  glCallList(static_cast<GLuint>(this->TextureIndex));
#endif

  if (useFragmentProgram)
    {
    this->BindFragmentProgram(ren, property);

    glEnable(vtkgl::FRAGMENT_PROGRAM_ARB);
    }

  glEnable(GL_TEXTURE_2D);

  // modulate the texture with the fragment for lighting effects
  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

  vtkPoints *points = this->Points;
  if (this->ExactPixelMatch && this->SliceFacesCamera)
    {
    points = 0;
    }

  this->RenderPolygon(points, extent, true);

  if (this->Background)
    {
#ifdef GL_VERSION_1_1
    glBindTexture(GL_TEXTURE_2D, this->BackgroundTextureIndex);
#else
    glCallList(static_cast<GLuint>(this->BackgroundTextureIndex));
#endif

    this->RenderBackground(points, extent, true);
    }

  if (useFragmentProgram)
    {
    glDisable(vtkgl::FRAGMENT_PROGRAM_ARB);
    }
}

//----------------------------------------------------------------------------
// Render the polygon that displays the image data
void vtkOpenGLImageSliceMapper::RenderPolygon(
  vtkPoints *points, const int extent[6], bool textured)
{
  static double normals[3][3] =
    { { 1.0, 0.0, 0.0 }, { 0.0, -1.0, 0.0 }, { 0.0, 0.0, 1.0 } };
  double *normal = normals[(this->Orientation % 3)];

  if (!points)
    {
    double coords[12], tcoords[8];
    this->MakeTextureGeometry(extent, coords, tcoords);
    double *coord = coords;
    double *tcoord = tcoords;

    glBegin(GL_POLYGON);
    for (int i = 0; i < 4; i++)
      {
      glNormal3dv(normal);
      if (textured)
        {
        glTexCoord2dv(tcoord);
        }
      glVertex3dv(coord);

      coord += 3;
      tcoord += 2;
      }
    glEnd();
    }
  else if (points->GetNumberOfPoints())
    {
    int xdim, ydim;
    vtkImageSliceMapper::GetDimensionIndices(this->Orientation, xdim, ydim);
    double *origin = this->DataOrigin;
    double *spacing = this->DataSpacing;
    double xshift = origin[xdim] - (0.5 - extent[2*xdim])*spacing[xdim];
    double xscale = this->TextureSize[xdim]*spacing[xdim];
    double yshift = origin[ydim] - (0.5 - extent[2*ydim])*spacing[ydim];
    double yscale = this->TextureSize[ydim]*spacing[ydim];
    vtkIdType ncoords = points->GetNumberOfPoints(); 
    double coord[3];
    double tcoord[2];

    glBegin(GL_POLYGON);
    for (vtkIdType i = 0; i < ncoords; i++)
      {
      points->GetPoint(i, coord);
      glNormal3dv(normal);
      if (textured)
        {
        tcoord[0] = (coord[0] - xshift)/xscale;
        tcoord[1] = (coord[1] - yshift)/yscale;
        glTexCoord2dv(tcoord);
        }
      glVertex3dv(coord);
      }
    glEnd();
    }
}

//----------------------------------------------------------------------------
// Render a wide black border around the polygon, wide enough to fill
// the entire viewport.
void vtkOpenGLImageSliceMapper::RenderBackground(
  vtkPoints *points, const int extent[6], bool textured)
{
  static double borderThickness = 1e6;
  static double normals[3][3] =
    { { 1.0, 0.0, 0.0 }, { 0.0, -1.0, 0.0 }, { 0.0, 0.0, 1.0 } };
  double *normal = normals[(this->Orientation % 3)];

  int xdim, ydim;
  vtkImageSliceMapper::GetDimensionIndices(this->Orientation, xdim, ydim);

