Refactor main editor viewport and prefab viewport to share dragging handling code

Source/Editor/Gizmo/IGizmoOwner.cs

@@ -106,5 +106,11 @@ namespace FlaxEditor.Gizmo
         /// </summary>
         /// <param name="nodes">The nodes to select</param>
         void Select(List<SceneGraph.SceneGraphNode> nodes);
+
+        /// <summary>
+        /// Spawns the actor in the viewport hierarchy.
+        /// </summary>
+        /// <param name="actor">The new actor to spawn.</param>
+        void Spawn(Actor actor);
     }
 }

Source/Editor/Viewport/EditorGizmoViewport.cs

@@ -86,6 +86,9 @@ namespace FlaxEditor.Viewport
         /// <inheritdoc />
         public abstract void Select(List<SceneGraphNode> nodes);
 
+        /// <inheritdoc />
+        public abstract void Spawn(Actor actor);
+
         /// <inheritdoc />
         protected override bool IsControllingMouse => Gizmos.Active?.IsControllingMouse ?? false;
 

Source/Editor/Viewport/MainEditorGizmoViewport.cs

@@ -5,9 +5,7 @@ using System.Collections.Generic;
 using FlaxEditor.Content;
 using FlaxEditor.Gizmo;
 using FlaxEditor.GUI.ContextMenu;
-using FlaxEditor.GUI.Drag;
 using FlaxEditor.SceneGraph;
-using FlaxEditor.SceneGraph.Actors;
 using FlaxEditor.Scripting;
 using FlaxEditor.Viewport.Cameras;
 using FlaxEditor.Viewport.Modes;
@@ -37,28 +35,8 @@ namespace FlaxEditor.Viewport
         private readonly ViewportWidgetButton _rotateSnapping;
         private readonly ViewportWidgetButton _scaleSnapping;
 
-        private readonly DragAssets<DragDropEventArgs> _dragAssets;
-        private readonly DragActorType<DragDropEventArgs> _dragActorType = new DragActorType<DragDropEventArgs>(ValidateDragActorType);
-
         private SelectionOutline _customSelectionOutline;
 
-        /// <summary>
-        /// The custom drag drop event arguments.
-        /// </summary>
-        /// <seealso cref="FlaxEditor.GUI.Drag.DragEventArgs" />
-        public class DragDropEventArgs : DragEventArgs
-        {
-            /// <summary>
-            /// The hit.
-            /// </summary>
-            public SceneGraphNode Hit;
-
-            /// <summary>
-            /// The hit location.
-            /// </summary>
-            public Vector3 HitLocation;
-        }
-
         /// <summary>
         /// The editor sprites rendering effect.
         /// </summary>
@@ -137,15 +115,12 @@ namespace FlaxEditor.Viewport
         private bool _lockedFocus;
         private double _lockedFocusOffset;
         private readonly ViewportDebugDrawData _debugDrawData = new ViewportDebugDrawData(32);
-        private StaticModel _previewStaticModel;
-        private int _previewModelEntryIndex;
-        private BrushSurface _previewBrushSurface;
         private EditorSpritesRenderer _editorSpritesRenderer;
 
         /// <summary>
         /// Drag and drop handlers
         /// </summary>
-        public readonly DragHandlers DragHandlers = new DragHandlers();
+        public readonly ViewportDragHandlers DragHandlers;
 
         /// <summary>
         /// The transform gizmo.
@@ -219,7 +194,7 @@ namespace FlaxEditor.Viewport
         : base(Object.New<SceneRenderTask>(), editor.Undo, editor.Scene.Root)
         {
             _editor = editor;
-            _dragAssets = new DragAssets<DragDropEventArgs>(ValidateDragItem);
+            DragHandlers = new ViewportDragHandlers(this, this, ValidateDragItem, ValidateDragActorType);
             var inputOptions = editor.Options.Options.Input;
 
             // Prepare rendering task
@@ -408,9 +383,6 @@ namespace FlaxEditor.Viewport
             ViewWidgetButtonMenu.AddSeparator();
             ViewWidgetButtonMenu.AddButton("Create camera here", CreateCameraAtView);
 
