《Focus On 3D Terrain Programming》中一段代码的注释二

取自《Focus On 3D Terrain Programming》中的一段:

 bool CTERRAIN::MakeTerrainFault( int iSize, int iIterations, int iMinDelta, int iMaxDelta, float fFilter )
 {
   ......
   .............
   for( iCurrentIteration=; iCurrentIteration<iIterations; iCurrentIteration++ )
   {
     //calculate the height range (linear interpolation from iMaxDelta to iMinDelta) for this fault-pass
     iHeight= iMaxDelta - ( ( iMaxDelta-iMinDelta )*iCurrentIteration )/iIterations;
 
     //pick two points at random from the entire height map
     iRandX1= rand( )%m_iSize;
     iRandZ1= rand( )%m_iSize;
 
     //check to make sure that the points are not the same
     do
     {
       iRandX2= rand( )%m_iSize;
       iRandZ2= rand( )%m_iSize;
     } while ( iRandX2==iRandX1 && iRandZ2==iRandZ1 );
 
     //iDirX1, iDirZ1 is a vector going the same direction as the line
     iDirX1= iRandX2-iRandX1;
     iDirZ1= iRandZ2-iRandZ1;
 
     for( z=; z<m_iSize; z++ )
     {
       for( x=; x<m_iSize; x++ )
       {
         //iDirX2, iDirZ2 is a vector from iRandX1, iRandZ1 to the current point (in the loop)
         iDirX2= x-iRandX1;
         iDirZ2= z-iRandZ1;
 
         //if the result of ( iDirX2*iDirZ1 - iDirX1*iDirZ2 ) is "up" (above 0),
         //then raise this point by iHeight
         if( ( iDirX2*iDirZ1 - iDirX1*iDirZ2 )> )
           fTempBuffer[( z*m_iSize )+x]+= ( float )iHeight;
       }
     }
     //erode terrain
     FilterHeightField( fTempBuffer, fFilter );
   }
   .......
   ..............
   return true;
 }

===================

代码的核心内容就是实现一个fault formation算法，算法是一个简单的数学模型，所以只要按照在纸上画个图就明白了。随笔的重点只是一行代码：

iDirX2*iDirZ1 - iDirX1*iDirZ2>0

这行代码参考的是二维向量共线定理：若设a=（x1，y1），b=（x2，y2），则有x1y2=x2y1。即与平行概念相同x1y2 - x2y1=0

另外，iMinDelta和iMaxDelta确实不符合我们的习惯，我们一般都习惯iMinValue和iMaxValue这样