  if (!points)
    {
    double coords[15], tcoords[10], center[3], tcenter[2];
    this->MakeTextureGeometry(extent, coords, tcoords);
    coords[12] = coords[0];
    coords[13] = coords[1];
    coords[14] = coords[2];
    tcoords[8] = tcoords[0];
    tcoords[9] = tcoords[1];

    center[0] = 0.25*(coords[0] + coords[3] + coords[6] + coords[9]);
    center[1] = 0.25*(coords[1] + coords[4] + coords[7] + coords[10]);
    center[2] = 0.25*(coords[2] + coords[5] + coords[8] + coords[11]);

    tcenter[0] = 0.25*(tcoords[0] + tcoords[2] + tcoords[4] + tcoords[6]);
    tcenter[1] = 0.25*(tcoords[1] + tcoords[3] + tcoords[5] + tcoords[7]);

    double *coord = coords;
    double *tcoord = tcoords;

    glBegin(GL_TRIANGLE_STRIP);
    for (int i = 0; i < 5; i++)
      {
      glNormal3dv(normal);
      if (textured)
        {
        glTexCoord2dv(tcoord);
        }
      glVertex3dv(coord);

      double dx = coord[xdim] - center[xdim];
      double sx = (dx >= 0 ? 1 : -1);
      double dy = coord[ydim] - center[ydim];
      double sy = (dy >= 0 ? 1 : -1);
      coord[xdim] += borderThickness*sx;
      coord[ydim] += borderThickness*sy;

      glNormal3dv(normal);
      if (textured)
        {
        tcoord[0] += (tcoord[0] - tcenter[0])/dx*sx*borderThickness;
        tcoord[1] += (tcoord[1] - tcenter[1])/dy*sy*borderThickness;
        glTexCoord2dv(tcoord);
        }
      glVertex3dv(coord);

      coord += 3;
      tcoord += 2;
      }
    glEnd();
    }
  else if (points->GetNumberOfPoints())
    {
    double *origin = this->DataOrigin;
    double *spacing = this->DataSpacing;
    double xshift = origin[xdim] - (0.5 - extent[2*xdim])*spacing[xdim];
    double xscale = this->TextureSize[xdim]*spacing[xdim];
    double yshift = origin[ydim] - (0.5 - extent[2*ydim])*spacing[ydim];
    double yscale = this->TextureSize[ydim]*spacing[ydim];

    vtkIdType ncoords = points->GetNumberOfPoints();
    double coord[3], coord1[3], tcoord[2];

    points->GetPoint(ncoords-1, coord1);
    points->GetPoint(0, coord);
    double dx0 = coord[0] - coord1[0];
    double dy0 = coord[1] - coord1[1];
    double r = sqrt(dx0*dx0 + dy0*dy0);
    dx0 /= r;
    dy0 /= r;

    glBegin(GL_TRIANGLE_STRIP);
    for (vtkIdType i = 0; i <= ncoords; i++)
      {
      glNormal3dv(normal);
      if (textured)
        {
        tcoord[0] = (coord[0] - xshift)/xscale;
        tcoord[1] = (coord[1] - yshift)/yscale;
        glTexCoord2dv(tcoord);
        }
      glVertex3dv(coord);

      points->GetPoint(((i + 1) % ncoords), coord1);
      double dx1 = coord1[0] - coord[0];
      double dy1 = coord1[1] - coord[1];
      r = sqrt(dx1*dx1 + dy1*dy1);
      dx1 /= r;
      dy1 /= r;

      double t;
      if (fabs(dx0 + dx1) > fabs(dy0 + dy1))
        {
        t = (dy1 - dy0)/(dx0 + dx1);
        }
      else
        {
        t = (dx0 - dx1)/(dy0 + dy1);
        }
      coord[0] += (t*dx0 + dy0)*borderThickness;
      coord[1] += (t*dy0 - dx0)*borderThickness;

      glNormal3dv(normal);
      if (textured)
        {
        tcoord[0] = (coord[0] - xshift)/xscale;
        tcoord[1] = (coord[1] - yshift)/yscale;
        glTexCoord2dv(tcoord);
        }
      glVertex3dv(coord);

      coord[0] = coord1[0];
      coord[1] = coord1[1];
      dx0 = dx1;
      dy0 = dy1;
      }
    glEnd();
    }
}

