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

using System.Linq;
using UnityEngine;
using UnityEngine.Experimental.UIElements;
using UnityEditor.ShaderGraph;

namespace UnityEditor.ShaderGraph.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)
            {
                m_Graph.owner.RegisterCompleteObjectUndo("Drag Sub-Graph");
                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();
                }
            }
        }
    }
}