Create VBO to support multitextures. Write byte after byte

vtkOpenGLVertexBufferObject.cxx

//-----------------------------------------------------------------------------
void vtkOpenGLVertexBufferObject::AddDataArray(vtkDataArray *data)
{
  if (!this->VertexCount)
    {
    this->VertexCount = data->GetNumberOfTuples();
    }
  else if (VertexCount != data->GetNumberOfTuples())
    {
    vtkErrorMacro("AddDataArray() can not add array with a different number of "
                  << "tuples than previously added arrays:\n"
                  << "Should be "<< this->VertexCount << " tuples, got "
                  << data->GetNumberOfTuples() << " instead.");
    return;
    }

  this->DataArrays.push_back(data);
  this->Offset[data->GetName()] = this->Stride;
  this->Components[data->GetName()] = data->GetNumberOfComponents();
  this->DataType[data->GetName()] = data->GetDataType();
  this->Stride += data->GetDataTypeSize() * data->GetNumberOfComponents();
}

//-----------------------------------------------------------------------------
void vtkOpenGLVertexBufferObject::CreateVBO()
{
  // Resize VBO and set up iterator
  this->_PackedVBO.resize(this->Stride * this->VertexCount);
  std::vector<unsigned char>::iterator it = this->_PackedVBO.begin();

  // Fill VBO
  for (vtkIdType i = 0; i < this->VertexCount; ++i) // For each vertex
  for (int j = 0; j < this->DataArrays.size(); ++j) // For each data array (position, normals, texture, ...)
    {
    vtkDataArray* data = this->DataArrays.at(j);
    unsigned char* dataPtr = reinterpret_cast<unsigned char*>
      (data->GetVoidPointer(i * data->GetNumberOfComponents()));
    for (int k = 0; k < data->GetNumberOfComponents(); ++k) // For each component (X,Y,Z; U,V; R,G,B,A...)
    for (int l = 0; l < data->GetDataTypeSize(); ++l)       // For each byte (float:4, char:1, ...)
      {
      *(it++) = *(dataPtr++);
      }
    }

  // Upload & Reset
  this->Upload(this->_PackedVBO, vtkOpenGLBufferObject::ArrayBuffer);
  this->_PackedVBO.resize(0);
}