//----------------------------------------------------------------------------
void vtkOpenGLImageSliceMapper::BindFragmentProgram(
  vtkRenderer *ren, vtkImageProperty *property)
{
  int xdim, ydim, zdim; // orientation of texture wrt input image
  vtkImageSliceMapper::GetDimensionIndices(this->Orientation, xdim, ydim);
  zdim = 3 - xdim - ydim; // they sum to three
  double *spacing = this->DataSpacing;
  double *origin = this->DataOrigin;
  int *extent = this->DisplayExtent;

  // Bind the bicubic interpolation fragment program, it will
  // not do anything if modern shader objects are also in play.
  vtkgl::BindProgramARB(vtkgl::FRAGMENT_PROGRAM_ARB,
                        this->FragmentShaderIndex);

  // checkerboard information
  double checkSpacing[2], checkOffset[2];
  property->GetCheckerboardSpacing(checkSpacing);
  property->GetCheckerboardOffset(checkOffset);

  // transformation to permute texture-oriented coords to data coords
  double mat[16];
  vtkMatrix4x4::Identity(mat);
  mat[0] = mat[5] = mat[10] = 0.0;
  mat[4*xdim] = mat[1+4*ydim] = 1.0;
  int dimsep = ydim - xdim + 3*(xdim > ydim);
  mat[2+4*zdim] = (((dimsep % 3) == 1) ? 1.0 : -1.0);
  mat[4*zdim+3] = origin[zdim] + spacing[zdim]*extent[2*zdim];

  // checkerboard uses view coordinates
  vtkMatrix4x4 *m = this->GetDataToWorldMatrix();
  vtkMatrix4x4 *c = ren->GetActiveCamera()->GetViewTransformMatrix();
  vtkMatrix4x4::Multiply4x4(*m->Element, mat, mat);
  vtkMatrix4x4::Multiply4x4(*c->Element, mat, mat);

  // first parameter: texture size needed for bicubic interpolator
  vtkgl::ProgramLocalParameter4fARB(vtkgl::FRAGMENT_PROGRAM_ARB, 0,
    static_cast<float>(this->TextureSize[0]),
    static_cast<float>(this->TextureSize[1]),
    static_cast<float>(1.0/this->TextureSize[0]),
    static_cast<float>(1.0/this->TextureSize[1]));

  // second parameter: scale and offset for converting texture coords
  // into the input image's data coords
  vtkgl::ProgramLocalParameter4fARB(vtkgl::FRAGMENT_PROGRAM_ARB, 1,
    static_cast<float>(this->TextureSize[0]*spacing[xdim]),
    static_cast<float>(this->TextureSize[1]*spacing[ydim]),
    static_cast<float>(origin[xdim] +
                       spacing[xdim]*(extent[2*xdim] - 0.5)),
    static_cast<float>(origin[ydim] +
                       spacing[ydim]*(extent[2*ydim] - 0.5)));

  // third parameter: scale and offset for converting data coords into
  // checkboard square indices, for checkerboarding
  vtkgl::ProgramLocalParameter4fARB(vtkgl::FRAGMENT_PROGRAM_ARB, 2,
    static_cast<float>(0.5/checkSpacing[0]),
    static_cast<float>(0.5/checkSpacing[1]),
    static_cast<float>(-0.5*checkOffset[0]),
    static_cast<float>(-0.5*checkOffset[1]));

