Add drag and drop to graph for Texture2D and subgraphs

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

                 m_GraphView.AddManipulator(new SelectionDragger());
                 m_GraphView.AddManipulator(new ClickSelector());
                 m_GraphView.AddManipulator(new NodeCreator(graph));
+                m_GraphView.AddManipulator(new GraphDropTarget(graph));
                 content.Add(m_GraphView);
 
                 m_GraphInspectorView = new GraphInspectorView(asset.name, previewManager, graph) { name = "inspector" };

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Manipulators/GraphDropTarget.cs

+using System.Linq;
+using UnityEngine;
+using UnityEngine.Experimental.UIElements;
+using UnityEngine.MaterialGraph;
+
+namespace UnityEditor.MaterialGraph.Drawing
+{
+    public class GraphDropTarget : Manipulator
+    {
+        AbstractMaterialGraph m_Graph;
+        MaterialGraphView m_GraphView;
+
+        public GraphDropTarget(AbstractMaterialGraph graph)
+        {
+            m_Graph = graph;
+        }
+
+        protected override void RegisterCallbacksOnTarget()
+        {
+            m_GraphView = target as MaterialGraphView;
+            target.RegisterCallback<IMGUIEvent>(OnIMGUIEvent);
+        }
+
+        protected override void UnregisterCallbacksFromTarget()
+        {
+            target.UnregisterCallback<IMGUIEvent>(OnIMGUIEvent);
+        }
+
+        bool ValidateObject(Object obj)
+        {
+            return EditorUtility.IsPersistent(obj)
+                && (obj is Texture2D || obj is MaterialSubGraphAsset);
+        }
+
+        void CreateNode(Object obj, Vector2 nodePosition)
+        {
+            var texture2D = obj as Texture2D;
+            if (texture2D != null)
+            {
+                m_Graph.owner.RegisterCompleteObjectUndo("Drag Texture");
+                var property = new TextureShaderProperty { displayName = texture2D.name, value = { texture = texture2D } };
+                m_Graph.AddShaderProperty(property);
+                var node = new PropertyNode();
+                var drawState = node.drawState;
+                drawState.position = new Rect(nodePosition, drawState.position.size);
+                node.drawState = drawState;
+                m_Graph.AddNode(node);
+                node.propertyGuid = property.guid;
+            }
+
+            var subGraphAsset = obj as MaterialSubGraphAsset;
+            if (subGraphAsset != null)
+            {
+                var node = new SubGraphNode();
+                var drawState = node.drawState;
+                drawState.position = new Rect(nodePosition, drawState.position.size);
+                node.drawState = drawState;
+                node.subGraphAsset = subGraphAsset;
+                m_Graph.AddNode(node);
+            }
+        }
+
+        void OnIMGUIEvent(IMGUIEvent evt)
+        {
+            if (evt.imguiEvent.type == EventType.DragUpdated || evt.imguiEvent.type == EventType.DragPerform)
+            {
+                var currentTarget = evt.currentTarget as VisualElement;
+                if (currentTarget == null)
+                    return;
+                var objects = DragAndDrop.objectReferences;
+                Object draggedObject = null;
+                foreach (var obj in objects)
+                {
+                    Debug.Log(obj.GetType().Name);
+                    if (ValidateObject(obj))
+                    {
+                        draggedObject = obj;
+                        break;
+                    }
+                }
+                if (draggedObject == null)
+                    return;
+
+//                Debug.LogFormat("{0}: {1}", draggedObject.GetType().Name, draggedObject.name);
+                DragAndDrop.visualMode = DragAndDropVisualMode.Generic;
+                if (evt.imguiEvent.type == EventType.DragPerform)
+                {
+                    var nodePosition = m_GraphView.contentViewContainer.transform.matrix.inverse.MultiplyPoint3x4(m_GraphView.panel.visualTree.ChangeCoordinatesTo(m_GraphView, Event.current.mousePosition));
+                    CreateNode(draggedObject, nodePosition);
+                    DragAndDrop.AcceptDrag();
+                }
+            }
+        }
+    }
+}

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Manipulators/GraphDropTarget.cs.meta

+fileFormatVersion: 2
+guid: 9fd73fb7c6eb4a04978545358d5b55d5
+timeCreated: 1509089285