/* 参考 ：http://www.cnblogs.com/wantnon/p/4947067.html
* http://fab.cba.mit.edu/classes/S62.12/docs/Meijster_distance.pdf
* 具体算法名：Saito算法
* 因为初始化值都是未知的，通过一个大约估计的初始化，来重复来回算一个大致准确的距离
* 值 ？
*/
public void generateDistanceField(OpenHeightfield field)
{
if (field == null)
{
Logger.LogError("[OpenHeightfieldBuilder][generateNeighborLinks]field Empty");
return;
}
/*
* 先将OpenHeightField的Span数据转换成0和1的二值图。如果是边缘Span
* 那么就是0，否则就是NEEDS_INIT。
*/
OpenHeightfield.OpenHeightFieldIterator iter = field.GetEnumerator();
while( iter.MoveNext() )
{
OpenHeightSpan span = iter.Current;
bool isBorder = false;
for(int dir = 0; dir < 4; ++dir)
{
OpenHeightSpan nSpan = span.getNeighbor(dir);
if( null == nSpan
|| nSpan.getNeighbor(dir == 3 ? 0 : dir + 1) == null)
{
//如果8个邻居有任何一个缺失的话，那么就是边界Border
isBorder = true;
break;
}
}
if( isBorder )
{
//自己就是边界Border
span.setDistanceToBorder(BORDER);
}
else
{
//需要再次计算
span.setDistanceToBorder(NEEDS_INIT);
}
} //while
/*
* 逆时针访问？
*
* (-1,1) (0,1) (1,1)
* (-1,0) x (1,0)
* (-1,-1) (0,-1) (1,-1)
*/
//Pass 1
//顺序访问 (-1,0) (-1,-1) (0,-1) (1,-1)
iter.Reset();
while( iter.MoveNext() )
{
OpenHeightSpan span = iter.Current;
int selfDist = span.distanceToBorder();
if( selfDist == BORDER)
{
continue;
}
//(-1,0)
OpenHeightSpan nSpan = span.getNeighbor(0);
selfDist = calcMiniDistanceToBorder(selfDist, nSpan, true);
//(-1,-1),左下角的领域
nSpan = nSpan.getNeighbor(3); //领域0的领域3，也就是原Span的左下角
selfDist = calcMiniDistanceToBorder(selfDist, nSpan, false);
//(0,-1)
nSpan = span.getNeighbor(3);
selfDist = calcMiniDistanceToBorder(selfDist, nSpan, true);
//(1,-1)
nSpan = nSpan.getNeighbor(2);
selfDist = calcMiniDistanceToBorder(selfDist, nSpan, true);
span.setDistanceToBorder(selfDist);
} // while
//Pass 2
//顺序访问 (1,0) (1,1) (0,1) (-1,1)
//注意这个是反向遍历
iter.ReverseReset();
while( iter.MoveNext() )
{
OpenHeightSpan span = iter.Current;
int selfDist = span.distanceToBorder();
if( selfDist == BORDER )
{
continue;
}
/*
* 因为经过Pass1之后 ，所有的Span要么就是Border
* 要么就是有个大概值的，不会等于NEED_INIT的。
* 所以直接按照按照上面的流程跑
*/
//(1,0)
OpenHeightSpan nSpan = span.getNeighbor(2);
selfDist = calcMiniDistanceToBorder(selfDist, nSpan, true);
//(1,1)
nSpan = nSpan.getNeighbor(1);
selfDist = calcMiniDistanceToBorder(selfDist, nSpan, false);
//(0,1)
nSpan = span.getNeighbor(1);
selfDist = calcMiniDistanceToBorder(selfDist, nSpan, true);
//(-1,1)
nSpan = nSpan.getNeighbor(0);
selfDist = calcMiniDistanceToBorder(selfDist, nSpan, false);
span.setDistanceToBorder(selfDist);
}
field.clearBorderDistanceBounds();
}
