Light bleeding happens in umbra area where the mipmap layers are filtered right away, so that the inconsistent filter sizes break the accumulation  law of of blocked light in the filter areas – not all the blocked light are added to 1.

But the things is, if we can prevent the fully-blocked fragment being filtered, we would fix light bleeding. Idea: check if the fragment is fully blocked in layers blocking any light. If all the layers block the fragment, don’t filter.

The idea theoretically works but when I implemented it, light bleeding doesn’t seem fixed :_(