-            DragHandlers.Add(_dragActorType);
-            DragHandlers.Add(_dragAssets);
-
             // Init gizmo modes
             {
                 // Add default modes used by the editor
@@ -430,7 +402,11 @@ namespace FlaxEditor.Viewport
             InputActions.Add(options => options.TranslateMode, () => TransformGizmo.ActiveMode = TransformGizmoBase.Mode.Translate);
             InputActions.Add(options => options.RotateMode, () => TransformGizmo.ActiveMode = TransformGizmoBase.Mode.Rotate);
             InputActions.Add(options => options.ScaleMode, () => TransformGizmo.ActiveMode = TransformGizmoBase.Mode.Scale);
-            InputActions.Add(options => options.ToggleTransformSpace, () => { OnTransformSpaceToggle(transformSpaceToggle); transformSpaceToggle.Checked = !transformSpaceToggle.Checked; });
+            InputActions.Add(options => options.ToggleTransformSpace, () =>
+            {
+                OnTransformSpaceToggle(transformSpaceToggle);
+                transformSpaceToggle.Checked = !transformSpaceToggle.Checked;
+            });
             InputActions.Add(options => options.LockFocusSelection, LockFocusSelection);
             InputActions.Add(options => options.FocusSelection, FocusSelection);
             InputActions.Add(options => options.RotateSelection, RotateSelection);
@@ -530,20 +506,9 @@ namespace FlaxEditor.Viewport
 
         private void OnCollectDrawCalls(ref RenderContext renderContext)
         {
-            if (_previewStaticModel)
+            DragHandlers.CollectDrawCalls(_debugDrawData, ref renderContext);
-            {
-                _debugDrawData.HighlightModel(_previewStaticModel, _previewModelEntryIndex);
-            }
-            if (_previewBrushSurface.Brush != null)
-            {
-                _debugDrawData.HighlightBrushSurface(_previewBrushSurface);
-            }
-
             if (ShowNavigation)
-            {
                 Editor.Internal_DrawNavMesh();
-            }
-
             _debugDrawData.OnDraw(ref renderContext);
         }
 
@@ -942,78 +907,14 @@ namespace FlaxEditor.Viewport
             base.OnLeftMouseButtonUp();
         }
 
-        private void GetHitLocation(ref Float2 location, out SceneGraphNode hit, out Vector3 hitLocation, out Vector3 hitNormal)
-        {
-            // Get mouse ray and try to hit any object
-            var ray = ConvertMouseToRay(ref location);
-            var view = new Ray(ViewPosition, ViewDirection);
-            var gridPlane = new Plane(Vector3.Zero, Vector3.Up);
-            var flags = SceneGraphNode.RayCastData.FlagTypes.SkipColliders | SceneGraphNode.RayCastData.FlagTypes.SkipEditorPrimitives;
-            hit = Editor.Instance.Scene.Root.RayCast(ref ray, ref view, out var closest, out var normal, flags);
-            if (hit != null)
-            {
-                // Use hit location
-                hitLocation = ray.Position + ray.Direction * closest;
-                hitNormal = normal;
-            }
-            else if (Grid.Enabled && CollisionsHelper.RayIntersectsPlane(ref ray, ref gridPlane, out closest) && closest < 4000.0f)
-            {
-                // Use grid location
-                hitLocation = ray.Position + ray.Direction * closest;
-                hitNormal = Vector3.Up;
-            }
-            else
-            {
-                // Use area in front of the viewport
-                hitLocation = ViewPosition + ViewDirection * 100;
-                hitNormal = Vector3.Up;
-            }
-        }
-
-        private void SetDragEffects(ref Float2 location)
-        {
-            if (_dragAssets.HasValidDrag && _dragAssets.Objects[0].IsOfType<MaterialBase>())
-            {
-                GetHitLocation(ref location, out var hit, out _, out _);
-                ClearDragEffects();
-                var material = FlaxEngine.Content.LoadAsync<MaterialBase>(_dragAssets.Objects[0].ID);
-                if (material.IsDecal)
-                    return;
-
-                if (hit is StaticModelNode staticModelNode)
-                {
-                    _previewStaticModel = (StaticModel)staticModelNode.Actor;
-                    var ray = ConvertMouseToRay(ref location);
-                    _previewStaticModel.IntersectsEntry(ref ray, out _, out _, out _previewModelEntryIndex);
-                }
-                else if (hit is BoxBrushNode.SideLinkNode brushSurfaceNode)
-                {
-                    _previewBrushSurface = brushSurfaceNode.Surface;
-                }
-            }
-        }
-
-        private void ClearDragEffects()
-        {
-            _previewStaticModel = null;
-            _previewModelEntryIndex = -1;
-            _previewBrushSurface = new BrushSurface();
-        }
-
         /// <inheritdoc />
         public override DragDropEffect OnDragEnter(ref Float2 location, DragData data)
         {
-            ClearDragEffects();
+            DragHandlers.ClearDragEffects();
-
             var result = base.OnDragEnter(ref location, data);
             if (result != DragDropEffect.None)
                 return result;
-
+            return DragHandlers.DragEnter(ref location, data);
-            result = DragHandlers.OnDragEnter(data);
-
-            SetDragEffects(ref location);
-
-            return result;
         }
 
