Don't check textures slots in decal material validation

Add gizmo for selecting decals in scene view
Add material fold out in the DecalProjectorComponent inspector

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Decal/DecalProjectorComponent.cs

             }
         }
 
+        public Material Mat
+        {
+            get { return this.m_Material; }
+        }
+
         public void OnEnable()
         {
             DecalSystem.instance.AddDecal(this);
             DecalSystem.instance.UpdateBoundingSphere(this);
         }
 
+        public void OnDrawGizmos()
+        {
+            DrawGizmo(false);
+        }
+
-
-            if (!m_Material.GetTexture("_BaseColorMap") && !m_Material.GetTexture("_NormalMap") &&
-                !m_Material.GetTexture("_MaskMap"))
-                return false;
-
             return true;
         }
     }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/Decal/DecalProjectorComponentEditor.cs

+using System;
+using UnityEngine;
+using UnityEngine.Experimental.Rendering;
+using UnityEngine.Experimental.Rendering.HDPipeline;
+using UnityEditor;
+
+namespace UnityEditor.Experimental.Rendering.HDPipeline
+{
+    [CustomEditor(typeof(DecalProjectorComponent))]
+    public class DecalProjectorComponentEditor : Editor
+    {
+        private MaterialEditor m_MaterialEditor = null;
+        private DecalProjectorComponent m_DecalProjectorComponent = null;
+
+        private void OnEnable()
+        {
+            // Create an instance of the MaterialEditor
+            m_DecalProjectorComponent = (DecalProjectorComponent)target;
+            m_MaterialEditor = (MaterialEditor)CreateEditor(m_DecalProjectorComponent.Mat);    
+        }
+
+        public override void OnInspectorGUI()
+        {
+            EditorGUI.BeginChangeCheck();
+
+            base.OnInspectorGUI();
+            if (EditorGUI.EndChangeCheck())
+            {
+                serializedObject.ApplyModifiedProperties();
+            }
+
+            if (m_MaterialEditor != null)
+            {
+                // Draw the material's foldout and the material shader field
+                // Required to call m_MaterialEditor.OnInspectorGUI ();
+                m_MaterialEditor.DrawHeader();
+
+                //  We need to prevent the user to edit Unity default materials
+                bool isDefaultMaterial = !AssetDatabase.GetAssetPath(m_DecalProjectorComponent.Mat).StartsWith("Assets");
+                using (new EditorGUI.DisabledGroupScope(isDefaultMaterial))
+                {
+                    // Draw the material properties
+                    // Works only if the foldout of m_MaterialEditor.DrawHeader () is open
+                    m_MaterialEditor.OnInspectorGUI();
+                }
+            }
+        }
+    }
+}