Function StreamingFindMinMax

Rendering/LICOpenGL2/vtkLineIntegralConvolution2D.cxx:782–828

Description find min/max of unmasked fragments across all regions download each search each region individually

// find min/max of unmasked fragments across all regions
// download each search each region individually
void StreamingFindMinMax(vtkOpenGLFramebufferObject* fbo, vtkTextureObject* tex,
  const deque<vtkPixelExtent>& extents, float& min, float& max)
{
  size_t nExtents = extents.size();
  // initiate download of each region
  fbo->AddColorAttachment(0U, tex);
  fbo->ActivateDrawBuffer(0U);
  fbo->ActivateReadBuffer(0U);
  fbo->CheckFrameBufferStatus(GL_FRAMEBUFFER);
  vector<vtkPixelBufferObject*> pbos(nExtents, nullptr);
  for (size_t q = 0; q < nExtents; ++q)
  {
    pbos[q] =
      fbo->Download(const_cast<int*>(extents[q].GetData()), VTK_FLOAT, 4, GL_FLOAT, GL_RGBA);
  }
  fbo->DeactivateDrawBuffers();
  fbo->DeactivateReadBuffer();
  fbo->RemoveColorAttachment(0U);
  fbo->RemoveColorAttachment(0U);
  // search each region
  for (size_t q = 0; q < nExtents; ++q)
  {
    vtkPixelBufferObject*& pbo = pbos[q];
    float* pColors = (float*)pbo->MapPackedBuffer();

    size_t n = extents[q].Size();
    for (size_t i = 0; i < n; ++i)
    {
      bool masked = pColors[4 * i + 1] != 0.0f;
      bool ceskip = pColors[4 * i + 2] != 0.0f;
      if (!masked && !ceskip)
      {
        float color = pColors[4 * i];
        min = min > color ? color : min;
        max = max < color ? color : max;
      }
    }

    pbo->UnmapPackedBuffer();
    pbo->Delete();
    pbo = nullptr;
  }
  pbos.clear();
#if vtkLineIntegralConvolution2DDEBUG >= 1
  std::cerr << "min=" << min << " max=" << max << endl;
#endif
}
#else
// Description
// find min/max of unmasked fragments across all regions