  // fourth, fifth param: first two rows of the transformation matrix
  // from data coords to camera coords (including a pre-translation of
  // z from zero to the z position of the slice, since the texture coords
  // are 2D and do not provide the z position)
  vtkgl::ProgramLocalParameter4fARB(vtkgl::FRAGMENT_PROGRAM_ARB, 3,
    static_cast<float>(mat[0]), static_cast<float>(mat[1]),
    static_cast<float>(mat[2]), static_cast<float>(mat[3]));
  vtkgl::ProgramLocalParameter4fARB(vtkgl::FRAGMENT_PROGRAM_ARB, 4,
    static_cast<float>(mat[4]), static_cast<float>(mat[5]),
    static_cast<float>(mat[6]), static_cast<float>(mat[7]));
}

//----------------------------------------------------------------------------
vtkStdString vtkOpenGLImageSliceMapper::BuildFragmentProgram(
  vtkImageProperty *property)
{
  vtkStdString prog = 
    "!!ARBfp1.0\n"
    "\n";

  // parameters needed for cubic interpolation:
  // texdim is texture size {width, height, 1.0/width, 1.0/height}
  // parameters needed for checkerboarding:
  // todata is for converting tex coords to VTK data coords
  // togrid converts transformed data coords to checkerboard squares
  // mx, my are first two rows of matrix for transforming data coords
  prog.append(
    "PARAM texdim = program.local[0];\n"
    "PARAM todata = program.local[1];\n"
    "PARAM togrid = program.local[2];\n"
    "PARAM mx = program.local[3];\n"
    "PARAM my = program.local[4];\n"
    "TEMP coord, coord2;\n"
    "TEMP c, c1, c2;\n"
    "TEMP weightx, weighty;\n"
    "\n");

  // checkerboard
  if (property->GetCheckerboard())
    {
    prog.append(
    "# generate a checkerboard pattern\n"
    "MOV coord.xyzw, {0, 0, 0, 1};\n"
    "MAD coord.xy, fragment.texcoord.xyxy, todata.xyxy, todata.zwzw;\n"
    "DP4 coord2.x, coord, mx;\n"
    "DP4 coord2.y, coord, my;\n"
    "MAD coord.xy, coord2.xyxy, togrid.xyxy, togrid.zwzw;\n"
    "FRC coord.xy, coord;\n"
    "SUB coord.xy, coord, {0.5, 0.5, 0.5, 0.5};\n"
    "MUL coord.x, coord.x, coord.y;\n"
    "KIL coord.x;\n"
    "\n");
    }

  // interpolate
  if (property->GetInterpolationType() == VTK_CUBIC_INTERPOLATION)
    {
    // create a bicubic interpolation program
    prog.append(
    "# compute the {rx, ry, fx, fy} fraction vector\n"
    "MAD coord, fragment.texcoord.xyxy, texdim.xyxy, {0.5, 0.5, 0.5, 0.5};\n"
    "FRC coord, coord;\n"
    "SUB coord.xy, {1, 1, 1, 1}, coord;\n"
    "\n"
    "# compute the x weights\n"
    "MAD weightx, coord.zzxx, {0.5, 1.5, 1.5, 0.5}, {0,-1,-1, 0};\n"
    "MAD weightx, weightx, coord.xzxz, {0,-1,-1, 0};\n"
    "MUL weightx, weightx, -coord.xxzz;\n"
    "\n"
    "# compute the y weights\n"
    "MAD weighty, coord.wwyy, {0.5, 1.5, 1.5, 0.5}, {0,-1,-1, 0};\n"
    "MAD weighty, weighty, coord.ywyw, {0,-1,-1, 0};\n"
    "MUL weighty, weighty, -coord.yyww;\n"
    "\n"
    "# get the texture coords for the coefficients\n"
    "ADD coord, coord.xyxy, {-2,-2,-1,-2};\n"
    "MAD coord, coord, texdim.zwzw, fragment.texcoord.xyxy;\n"
    "MAD coord2, texdim.zwzw, {2, 0, 2, 0}, coord;\n"
    "\n");

