[Fogbugz # 1398085] Fixing flicker when toggling hardware DRS (#6868)

* Fixing hardware drs one frame flicker

* Changelog

Co-authored-by: sebastienlagarde <[email protected]>

Author: kecho

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

@@ -77,6 +77,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed warning when an APV baking set is renamed.
 - Fixed issue where scene list was not refreshed upon deleting an APV baking set.
 - Fixed a null ref exception in Volume Explorer
+- Fixed one frame flicker on hardware DRS - (case 1398085)
 
 ## [14.0.0] - 2021-11-17
 

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

@@ -1300,16 +1300,26 @@ protected override void Render(ScriptableRenderContext renderContext, Camera[] c
                     HDAdditionalCameraData hdCam = null;
                     var drsSettings = m_Asset.currentPlatformRenderPipelineSettings.dynamicResolutionSettings;
 
+                    #region DRS Setup
+                    ////////////////////////////////
+                    // setup of DRS in the camera //
+                    ////////////////////////////////
+                    // First step we tell the DRS handler that we will be using the scaler set by the user. Note DLSS can set a system slot in case it wants to provide
+                    // the scale.
                     DynamicResolutionHandler.SetActiveDynamicScalerSlot(DynamicResScalerSlot.User);
                     if (camera.TryGetComponent<HDAdditionalCameraData>(out hdCam))
                     {
                         cameraRequestedDynamicRes = hdCam.allowDynamicResolution && camera.cameraType == CameraType.Game;
                     }
 
+                    // We now setup DLSS if its enabled. DLSS can override the drsSettings (i.e. setting a System scaler slot, and providing quality settings).
                     SetupDLSSForCameraDataAndDynamicResHandler(hdCam, camera, xrPass, cameraRequestedDynamicRes, ref drsSettings);
-                    DynamicResolutionHandler.UpdateAndUseCamera(camera, drsSettings);
 
+                    // only select the current instance for this camera. We dont pass the settings set to prevent an update.
+                    // This will set a new instance in DynamicResolutionHandler.instance that is specific to this camera.
+                    DynamicResolutionHandler.UpdateAndUseCamera(camera);
                     var dynResHandler = DynamicResolutionHandler.instance;
+
                     if (hdCam != null)
                     {
                         // We are in a case where the platform does not support hw dynamic resolution, so we force the software fallback.
@@ -1321,11 +1331,16 @@ protected override void Render(ScriptableRenderContext renderContext, Camera[] c
                         }
                     }
 
+                    // Notify the hanlder if this camera requests DRS.
                     dynResHandler.SetCurrentCameraRequest(cameraRequestedDynamicRes);
                     dynResHandler.runUpscalerFilterOnFullResolution = (hdCam != null && hdCam.cameraCanRenderDLSS) || DynamicResolutionHandler.instance.filter == DynamicResUpscaleFilter.TAAU;
 
+                    // Finally, our configuration is prepared. Push it to the drs handler
+                    dynResHandler.Update(drsSettings);
+
                     RTHandles.SetHardwareDynamicResolutionState(dynResHandler.HardwareDynamicResIsEnabled());
 
+                    #endregion
                     // Reset pooled variables
                     cameraSettings.Clear();
                     cameraPositionSettings.Clear();