can't you just use a sprite to overlay the los? seems like simplest solution to me
The behavior of LOS can interact with solid objects, that is, if there is a wall in front of it, then it will not see what is behind it.
If we just use the sprite, in this case it will pass through the wall without noticing it, the effect will not turn out.
It would be possible to use light with inversion, but unfortunately it works only for 1 light. if many sources the effect is lost.
It is not clear why they didn’t add to the LOS behavior just a color fill ... (