[Port] [6000.0] UUM-78573: "Bake Probe Volumes" button does not store that lights are baked

https://jira.unity3d.com/browse/UUM-78573

This fix addresses a bug that caused the various buttons for baking only Adaptive Probe Volumes to malfunction - they would update the lights in the scene to act as baked, to avoid double-contribution from realtime lighting, but would do so in a way that wasn't persistent across scene reloads. 

The root cause is not properly respecting the Lighting Data Asset (LDA). The baked state of each light is stored in the LDA, _not_ on the lights themselves. Changing only the state on the lights themselves will not make a persistent change, and reloading the scene will reload the old unmodified data. To make the change persistent, we need to modify the LDA.

To fix this, I've taken an approach similar to what we do with reflection probes, which have the same issue:
- When you bake only probe volumes, and the scene has no LDA, we create a new empty LDA, assign it to the scene, and fill in the up-to-date states.
- When you bake only probes volumes, and the scene already has a LDA, we modify this LDA to contain up-to-date states for each light.

I had to add a few pieces of public API to achieve this.

Author: svc-reach-platform-support

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeGIBaking.LightTransport.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Runtime.CompilerServices;
 using Unity.Collections;
 using UnityEditor;
@@ -8,7 +9,7 @@
 using UnityEngine.LightTransport.PostProcessing;
 using UnityEngine.Rendering.Sampling;
 using UnityEngine.Rendering.UnifiedRayTracing;
-
+using UnityEngine.SceneManagement;
 using TouchupVolumeWithBoundsList = System.Collections.Generic.List<(UnityEngine.Rendering.ProbeReferenceVolume.Volume obb, UnityEngine.Bounds aabb, UnityEngine.Rendering.ProbeAdjustmentVolume volume)>;
 
 namespace UnityEngine.Rendering
@@ -584,13 +585,16 @@ public void Dispose()
             }
         }
 
+        // The contribution from all Baked and Mixed lights in the scene should be disabled to avoid double contribution.
         static void UpdateLightStatus()
         {
             var lightingSettings = ProbeVolumeLightingTab.GetLightingSettings();
 
-            // The contribution from all Baked and Mixed lights in the scene should be disabled to avoid double contribution.
-            var lights = Object.FindObjectsByType<Light>(FindObjectsSortMode.None);
-            foreach (var light in lights)
+            var sceneLights = new Dictionary<Scene, List<Light>>();
+
+            // Modify each baked light, take note of which scenes they belong to.
+            var allLights = Object.FindObjectsByType<Light>(FindObjectsSortMode.None);
+            foreach (var light in allLights)
             {
                 if (light.lightmapBakeType != LightmapBakeType.Realtime)
                 {
@@ -600,6 +604,56 @@ static void UpdateLightStatus()
                     bakingOutput.mixedLightingMode = lightingSettings.mixedBakeMode;
                     light.bakingOutput = bakingOutput;
                 }
+
+                // Take note of the lights from each scene
+                var scene = light.gameObject.scene;
+                if (!sceneLights.TryGetValue(scene, out var sceneLightList))
+                {
+                    sceneLightList = new List<Light>();
+                    sceneLights.Add(scene, sceneLightList);
+                }
+                sceneLightList.Add(light);
+            }
+
+            // Now we make the modifications persistent by modifying Lighting Data Assets (LDA) on disk.
+            string ldaFolderPath = Path.GetDirectoryName(AssetDatabase.GetAssetPath(m_BakingSet));
+            for (int i = 0; i < m_BakingSet.sceneGUIDs.Count; i++)
+            {
+                string guid = m_BakingSet.sceneGUIDs[i];
+                Scene scene = SceneManager.GetSceneByPath(AssetDatabase.GUIDToAssetPath(guid));
+                if (!scene.isLoaded)
+                    continue;
+
+                LightingDataAsset prevLDA = Lightmapping.GetLightingDataAssetForScene(scene);
+                LightingDataAsset newLDA = prevLDA;
+
+                // If the scene has no (modifiable) LDA, create a new one.
+                bool isDefaultLDA = prevLDA && prevLDA.hideFlags.HasFlag(HideFlags.NotEditable);
+                if (prevLDA == null || isDefaultLDA)
+                {
+                    newLDA = new LightingDataAsset(scene);
+                }
+
+                // Update the LDA with the new light settings
+                if (sceneLights.TryGetValue(scene, out var lights))
+                    newLDA.SetLights(lights.ToArray());
+                else
+                    newLDA.SetLights(Array.Empty<Light>());
+
+                // If the scene was using the builtin/default LDA before, copy over environment lighting, so it doesn't change.
+                if (prevLDA != null)
+                {
+                    newLDA.SetAmbientProbe(prevLDA.GetAmbientProbe());
+                    newLDA.SetDefaultReflectionCubemap(prevLDA.GetDefaultReflectionCubemap());
+                }
+
+                // Save the LDA to disk and assign it to the scene.
+                if (newLDA != prevLDA)
+                {
+                    string ldaPath = $"{ldaFolderPath}/LightingData-{i}.asset".Replace('\\', '/');
+                    AssetDatabase.CreateAsset(newLDA, ldaPath);
+                    Lightmapping.SetLightingDataAssetForScene(scene, newLDA);
+                }
             }
         }
 

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeGIBaking.cs

@@ -1234,7 +1234,7 @@ static void FixSeams(NativeArray<int> positionRemap, NativeArray<Vector3> positi
             // the dilation process consits in doing a trilinear sample of the higher subdivision brick and override the lower subdiv with that
             // We have to mark the probes on the boundary as valid otherwise leak reduction at runtime will interfere with this method
 
-            
+
             // Use an indirection structure to ensure mem usage stays reasonable
             VoxelToBrickCache cache = new VoxelToBrickCache();
 

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeVolumeLightingTab.cs

@@ -2,6 +2,7 @@
 using System.Linq;
 using System.Reflection;
 using System.Collections.Generic;
+using System.IO;
 using UnityEditor;
 using UnityEditor.Rendering;
 using UnityEditor.SceneManagement;
@@ -510,7 +511,9 @@ void SaveTempBakingSetIfNeeded()
             string path = string.IsNullOrEmpty(scene.path) ?
                 ProbeVolumeBakingSet.GetDirectory("Assets/", "Untitled") :
                 ProbeVolumeBakingSet.GetDirectory(scene.path, scene.name);
-            path = System.IO.Path.Combine(path, activeSet.name + ".asset");
+            if (!Directory.Exists(path))
+                Directory.CreateDirectory(path);
+            path = Path.Combine(path, activeSet.name + ".asset");
             path = AssetDatabase.GenerateUniqueAssetPath(path);
 
             AssetDatabase.CreateAsset(activeSet, path);