Masked postprocess

Unity Engine
1

Hey guys,
I have something to solve and I really dont know whats the correct way.
I have to apply an effect only to a specific kind of object. In this case, SSSSS for characters. But doesnt matter. To make the problem simple lets say I need a black and white texture to mask whats a character and the rest of the world. To illustrate this, I photoshoped the third image. Thats what I need to compose the final image:

1397211--72298--$Untitled-1.jpg
1397211--72298--$Untitled-1.jpg903×693 99.8 KB

In case its useful, the pipeline is as follows:

  1. Full Screen Postprocess
  2. Character rendered off-screen with Camera.RenderWithShader. Step 1 result is used here
  3. Compose original scene with step2 result using mask

This is for a paid project, so in case somebody has a good solution, we can talk about rewards.

Any idea? Thanks.

2

Its easy to mask any object(s) but this is not the correct way. It will look fake after composing.
Also, SSS should be applied per object shader and then finally do whatever screen post processing you have.
Anyways, if you still want it, pm me with details.

3

We can forget if this is SSS, SSSSS or whatever effect. The thing is that I need to compose the original scene with the Camera.RenderWithShader ones.
How? I dont know.
I used scene alpha first, but this is an adhoc solution. If we suppose every object in scene has alpha 1 and my character has alpha 0, then it will work. But once there is a 0 value alpha in the scene, then we have a problem.

4

1- Render scene with your object(s) only with desired alpha(White color) and the rest of the scene with black color(no alpha)
2- Render the rest of the scene as usual.
3- Render your object(s) alone as usual.
3- Compose 2 and 3 with the image in 1.

5

Sounds clever.
Does step 1 require ShaderReplacement? And in this case, (I dont know too much about unity) Does it require to render the whole world again? Meaning original drawcalls x 2

Thanks for your time!