[HDRP] Adding information about SSGI and Emissive incompatibility in documentation and override

com.unity.render-pipelines.high-definition/Documentation~/Override-Screen-Space-GI.md

@@ -74,6 +74,12 @@ HDRP uses the [Volume](Volumes.md) framework to calculate SSGI, so to enable and
 
 ## Limitations
 
+In Deferred rendering mode, Screen Space Global Illumination and Ray-Traced Global Illumination share a buffer with emissive, which overwrites emissive data. 
+There are multiple ways to recover the emissive contribution of the scene materials: 
+* Disable [Receive SSR/SSGI](snippets/shader-properties/surface-options/receive-ssr.md) flag on the emissive materials.
+* Use [Force Forward Emissive](snippets/shader-properties/advanced-options/force-forward-emissive.md) on the emissive materials.
+* Use Forward rendering.
+
 ### Screen-space global illumination
 
 * When rendering [Reflection Probes](Reflection-Probe.md) screen space global illumination is not supported.

com.unity.render-pipelines.high-definition/Editor/RenderPipeline/Raytracing/GlobalIlluminationEditor.cs

@@ -173,7 +173,10 @@ public override void OnInspectorGUI()
             }
 
             PropertyField(m_Enable);
-
+			if (m_Enable.value.boolValue)
+				EditorGUILayout.HelpBox("Real-time Global Illumination overwrites emissive data in deferred rendering mode. To recover the emissive contribution, either use Force Forward Emissive or disable Receive SSR/SSGI flag on the emissive materials.", MessageType.Info);
+            EditorGUILayout.Space();
+
             // If ray tracing is supported display the content of the volume component
             if (HDRenderPipeline.buildPipelineSupportsRayTracing)
                 PropertyField(m_Tracing);