         private bool ValidateDragItem(ContentItem contentItem)
@@ -1042,167 +943,29 @@ namespace FlaxEditor.Viewport
         /// <inheritdoc />
         public override DragDropEffect OnDragMove(ref Float2 location, DragData data)
         {
-            ClearDragEffects();
+            DragHandlers.ClearDragEffects();
-
             var result = base.OnDragMove(ref location, data);
             if (result != DragDropEffect.None)
                 return result;
-
+            return DragHandlers.DragEnter(ref location, data);
-            SetDragEffects(ref location);
-
-            return DragHandlers.Effect;
         }
 
         /// <inheritdoc />
         public override void OnDragLeave()
         {
-            ClearDragEffects();
+            DragHandlers.ClearDragEffects();
-
             DragHandlers.OnDragLeave();
-
             base.OnDragLeave();
         }
 
-        private Vector3 PostProcessSpawnedActorLocation(Actor actor, ref Vector3 hitLocation)
-        {
-            // Refresh actor position to ensure that cached bounds are valid
-            actor.Position = Vector3.One;
-            actor.Position = Vector3.Zero;
-
-            // Place the object
-            //var location = hitLocation - (box.Size.Length * 0.5f) * ViewDirection;
-            var editorBounds = actor.EditorBoxChildren;
-            var bottomToCenter = actor.Position.Y - editorBounds.Minimum.Y;
-            var location = hitLocation + new Vector3(0, bottomToCenter, 0);
-
-            // Apply grid snapping if enabled
-            if (UseSnapping || TransformGizmo.TranslationSnapEnable)
-            {
-                float snapValue = TransformGizmo.TranslationSnapValue;
-                location = new Vector3(
-                                       (int)(location.X / snapValue) * snapValue,
-                                       (int)(location.Y / snapValue) * snapValue,
-                                       (int)(location.Z / snapValue) * snapValue);
-            }
-
-            return location;
-        }
-
-        private void Spawn(Actor actor, ref Vector3 hitLocation, ref Vector3 hitNormal)
-        {
-            actor.Position = PostProcessSpawnedActorLocation(actor, ref hitLocation);
-            var parent = actor.Parent ?? Level.GetScene(0);
-            actor.Name = Utilities.Utils.IncrementNameNumber(actor.Name, x => parent.GetChild(x) == null);
-            Editor.Instance.SceneEditing.Spawn(actor);
-            Focus();
-        }
-
-        private void Spawn(AssetItem item, SceneGraphNode hit, ref Float2 location, ref Vector3 hitLocation, ref Vector3 hitNormal)
-        {
-            if (item.IsOfType<MaterialBase>())
-            {
-                var material = FlaxEngine.Content.LoadAsync<MaterialBase>(item.ID);
-                if (material && !material.WaitForLoaded(100) && material.IsDecal)
-                {
-                    var actor = new Decal
-                    {
-                        Material = material,
-                        LocalOrientation = RootNode.RaycastNormalRotation(ref hitNormal),
-                        Name = item.ShortName
-                    };
-                    DebugDraw.DrawWireArrow(PostProcessSpawnedActorLocation(actor, ref hitNormal), actor.LocalOrientation, 1.0f, Color.Red, 1000000);
-                    Spawn(actor, ref hitLocation, ref hitNormal);
-                }
-                else if (hit is StaticModelNode staticModelNode)
-                {
-                    var staticModel = (StaticModel)staticModelNode.Actor;
