[11.x] URP Shadergraph Fog Node should return fog intensity as density output

[Looooong]

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Purpose of this PR

Why is this PR needed, what hard problem is it solving/fixing?

In the URP, the Fog Node in Shadergraph outputs density using the result of ComputeFogFactor(z). However, the fog factor cannot be used mix fog color with fragment color. Instead, it must be passed to ComputeFogIntensity(fogFactor) to compute fog intensity, then this value is used to mix fog color with fragment color (this is how MixFogColor(fragColor, fogColor, fogFactor) is implemented). Therefore, instead of using fog factor, I suppose that Fog Node in Shadergraph should return fog intensity as density output. This will allow developer/designer to mix fog color using Lerp Node.

Testing status

Manual Tests

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Automated Tests

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Links

Yamato: (Select your branch) https://yamato.prd.cds.internal.unity3d.com/jobs/902-Graphics

Any test projects or documents to go with this to help reviewers?

Comments to reviewers

Notes for the reviewers you have assigned.

[eh-unity]

Sorry for taking a long time to review.
I had to look into fog code and see how it was done for all the other shaders. I did compare the graph node to URP Unlit and the change appears to be correct. It makes the fog node in shadergraph more consistent with the URP shaders. Still not perfect in every case, but that might be a second bug somewhere else (possibly the Unlit shader).

However, it changes the existing look and also flips the correct input parameter order for the lerp mixing the fog with material color.
Please add a descriptive change log entry, so users know what has changed and how to fix, if this affects their projects.

[Looooong]

I have added a changelog entry.

[phi-lira]

Adding @alindmanUnity as this is for shader graph.

[alindmanUnity]

just an update, because this changes the output from previous behavior we need to have an upgrade path for this node, as well as upgrade documentation, before we can accept the change. Shader Graph team is stretched a little thin, so this might take a while to be addressed unless the fix is raised as high priority.

[alindmanUnity]

We need to add an upgrade path for this change in behavior before it can be merged.

[phi-lira]

Closing due to inactivity. If you are still working on it, please reopen PR again.