Invisiblity area

Hey guys,

So here is what im trying to do: a character moves in our out of an area and becomes invisible as long as he is in that area. I want to hide parts of the mesh AS they are going into the area, not the whole mesh at once. I have some ideas on how to go about this, but they all seem pretty complicated, i am sure there is an easy way about this. The method does not need to be perfect, if polygons only get hidden once all of its verts are inside the area, thats okay too.


If there are no ideas, how about having two translucent object obscure each other? Back in the day, it was not uncommon to only be able to show one translucent item, so a 100% translucent item would obscure a 50% translucent item completely, making it seems like it was also completely invisible.