This function returns the union of two or more specified sets. 此函數返回兩個或更多指定集的並集。
These include functions to move, shrink and inflate rects, find the union of two rects, and a variety of collision-detection functions. 它們包括移動,收縮和膨脹矩形,找出兩個矩形的並集,和一堆的碰撞檢測函數。