How to get screen-space bounding rect of the visible part of an actor?

Hi there.
My question is simple.
There is an actor. Assuming its in front of the camera. So it can be visible, or partially visible, or hidden behind the others actors.
How i can get screen-space bounding rect of visible pixels of this actor? This rect can be from previous frame, its ok.

The simpliest way to get it, as for me, is projecting actor’s bounding box to the screen, get screen rect of it, and then create ray for each pixel. Use LineTraces to determine if ray hits with my actor. Single LineTrace is not for each screen pixel, but for block 12x12 pixels, for example. After this compose bounding rect from this array of hits.

This is ok, but i think its some brute. And im afraid this can be expensive in some cases. Maybe you can help me and tell how to do this in better way?
Thanks for all.