    // loop through the rows of the kernel
    for (int i = 0; i < 4; i++)
      {
      prog.append(
        "# do a row of texture lookups and weights\n"
        "TEX c2, coord.xyzw, texture, 2D;\n"
        "MUL c1, c2, weightx.xxxx;\n"
        "TEX c2, coord.zwxy, texture, 2D;\n"
        "MAD c1, c2, weightx.yyyy, c1;\n"
        "TEX c2, coord2.xyzw, texture, 2D;\n"
        "MAD c1, c2, weightx.zzzz, c1;\n"
        "TEX c2, coord2.zwxy, texture, 2D;\n"
        "MAD c1, c2, weightx.wwww, c1;\n");

      // choose the y weight for current row
      static const char *rowsum[4] = {
        "MUL c, weighty.xxxx, c1;\n\n",
        "MAD c, weighty.yyyy, c1, c;\n\n",
        "MAD c, weighty.zzzz, c1, c;\n\n",
        "MAD c, weighty.wwww, c1, c;\n\n"
        };

      prog.append(rowsum[i]);

      if (i < 3)
        {
        prog.append(
        "# advance y coord to next row\n"
        "ADD coord.yw, coord, texdim.wwww;\n"
        "ADD coord2.yw, coord2, texdim.wwww;\n"
        "\n");
        }
      }
    }
  else
    {
    // use currently set texture interpolation
    prog.append(
    "# interpolate the texture\n"
    "TEX c, fragment.texcoord, texture, 2D;\n"
    "\n");
    }

  // modulate the fragment color with the texture
  prog.append(
    "# output the color\n"
    "MUL result.color, fragment.color, c;\n"
    "\n");

  // end program
  prog.append(
    "END\n");

  return prog;
}

//----------------------------------------------------------------------------
void vtkOpenGLImageSliceMapper::ComputeTextureSize(
  const int extent[6], int &xdim, int &ydim,
  int imageSize[2], int textureSize[2])
{
  // find dimension indices that will correspond to the
  // columns and rows of the 2D texture
  vtkImageSliceMapper::GetDimensionIndices(this->Orientation, xdim, ydim);

  // compute the image dimensions
  imageSize[0] = (extent[xdim*2+1] - extent[xdim*2] + 1);
  imageSize[1] = (extent[ydim*2+1] - extent[ydim*2] + 1);

  if (this->UsePowerOfTwoTextures)
    {
    // find the target size of the power-of-two texture
    for (int i = 0; i < 2; i++)
      {
      int powerOfTwo = 1;
      while (powerOfTwo < imageSize[i])
        {
        powerOfTwo <<= 1;
        }
      textureSize[i] = powerOfTwo;
      }
    }
  else
    {
    textureSize[0] = imageSize[0];
    textureSize[1] = imageSize[1];
    }
}

//----------------------------------------------------------------------------
// Determine if a given texture size is supported by the video card
bool vtkOpenGLImageSliceMapper::TextureSizeOK(const int size[2])
{
#ifdef GL_VERSION_1_1
  // First ask OpenGL what the max texture size is
  GLint maxSize;
  glGetIntegerv(GL_MAX_TEXTURE_SIZE, &maxSize);
  if (size[0] > maxSize || size[1] > maxSize)
    {
    return 0;
    }

  // Test a proxy texture to see if it fits in memory
  glTexImage2D(GL_PROXY_TEXTURE_2D, 0, GL_RGBA8, size[0], size[1],
               0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
  GLint params = 0;
  glGetTexLevelParameteriv(GL_PROXY_TEXTURE_2D, 0, GL_TEXTURE_WIDTH,
                           &params);

  // if it does fit, we will render it later
  return (params == 0 ? 0 : 1);
#else
  // Otherwise we are version 1.0 and we'll just assume the card
  // can do 1024x1024
  return (size[0] <= 1024 && size[1] <= 1024);
#endif
}

