The source object must not obscure the target, and because the source object is big enough to span multiple drop candidates, we need to use a cursor hotspot to precisely indicate which candidate it will be dropped on.

• 源对象不能模糊目标对象，因为源对象大到横跨多个拖放候选对象，我们需要用光标热点精确显示其将拖放到哪个拖放候选对象上。