Manager for Homogenous volumes.

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/HomogeneousDensityVolume.cs

 
         private void OnEnable()
         {
+            DensityVolumeManager.manager.RegisterVolume(this);
+            DensityVolumeManager.manager.DeRegisterVolume(this);
         }
 
         private void Update()

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/DensityVolumeManager.cs

+using System.Collections.Generic;
+
+namespace UnityEngine.Experimental.Rendering.HDPipeline
+{
+    public class DensityVolumeManager 
+    {
+        static private DensityVolumeManager _instance = null;
+        private DensityVolumeManager()
+        {
+            volumes = new List<HomogeneousDensityVolume>();
+        }
+
+        public static DensityVolumeManager manager
+        {
+            get 
+            {
+                if (_instance == null)
+                {
+                    _instance = new DensityVolumeManager();
+                }
+                return _instance;
+            }
+        }
+
+        private List<HomogeneousDensityVolume> volumes = null;
+
+        public void RegisterVolume(HomogeneousDensityVolume volume)
+        {
+            volumes.Add(volume);
+        }
+
+        public void DeRegisterVolume(HomogeneousDensityVolume volume)
+        {
+            if (volumes.Contains(volume))
+            {
+                volumes.Remove(volume);
+            }
+        }
+
+        public HomogeneousDensityVolume[] GetAllVolumes()
+        {
+            return volumes.ToArray();
+        }
+    }
+}

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/DensityVolumeManager.cs.meta

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