Custom Postprocessing Effect

Now that both Postprocessing and the LWRP are out of preview, I'd like to find a way to recreate an effect I was able to do using the builtin renderer. Namely, setting the camera to 'Don't Clear' and a simple particle system I was able to create this:




I really like the aesthetic, and would like to use the new VFX graph but they have removed stacked cameras and the Don't clear option for cameras. I have read the Writing Custom Effects tutorial and it was quite easy to get a BW effect using a C# script and the shader provided. However, I am not good at shader writing at all, and I am not sure tool-wise how to approach what I think needs to happen to recreate this effect. A shader and shadergraph? Simply inserting a semi-transparent texture during Render() or another pass?

Can anyone help guide me in the right direction for creating a post effect that leaves a ghost trail like what I have working above? I would like it to be compatible with both the HDRP and LWRP, and it seems as if post processing effects would make this possible.

Conceptually, I know what needs to happen:

• Capture the last screen render (Blit is what I think I need)
• Set the alpha of the current screen capture to something less than opaque
• Render the current screen on top of the last screen (alpha or stencil seems like it would be useful)

Since each screen will include an semi-transparent pass of the last screen, it should create a ghost trail effect like the old Don't clear could do. For the above image, I placed a semitransparent quad in the view, which is how the effect seems to fade out.

I'd really like this to be as performant as possible, so that I can increase the particles and use real-time input like a camera feed to generate particles. So, I'm looking for advice on the most performant way to proceed.

Is this something that should be processed by a shader? Or, can a Blit function that copies the last screen work as well? Any help would be appreciated, I honestly don't know where to begin!

 

is a image effects of particle system?

 

The result of such process is just fantastic !! Looks like watercolor or sumi ink.... It is a shame that no support from Unity at all....... I am as well looking for a decent way to learn how to customize the PPS...