[Backport 2021.1] Fix history buffer allocation for AOVs when the request does not come in first frame (#4419)

* Fix  history buffer allocation for AOVs when the request does not come in first frame

# Conflicts:
#	com.unity.render-pipelines.high-definition/CHANGELOG.md
#	com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Camera/HDCamera.cs

Fix bad merge

* Changelog

Author: pmavridis

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -185,6 +185,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed contact shadows tile coordinates calculations.
 - Fixed blocky looking bloom when dynamic resolution scaling was used.
 - Fixed material Emission properties not begin animated when recording an animation (case 1328108).
+- Fixed issue with history buffer allocation for AOVs when the request does not come in first frame.
 
 ### Changed
 - Removed the material pass probe volumes evaluation mode.

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Camera/HDCamera.cs

@@ -684,10 +684,24 @@ internal void Update(FrameSettings currentFrameSettings, HDRenderPipeline hdrp,
                 if (isHistoryColorPyramidRequired) // Superset of case above
                     numColorPyramidBuffersRequired = 2;
 
-                int numVolumetricBuffersRequired = isVolumetricHistoryRequired ? 2 : 0; // History + feedback
+                bool forceReallocPyramid = false;
+                int colorBufferID = (int)HDCameraFrameHistoryType.ColorBufferMipChain;
+                int numColorPyramidBuffersAllocated = m_HistoryRTSystem.GetNumFramesAllocated(colorBufferID);
 
-                if ((m_NumColorPyramidBuffersAllocated != numColorPyramidBuffersRequired) ||
-                    (m_NumVolumetricBuffersAllocated != numVolumetricBuffersRequired))
+                // Check if we have any AOV requests that require history buffer allocations (the actual allocation happens later in this function)
+                foreach (var aovRequest in aovRequests)
+                {
+                    var aovHistory = GetHistoryRTHandleSystem(aovRequest);
+                    if (aovHistory.GetNumFramesAllocated(colorBufferID) != numColorPyramidBuffersRequired)
+                    {
+                        forceReallocPyramid = true;
+                        break;
+                    }
+                }
+
+                int numVolumetricBuffersRequired = isVolumetricHistoryRequired ? 2 : 0; // History + feedback
+                if ((numColorPyramidBuffersAllocated != numColorPyramidBuffersRequired) ||
+                    (m_NumVolumetricBuffersAllocated != numVolumetricBuffersRequired) || forceReallocPyramid)
                 {
                     // Reinit the system.
                     colorPyramidHistoryIsValid = false;
@@ -723,7 +737,6 @@ internal void Update(FrameSettings currentFrameSettings, HDRenderPipeline hdrp,
                     }
 
                     // Mark as init.
-                    m_NumColorPyramidBuffersAllocated = numColorPyramidBuffersRequired;
                     m_NumVolumetricBuffersAllocated   = numVolumetricBuffersRequired;
                 }
             }
@@ -1136,7 +1149,6 @@ public RTHandle Allocator(string id, int frameIndex, RTHandleSystem rtHandleSyst
 
         HDAdditionalCameraData  m_AdditionalCameraData = null; // Init in Update
         BufferedRTHandleSystem  m_HistoryRTSystem = new BufferedRTHandleSystem();
-        int                     m_NumColorPyramidBuffersAllocated = 0;
         int                     m_NumVolumetricBuffersAllocated   = 0;
         float                   m_AmbientOcclusionResolutionScale = 0.0f; // Factor used to track if history should be reallocated for Ambient Occlusion
         float                   m_ScreenSpaceAccumulationResolutionScale = 0.0f; // Use another scale if AO & SSR don't have the same resolution