scanfill

代码说明：

  光栅图形学中的扫描填充算法。list AET和list* NET构成了活性边表和新边表.算法先初始化各扫描线新边表,之后对于每条扫描线更新活性边表，并且配对交点来着色。 (Raster graphics scanning fill algorithm. list AET list * NET constitute the active side of the table and side table new algorithm to initialize each scan line side table new, after each scan line update the active side of the table, and the the paired intersection of coloring.)