Ping pong buffer in postprocessing pass

[frmr]

I’m trying to set up a full screen quad with a ping pong buffer mouse trail. My camera position is tied to scroll and I originally set this up with a plane parented to the camera and used render targets using the camera, but when I scroll, the camera position offsets the mouse trail. So I’m thinking a post processing pass would be the better way to set this up, but I’m having trouble getting the ping pong buffer to work in a post processing pass while using the previous pass input with the ping pong buffer render targets. Am I thinking about this wrong? Are there any examples of this?