//----------------------------------------------------------------------------
// Set the modelview transform and load the texture
void vtkOpenGLImageSliceMapper::Render(vtkRenderer *ren, vtkImageSlice *prop)
{
  vtkOpenGLRenderWindow *renWin =
    vtkOpenGLRenderWindow::SafeDownCast(ren->GetRenderWindow());

  if (renWin && (renWin != this->RenderWindow ||
      renWin->GetContextCreationTime() > this->LoadTime.GetMTime()))
    {
    this->CheckOpenGLCapabilities(renWin);
    }

  // time the render
  this->Timer->StartTimer();

  // update the input information
  vtkImageData *input = this->GetInput();
  input->GetSpacing(this->DataSpacing);
  input->GetOrigin(this->DataOrigin);
  input->GetWholeExtent(this->DataWholeExtent);

  // OpenGL matrices are column-order, not row-order like VTK
  vtkMatrix4x4 *matrix = this->GetDataToWorldMatrix();
  double mat[16];
  vtkMatrix4x4::Transpose(*matrix->Element, mat);

  // insert model transformation
  glMatrixMode(GL_MODELVIEW);
  glPushMatrix();
  glMultMatrixd(mat);

  // push a bunch of OpenGL state items, so they can be popped later:
  // GL_ALPHA_TEST, GL_DEPTH_TEST, GL_COLOR_MATERIAL, GL_CULL_FACE,
  // GL_LIGHTING, GL_CLIP_PLANE, GL_TEXTURE_2D
  glPushAttrib(GL_ENABLE_BIT);

  // and now enable/disable as needed for our render
  glDisable(GL_CULL_FACE);
  glDisable(GL_COLOR_MATERIAL);

  // don't accept fragments if they have zero opacity:
  // this will stop the zbuffer from being blocked by totally
  // transparent texture fragments.
  glEnable(GL_ALPHA_TEST);
  glAlphaFunc(GL_GREATER, static_cast<GLclampf>(0));

  // depth peeling
  vtkOpenGLRenderer *oRenderer = static_cast<vtkOpenGLRenderer *>(ren);

  if (oRenderer->GetDepthPeelingHigherLayer())
    {
    GLint uUseTexture = oRenderer->GetUseTextureUniformVariable();
    GLint uTexture = oRenderer->GetTextureUniformVariable();
    vtkgl::Uniform1i(uUseTexture, 1);
    vtkgl::Uniform1i(uTexture, 0); // active texture 0
    }

#ifdef GL_VERSION_1_1
  // do an offset to avoid depth buffer issues
  if (vtkMapper::GetResolveCoincidentTopology() !=
      VTK_RESOLVE_SHIFT_ZBUFFER )
    {
    double f, u;
    glEnable(GL_POLYGON_OFFSET_FILL);
    vtkMapper::GetResolveCoincidentTopologyPolygonOffsetParameters(f,u);
    glPolygonOffset(f,u);
    }
#endif

  // Add all the clipping planes
  int numClipPlanes = this->GetNumberOfClippingPlanes();
  if (numClipPlanes > 6)
    {
    vtkErrorMacro(<< "OpenGL has a limit of 6 clipping planes");
    }

  for (int i = 0; i < 6; i++)
    {
    GLenum clipPlaneId = static_cast<GLenum>(GL_CLIP_PLANE0+i);
    if (i < numClipPlanes)
      {
      double planeEquation[4];
      this->GetClippingPlaneInDataCoords(matrix, i, planeEquation);
      glClipPlane(clipPlaneId, planeEquation);
      glEnable(clipPlaneId);
      }
    else
      {
      glDisable(clipPlaneId);
      }
    }

  // Whether to write to the depth buffer and color buffer
  glDepthMask(this->DepthEnable ? GL_TRUE : GL_FALSE);
  if (!this->ColorEnable && !this->MatteEnable)
    {
    glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
    }

  // color and lighting related items
  vtkImageProperty *property = prop->GetProperty();
  double opacity = property->GetOpacity();
  double ambient = property->GetAmbient();
  double diffuse = property->GetDiffuse();

