How to get Initial texture in Post-Processing Stack v2


I’m trying to write a custom post-processing shader with new Post-Processing Stack v2.
I already have a few effects in my pipeline, but I need to determine whether I apply them or not based on condition.

So, I need to obtain the initial source texture right from camera, before all effects were applied and return it’s value if I need.

The logic is to have the mask layer, camera that renders this layer into a texture and post-effect for masking.

Thanks a lot.

Anybody? Please.