Add initial preview hiding (still being rendered behind the scenes)

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Presenters/MaterialGraphPresenter.cs

 
         public void RemoveElements(IEnumerable<MaterialNodePresenter> nodes, IEnumerable<GraphEdgePresenter> edges)
         {
-            graph.RemoveElements(nodes.Select(x => x.node), edges.Select(x => x.edge));
+            graph.RemoveElements(nodes.Select(x => x.node as INode), edges.Select(x => x.edge));
             graph.ValidateGraph();
         }
 
                 return;
 
             var addedNodes = new List<INode>();
-
             var nodeGuidMap = new Dictionary<Guid, Guid>();
             foreach (var node in copyGraph.GetNodes<INode>())
             {
 
             // only connect edges within pasted elements, discard
             // external edges.
-            var addedEdges = new List<IEdge>();
-
             foreach (var edge in copyGraph.edges)
             {
                 var outputSlot = edge.outputSlot;
                 {
                     var outputSlotRef = new SlotReference(remappedOutputNodeGuid, outputSlot.slotId);
                     var inputSlotRef = new SlotReference(remappedInputNodeGuid, inputSlot.slotId);
-                    addedEdges.Add(graph.Connect(outputSlotRef, inputSlotRef));
+                    graph.Connect(outputSlotRef, inputSlotRef);
-
-            //TODO: Fix this
-            //drawingData.selection = addedNodes.Select(n => n.guid);
+            if (onSelectionChanged != null)
+                onSelectionChanged(addedNodes);
         }
 
         public bool canCopy
             if (graph == null)
                 return;
             if (onSelectionChanged != null)
-                onSelectionChanged(presenters.Select(x => x.node));
+                onSelectionChanged(presenters.Select(x => x.node as INode));
         }
 
         public override void AddElement(GraphElementPresenter element)

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Presenters/MaterialNodePresenter.cs

     [Serializable]
     public class MaterialNodePresenter : NodePresenter, IDisposable
     {
-        public INode node { get; private set; }
+        public AbstractMaterialNode node { get; private set; }
 
         [SerializeField]
         protected List<GraphControlPresenter> m_Controls = new List<GraphControlPresenter>();
 
         public virtual void Initialize(INode inNode, PreviewSystem previewSystem)
         {
-            node = inNode;
+            node = inNode as AbstractMaterialNode;
 
             if (node == null)
                 return;

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Views/MaterialNodeView.cs

+using System;
 using System.Collections.Generic;
 using System.Linq;
 using UnityEditor.Experimental.UIElements.GraphView;
     {
         VisualElement m_ControlsContainer;
         List<GraphControlPresenter> m_CurrentControls;
-        VisualElement m_PreviewContainer;
+        VisualElement m_PreviewToggle;
         Image m_PreviewImage;
         bool m_IsScheduled;
 
             leftContainer.Add(m_ControlsContainer);
             m_CurrentControls = new List<GraphControlPresenter>();
 
-            m_PreviewContainer = new VisualElement { name = "preview" };
+            m_PreviewToggle = new VisualElement { name = "toggle", text = "" };
+            m_PreviewToggle.AddManipulator(new Clickable(OnPreviewToggle));
+            leftContainer.Add(m_PreviewToggle);
+
+            m_PreviewImage = new Image
-                m_PreviewImage = new Image
-                {
-                    pickingMode = PickingMode.Ignore,
-                    image = Texture2D.whiteTexture
-                };
-            }
-            leftContainer.Add(m_PreviewContainer);
+                name = "preview",
+                pickingMode = PickingMode.Ignore,
+                image = Texture2D.whiteTexture
+            };
+            leftContainer.Add(m_PreviewImage);
+        }
+
+        void OnPreviewToggle()
+        {
+            var node = GetPresenter<MaterialNodePresenter>().node;
+            node.previewExpanded = !node.previewExpanded;
+            m_PreviewToggle.text = node.previewExpanded ? "▲" : "▼";
         }
 
         void UpdatePreviewTexture(Texture previewTexture)
-                m_PreviewContainer.Clear();
+                m_PreviewImage.visible = false;
+                m_PreviewImage.RemoveFromClassList("visible");
+                m_PreviewImage.AddToClassList("hidden");
-                if (m_PreviewContainer.childCount == 0)
-                    m_PreviewContainer.Add(m_PreviewImage);
+                m_PreviewImage.visible = true;
+                m_PreviewImage.AddToClassList("visible");
+                m_PreviewImage.RemoveFromClassList("hidden");
-            Dirty(ChangeType.Repaint | ChangeType.Layout);
+            Dirty(ChangeType.Repaint);
+
         }
 
         void UpdateControls(MaterialNodePresenter nodeData)
             {
                 m_ControlsContainer.Clear();
                 m_CurrentControls.Clear();
-                m_PreviewContainer.Clear();
+
+            m_PreviewToggle.text = nodePresenter.node.previewExpanded ? "▲" : "▼";
+            if (nodePresenter.node.hasPreview)
+                m_PreviewToggle.RemoveFromClassList("inactive");
+            else
+                m_PreviewToggle.AddToClassList("inactive");
-//            if (nodePresenter.expanded)
-            UpdatePreviewTexture(nodePresenter.previewTexture);
-
-//            else
-//                m_PreviewContainer.Clear();
+            UpdatePreviewTexture(nodePresenter.node.previewExpanded ? nodePresenter.previewTexture : null);
         }
     }
 }

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Resources/Styles/MaterialGraph.uss

     width: 400;
 }
 
-MaterialNodeView > .mainContainer > #left > #preview > Image {
+MaterialNodeView > .mainContainer > #left > #preview.active {
+    width: 200;
+}
+
+MaterialNodeView > .mainContainer > #left > #preview.visible {
-	width: 200;
+}
+
+MaterialNodeView > .mainContainer > #left > #toggle {
+    text-color: rgb(153, 153, 153);
+    text-alignment: middle-center;
+}
+
+MaterialNodeView > .mainContainer > #left > #toggle.inactive {
+    height: 0;
+}
+
+MaterialNodeView > .mainContainer > #left > #toggle:hover {
+	background-color: rgba(0, 0, 0, 0.33);
+}
+
+MaterialNodeView > .mainContainer > #left > #toggle:active {
+	background-color: rgba(0, 0, 0, 0.66);
 }
 
 GridBackground {

MaterialGraphProject/Assets/UnityShaderEditor/Runtime/Nodes/AbstractMaterialNode.cs

 using System;
 using System.Collections.Generic;
 using System.Linq;
+using UnityEditor;
 using UnityEngine.Graphing;
 
 namespace UnityEngine.MaterialGraph
 
         //[SerializeField]
         private OutputPrecision m_OutputPrecision = OutputPrecision.@float;
+
+        [SerializeField]
+        bool m_PreviewExpanded;
+
+        public bool previewExpanded
+        {
+            get { return m_PreviewExpanded; }
+            set { m_PreviewExpanded = value; }
+        }
 
         // Nodes that want to have a preview area can override this and return true
         public virtual bool hasPreview