This concept is rather simple. It's pretty easy to create screen effects that will affect only screen behing a specific mesh.

For example let's create a simple scanner effect.

(Material domain should be set to Translucent)

TransparentPostprocess

Scanner-1

The main idea is to use the Scene Color node that returns the color behind your transparent object.

I multiply the Scene Color by a reddish color - multiplying color by a different color results with a tint effect.

I've also used Custom Depth buffer to be able to render a shilouette of geometry behind the wall. The If node does the following:

  • Check the value of the Custom Depth buffer.
  • If it's greater than zero it means that there is some object on the scene that renders CustomDepth Pass. So... Let's output blue.
  • If the value is less or equal to zero, there is nothing special. Let's output the Scene Color tinted red.

The Custom Depth buffer on my scene looks like this:
ScannerCustomDepth

Remember to enable Render CustomDepth Pass on the mesh you want to have visible!
CustomDepthPass-1