Added shadowmask and shadowmask distance support

[lukaschod]

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• Have you added a graphic test for your PR (if needed)? When you add a new feature, or discover a bug that tests don't cover, please add a graphic test.

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Purpose of this PR

• Added shadowmask and shadowmask distance support.
• Renaming _MIXED_LIGHTING_SUBTRACTIVE into LIGHTMAP_SHADOW_MIXING. This gives us few advantages: consistency with builtin/hdrp, re-using existing builtin keyword, keyword stripping is automatically handled by core, we use keyword of core functionality.
• Refactoring lightOcclusionChannel to work as lightShadowMaskSelector (Where we used mask). Sadly I can not renamed property as it would break public API.
• Refactoring unity_ProbesOcclusion to be applied in MixRealtimeAndBakedShadows instead of light.distanceAttenuation. This way keeping similar functionality to builtin. Now light probes behaves more closely what we have in builtin.
• Changing shadow fade to be calcualte inside MixRealtimeAndBakedShadows instead of in Light gathering. As this way required by realtime and baked shadow mixing.

For more information please check the card https://jira.unity3d.com/browse/URP-36!

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Testing status

Manual Tests: What did you do?

• Opened test project + Run graphic tests locally
• Built a player
• Checked new UI names with UX convention
• Tested UI multi-edition + Undo/Redo + Prefab overrides + Alignment in Preset
• C# and shader warnings (supress shader cache to see them)
• Checked new resources path for the reloader (in developer mode, you have a button at end of resources that check the paths)
• Other:

Comparing URP and Builtin mixed lighting. Simple scene with static walls, dynamic cube and lightprobes group.:

Builtin Mixed Lighting Subtractive + Probes

• Static mesh keywords LIGHTMAP_ON LIGHTMAP_SHADOW_MIXING.
• Static mesh effected by LIGHMAP + SCREENSPACE_SHADOWS.
• Dynamic mesh keywords LIGHTMAP_SHADOW_MIXING.
• Dynamic mesh effected by PROBES + SCREENSPACE_SHADOWS.
  
  URP Mixed Lighting Subtractive + Probes
  

Builtin Mixed Lighting ShadowMask + Probes

• Static mesh keywords LIGHTMAP_ON LIGHTMAP_SHADOW_MIXING SHADOWS_SHADOWMASK.
• Static mesh effected by SHADOWMASK + SCREENSPACE_SHADOWS.
• Dynamic mesh keywords LIGHTMAP_SHADOW_MIXING.
• Dynamic mesh effected by PROBES + SCREENSPACE_SHADOWS.
  
  URP Mixed Lighting ShadowMask + Probes
  

Builtin Mixed Lighting ShadowMask + Distance + Probes

• Static mesh keywords LIGHTMAP_ON SHADOWS_SHADOWMASK.
• Static mesh effected by SHADOWMASK + SCREENSPACE_SHADOWS.
• Dynamic mesh keywords None.
• Dynamic mesh effected by PROBES + SCREENSPACE_SHADOWS. (Probes turn only when realtime is out of distance)
  
  URP Mixed Lighting ShadowMask + Probes (Has harder cut-off, but it is not part of shadowmask change. However it is something we should look into.)
  

Automated Tests:
049_Lighting_Mixed_Subtractive

043_Lighting_Mixed_ShadowMask

134_Lighting_Mixed_ShadowMask_Distance

Yamato:
https://yamato.prd.cds.internal.unity3d.com/jobs/902-Graphics/tree/universal%252Fshadow-mask-support

Any test projects to go with this to help reviewers?

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For QA

• Check if mixed lighting subtractive did not regressed in any way.
• Check if mised lighting shadowmask and shadowmask distance works similar to builtin.
• Make sure keywords are stripped if mixed lighting is not used (Either disabled in pipeline asset or not enabled in lighting settings or not baked).

[w1shmast3r]

QA pass has revealed the following issue: No baked shadowmask is rendered after switching the shadowmask mode to Distance shadowmask, rebaking and setting shadow distance to 0.
For more details regarding the repro (project, steps, repro video, and images) please refer to the following link.
This bug needs to be fixed prior to merging this PR.

[lukaschod]

QA pass has revealed the following issue: No baked shadowmask is rendered after switching the shadowmask mode to Distance shadowmask, rebaking and setting shadow distance to 0.
For more details regarding the repro (project, steps, repro video, and images) please refer to the following link.
This bug needs to be fixed prior to merging this PR.

Fixed in latest commit

[w1shmast3r]

Added @Unity-Technologies/mobile-qa for test pass on mobiles and Linux. More information regarding platform testing could be found here: https://docs.google.com/spreadsheets/d/1OAmFn25Y4OyhQqGeZF-ZSPQPzhfWK_ZXw9-6MmgwtU8/edit#gid=868713657

[ghost]

Automated test 049_Lighting_Mixed_Subtractive seems to fail right out of the gate when run manually on this branch... any idea why?

[ghost]

Switched the PBR materials in the automated tests to shadergraph materials and ensured that the results were still identical visually after baking.

[phi-lira]

What's status on this PR?

[vaidasma]

finishing manual shadowmask testing today

[w1shmast3r]

Still waiting for the clarification for this recently found bug: https://confluence.unity3d.com/display/teamgi/%5BURP%5D+-+Shadowmask+Support#id-[URP]-ShadowmaskSupport-bug7 other than that the Lighting QA test pass is done.

[w1shmast3r]

Lighting QA test pass has been completed on Windows and macOS (both using Editor and Standalone Player.
Link to the feature test doc: https://confluence.unity3d.com/display/teamgi/%5BURP%5D+-+Shadowmask+Support

Tested with using Unity Version 2020.2.0b3 (ef376aff2859)
Branch: trunk

Tested on the following projects:

• URP Sample scene
• CornellBox URP;
• Sponza URP.

Testing included:

• Checking that the shadowmask gets generated for all aforementioned projects;
• Testing both Shadowmask and Distance Shadowmask modes and ensuring that the behaviour is consistent with the built-in RP;
• Testing some complicated scenarios with baked shadowmask (overlapping lights, toggling shadow distance, switching between lighting modes at runtime, etc)
• Integration with different lightmap backends (CPU/GPU PLM, Enlighten), different shaders and geometry (terrains).

Test outcomes:

• Several UI and functional bugs found, addressed and verified;
• 1 known UI issue: No Light Overlap mode scene view visualization filter in URP. Discussed that with Lukas and decided that due to the complexity of the potential fix, we need to fix this bug separately.
• Several unrelated issues related to URP integration with certain shaders and mixed lighting modes found. All of them have been logged to FogBugz;
• No other new regressions or ship-stoppers introduced by this PR have been found.

Approving as or revision 3f7f2fc. Great job!

[vaidasma]

Feature looks good on Android and iOS, no artifacts or unexpected behaviours detected. Testing document: https://docs.google.com/document/d/1pshQpUoKHpe7bMmiWVCYzPrUGt44o6whiFMycNDWHIY/edit?usp=sharing

Additional project were not covered in order not to bottleneck the feature time-wise. If additional coverage needed, please contact me.

[phi-lira]

Cancelled yamato. Previous commit was green and new one just fixed a conflict in editor build settings.