Different Color Grading for different Render Layers.

[Kleptine]

This implements separate post processing for different layers of objects.

With the new SRP, all renderers now have a 'RenderingLayer'. This is a bitmask of potential render layers an object can be on, distinct from the normal "Layer" that a gameobject can exist on. This change makes use of this setting (otherwise unused in URP as far as I can tell) to do two things:

1. Split out the opaque DrawObjectsPass into multiple subpasses, one for each render layer.
2. Split the ColorGradingLUTPass into multiple passes, rendering a post processing LUT for each render layer.

Normally post processing Volumes apply to all rendered objects. This change also adds an additional setting on Volumes to specify which RenderingLayers they affect. The pipeline builds separate post processing stacks for each rendering layer with different post processing settings. These stacks are passed into step 2, and rendered into the LUT.

I'm not totally happy with the conciseness of this change. It's not actually all that complex, but it's fairly invasive, and I worry about conflicts. That said, I think this feature is really valuable, especially as we work towards getting to a clearer style.

Performance effects haven't yet been tested. This adds an extra LUT render for every rendering layer with separate post effects, which is small but an increase. Splitting the opaque pass should have limited affects, but affects sorting of drawcalls, which could create more overdraw.

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This change is 

[matteblair]

There's something weird with the post-processing volume in the main scene, it seems like it's got two of all the components that it's supposed to have from the post profile. This makes the settings behave unexpectedly. I was able to create a new volume using an existing post profile and then it worked as expected.

The only thing that doesn't seem to work is that changing the tonemapping mode seems to have no effect - I'm not sure whether it's being applied at all. If I checkout the current "master" for the submodule, I'm able to see a clear difference between tonemapping modes in the same scene, so its something to do with this change.

[Kleptine]

Hmm.. odd. Might be worth screen sharing tomorrow at standup. Tonemapping is definitely working for me, or at least last time I checked.

[Kleptine]

Oh, regarding the settings in the main scene. You'd need to be on my branch for that: john/per-object-postprocessing. That said, it shouldn't be broken -- I'm not entirely sure what you're observing.

[matteblair]

Yeah I can just show you tomorrow.

There's also the broader question of "is this a good tool for our renderer". I'm not totally sure. I don't think we should be leaning on post-processing to do a lot of heavy lifting for the visuals. The volume system has a somewhat limited set of knobs for us to turn - especially since we're limiting ourselves to only the operations that we can do in the forward pass. Instead, I think what might serve us better is to work more with customizing materials.

We could make a custom version (or several versions) of the URP Lit shader and add parameters for stylization there. In a shader we'd have much more control over the effects and their performance characteristics. Keeping our work in the materials would probably play a lot nicer with existing workflows too.

[Kleptine]

Yeah, I agree. The way I see it, we should be reaching for materials for the bulk of the work, and then for PostProcessing only for the tasks that can't be accomplished easily any other way.

I'm fairly hesitant to actually branch the URP Lit Shader. It would cause it to stop working with ShaderGraph's Lit Master node, and I think it would really start to be a maintenance headache. I'd much prefer to make small modifications to the core lit shader, with static branches, such as adding subsurface scattering.

You may also be underestimating the number of knobs in the Volume system. There's ~10 different components that all affect color grading, many of which I used in some of the tuning I did recently. The big benefit of using Volumes is that all of these knobs can be used for no performance cost -- they get baked into the LUT.

[Kleptine]

Ok, I've rebased this on top of the latest graphics repo. It's not all that bad, or at least no worse than any other graphics PR has been.

[SoumyaRipan]

Hi, Thank you so much for creating this. I have cloned this project for testing the custom postprocess effect in forward render of URP.
But after opening up the project in 2020.3.39f1, it shows all urp materials black.
Can you please tell, what can be the reason for this?

[Kleptine]

Hi, unfortunately this repository is provided for reference only! So there's no guarantees that it will work in a generic project, and has many optimizations in it that are specific to The Last Clockwinder.

That said, note the checkbox in the lit shader "Realtime Main Light". We disabled the main directional light in this branch because we don't use it.