  // render the backing polygon
  int backing = property->GetBacking();
  double *bcolor = property->GetBackingColor();
  if (backing &&
      (this->MatteEnable || (this->DepthEnable && !this->ColorEnable)))
    {
    // the backing polygon is always opaque
    this->RenderColorAndLighting(
      bcolor[0], bcolor[1], bcolor[2], 1.0, ambient, diffuse);
    this->RenderPolygon(this->Points, this->DisplayExtent, false);
    if (this->Background)
      {
      this->RenderBackground(this->Points, this->DisplayExtent, false);
      }
    }

  // render the texture
  if (this->ColorEnable || (!backing && this->DepthEnable))
    {
    this->RenderColorAndLighting(1.0, 1.0, 1.0, opacity, ambient, diffuse);

    this->RecursiveRenderTexturedPolygon(
      ren, property, this->GetInput(), this->DisplayExtent, false);
    }

  // Set the masks back again
  glDepthMask(GL_TRUE);
  if (!this->ColorEnable && !this->MatteEnable)
    {
    glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
    }

  // pop the following attribs that were changed:
  // GL_ALPHA_TEST, GL_DEPTH_TEST, GL_COLOR_MATERIAL, GL_CULL_FACE,
  // GL_LIGHTING, GL_CLIP_PLANE, GL_TEXTURE_2D
  glPopAttrib();

  // pop transformation matrix
  glMatrixMode(GL_MODELVIEW);
  glPopMatrix();

  this->Timer->StopTimer();
  this->TimeToDraw = this->Timer->GetElapsedTime();
  if (this->TimeToDraw == 0)
    {
    this->TimeToDraw = 0.0001;
    }
}

//----------------------------------------------------------------------------
void vtkOpenGLImageSliceMapper::RenderColorAndLighting(
  double red, double green, double blue,
  double alpha, double ambient, double diffuse)
{
  glColor4f(red, green, blue, alpha);

  if (ambient == 1.0 && diffuse == 0.0)
    {
    glDisable(GL_LIGHTING);
    }
  else
    {
    float color[4];
    color[3] = alpha;
    glEnable(GL_LIGHTING);
    glShadeModel(GL_FLAT);
    color[0] = red*ambient;
    color[1] = green*ambient;
    color[2] = blue*ambient;
    glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, color);
    color[0] = red*diffuse;
    color[1] = green*diffuse;
    color[2] = blue*diffuse;
    glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, color);
    color[0] = color[1] = color[2] = 0.0;
    glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, color);
    }
}

//----------------------------------------------------------------------------
void vtkOpenGLImageSliceMapper::CheckOpenGLCapabilities(
  vtkOpenGLRenderWindow *renWin)
{
  vtkOpenGLExtensionManager *manager = 0;

  if (renWin)
    {
    manager = renWin->GetExtensionManager();
    }

  if (renWin && manager)
    {
    this->UseClampToEdge =
      (manager->ExtensionSupported("GL_VERSION_1_2") ||
       manager->ExtensionSupported("GL_EXT_texture_edge_clamp"));
    this->UsePowerOfTwoTextures =
      !(manager->ExtensionSupported("GL_VERSION_2_0") ||
        manager->ExtensionSupported("GL_ARB_texture_non_power_of_two"));
    this->UseFragmentProgram =
      (manager->ExtensionSupported("GL_VERSION_1_3") &&
       manager->LoadSupportedExtension("GL_ARB_fragment_program"));
    }
  else
    {
    this->UseClampToEdge = false;
    this->UsePowerOfTwoTextures = true;
    this->UseFragmentProgram = false;
    }
}

//----------------------------------------------------------------------------
void vtkOpenGLImageSliceMapper::PrintSelf(ostream& os, vtkIndent indent)
{
  this->Superclass::PrintSelf(os,indent);
}