Center rotationin of preveiw mesh and fix serialization of preview mesh

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/Graphs/AbstractMaterialGraph.cs

         [NonSerialized]
         List<Guid> m_RemovedProperties = new List<Guid>();
 
-        [NonSerialized]
+        [SerializeField]
         InspectorPreviewData m_PreviewData = new InspectorPreviewData();
 
         public InspectorPreviewData previewData
         }
     }
 
-
+    [Serializable]
-        public Mesh mesh;
+        public SerializableMesh serializedMesh = new SerializableMesh();
+
+        [NonSerialized]
+
+        [NonSerialized]
         public float scale = 1f;
     }
 }

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Inspector/GraphInspectorView.cs

             m_PreviewRenderHandle = previewManager.masterRenderData;
             m_PreviewRenderHandle.onPreviewChanged += OnPreviewChanged;
 
-            m_PreviewMeshPicker.SetValueAndNotify(m_Graph.previewData.mesh);
+            m_PreviewMeshPicker.SetValueAndNotify(m_Graph.previewData.serializedMesh.mesh);
 
             foreach (var property in m_Graph.properties)
                 m_PropertyItems.Add(new ShaderPropertyView(m_Graph, property));
 
             masterNode.onModified(masterNode, ModificationScope.Node);
 
-            if (m_Graph.previewData.mesh != changedMesh)
+            if (m_Graph.previewData.serializedMesh.mesh != changedMesh)
-            m_Graph.previewData.mesh = changedMesh;
+            m_Graph.previewData.serializedMesh.mesh = changedMesh;
         }
 
         public void UpdateSelection(IEnumerable<INode> nodes)

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/PreviewManager.cs

                 RenderTexture.active = renderData.renderTexture;
                 GL.Clear(true, true, Color.black);
                 Graphics.Blit(Texture2D.whiteTexture, renderData.renderTexture, m_SceneResources.checkerboardMaterial);
-                var mesh = (renderData == masterRenderData && m_Graph.previewData.mesh) ? m_Graph.previewData.mesh :  m_SceneResources.sphere;
+                var mesh = (renderData == masterRenderData && m_Graph.previewData.serializedMesh.mesh) ? m_Graph.previewData.serializedMesh.mesh :  m_SceneResources.sphere;
-                Graphics.DrawMesh(mesh, Matrix4x4.TRS(-mesh.bounds.center, rotation, Vector3.one * scale), m_PreviewMaterial, 1, m_SceneResources.camera, 0, m_PreviewPropertyBlock, ShadowCastingMode.Off, false, null, false);
+                Matrix4x4 previewTransform = Matrix4x4.identity;
+
+                if (renderData == masterRenderData)
+                {
+                    previewTransform *= Matrix4x4.Rotate(rotation);
+                    previewTransform *= Matrix4x4.Scale(Vector3.one * scale * .75f / mesh.bounds.extents.magnitude);
+                    previewTransform *= Matrix4x4.Translate(-mesh.bounds.center);
+                }
+
+                Graphics.DrawMesh(mesh, previewTransform, m_PreviewMaterial, 1, m_SceneResources.camera, 0, m_PreviewPropertyBlock, ShadowCastingMode.Off, false, null, false);
+
                 var previousUseSRP = Unsupported.useScriptableRenderPipeline;
                 Unsupported.useScriptableRenderPipeline = renderData.shaderData.node is IMasterNode;
                 m_SceneResources.camera.Render();