//=============================================================================
  // d3dUtil.cpp by Frank Luna (C) 2005 All Rights Reserved.
  //=============================================================================
  
  include <d3dUtil.h>
  
  void GenTriGrid(int numVertRows, int numVertCols,
                                  float dx, float dz, 
                                  const D3DXVECTOR3& center, 
                                  std::vector<D3DXVECTOR3>& verts,
                                  std::vector<DWORD>& indices)
  {
          int numVertices = numVertRows*numVertCols;
          int numCellRows = numVertRows-1;
          int numCellCols = numVertCols-1;
  
          int numTris = numCellRows*numCellCols*2;
  
          float width = (float)numCellCols * dx;
          float depth = (float)numCellRows * dz;
  
          //===========================================
          // Build vertices.
  
          // We first build the grid geometry centered about the origin and on
          // the xz-plane, row-by-row and in a top-down fashion.  We then translate
          // the grid vertices so that they are centered about the specified 
          // parameter 'center'.
  
          verts.resize( numVertices );
  
          // Offsets to translate grid from quadrant 4 to center of 
          // coordinate system.
          float xOffset = -width * 0.5f; 
          float zOffset =  depth * 0.5f;
  
          int k = 0;
          for(float i = 0; i < numVertRows; ++i)
          {
                  for(float j = 0; j < numVertCols; ++j)
                  {
                          // Negate the depth coordinate to put in quadrant four.  
                          // Then offset to center about coordinate system.
                          verts[k].x =  j * dx + xOffset;
                          verts[k].z = -i * dz + zOffset;
                          verts[k].y =  0.0f;
  
                          // Translate so that the center of the grid is at the
                          // specified 'center' parameter.
                          D3DXMATRIX T;
                          D3DXMatrixTranslation(&T, center.x, center.y, center.z);
                          D3DXVec3TransformCoord(&verts[k], &verts[k], &T);
                          
                          ++k; // Next vertex
                  }
          }
  
          //===========================================
          // Build indices.
  
          indices.resize(numTris * 3);
           
          // Generate indices for each quad.
          k = 0;
          for(DWORD i = 0; i < (DWORD)numCellRows; ++i)
          {
                  for(DWORD j = 0; j < (DWORD)numCellCols; ++j)
                  {
                          indices[k]     =   i   * numVertCols + j;
                          indices[k + 1] =   i   * numVertCols + j + 1;
                          indices[k + 2] = (i+1) * numVertCols + j;
                                          
                          indices[k + 3] = (i+1) * numVertCols + j;
                          indices[k + 4] =   i   * numVertCols + j + 1;
                          indices[k + 5] = (i+1) * numVertCols + j + 1;
  
                          // next quad
                          k += 6;
                  }
          }
  }