Visual indication or Effect to show when an object is occluded

Hey everyone. I’m building a program where you control a small avatar (this is a basic circle geometry or plane) that traverses through a scene filled with 3D Models and shapes. I’d like to achieve an effect similar to those found in many video games where you can see some sort of indication that the avatar is behind the various models and shapes. For example, here is an image to explain what i mean:

It doesn’t necessarily need to be the outline of the shape like in the image. I’m open to any effect really that shows some sort of indication that the avatar is behind something but also cant be too performance heavy as I’d like to get this program running on mobile. Being able to customise the effect somewhat (e.g. color, thickness, etc) is also highly desirable. Any advice or suggestions would be greatly appreciated. There really doesn’t seem to be much information that I can find to achieve an effect like this.

Also I thought it was worth mentioning that thus far I have attempted two things on my own. One is just rendering the avatar above everything. That turned out to look really silly and confusing. The other thing I attempted was to use an Outline post processing effect (from this library GitHub - vanruesc/postprocessing: A post processing library that provides the means to implement image filter effects for three.js.). Which actually looked pretty great but proved to be too performance heavy to run optimally at all times (not to mention other problems with color blending and transparent / see-through shapes and models)