-                    var ray = ConvertMouseToRay(ref location);
-                    if (staticModel.IntersectsEntry(ref ray, out _, out _, out var entryIndex))
-                    {
-                        using (new UndoBlock(Undo, staticModel, "Change material"))
-                            staticModel.SetMaterial(entryIndex, material);
-                    }
-                }
-                else if (hit is BoxBrushNode.SideLinkNode brushSurfaceNode)
-                {
-                    using (new UndoBlock(Undo, brushSurfaceNode.Brush, "Change material"))
-                    {
-                        var surface = brushSurfaceNode.Surface;
-                        surface.Material = material;
-                        brushSurfaceNode.Surface = surface;
-                    }
-                }
-                return;
-            }
-            if (item.IsOfType<SceneAsset>())
-            {
-                Editor.Instance.Scene.OpenScene(item.ID, true);
-                return;
-            }
-            {
-                var actor = item.OnEditorDrop(this);
-                actor.Name = item.ShortName;
-                Spawn(actor, ref hitLocation, ref hitNormal);
-            }
-        }
-
-        private void Spawn(ScriptType item, SceneGraphNode hit, ref Float2 location, ref Vector3 hitLocation, ref Vector3 hitNormal)
-        {
-            var actor = item.CreateInstance() as Actor;
-            if (actor == null)
-            {
-                Editor.LogWarning("Failed to spawn actor of type " + item.TypeName);
-                return;
-            }
-            actor.Name = item.Name;
-            Spawn(actor, ref hitLocation, ref hitNormal);
-        }
-
         /// <inheritdoc />
         public override DragDropEffect OnDragDrop(ref Float2 location, DragData data)
         {
-            ClearDragEffects();
+            DragHandlers.ClearDragEffects();
-
             var result = base.OnDragDrop(ref location, data);
             if (result != DragDropEffect.None)
                 return result;
-
+            return DragHandlers.DragDrop(ref location, data);
-            // Check if drag sth
-            Vector3 hitLocation = ViewPosition, hitNormal = -ViewDirection;
-            SceneGraphNode hit = null;
-            if (DragHandlers.HasValidDrag)
-            {
-                GetHitLocation(ref location, out hit, out hitLocation, out hitNormal);
-            }
-
-            // Drag assets
-            if (_dragAssets.HasValidDrag)
-            {
-                result = _dragAssets.Effect;
-
-                // Process items
-                for (int i = 0; i < _dragAssets.Objects.Count; i++)
-                {
-                    var item = _dragAssets.Objects[i];
-                    Spawn(item, hit, ref location, ref hitLocation, ref hitNormal);
-                }
-            }
-            // Drag actor type
-            else if (_dragActorType.HasValidDrag)
-            {
-                result = _dragActorType.Effect;
-
-                // Process items
-                for (int i = 0; i < _dragActorType.Objects.Count; i++)
-                {
-                    var item = _dragActorType.Objects[i];
-                    Spawn(item, hit, ref location, ref hitLocation, ref hitNormal);
-                }
-            }
-
-            DragHandlers.OnDragDrop(new DragDropEventArgs { Hit = hit, HitLocation = hitLocation });
-
-            return result;
         }
 
         /// <inheritdoc />
@@ -1211,6 +974,14 @@ namespace FlaxEditor.Viewport
             _editor.SceneEditing.Select(nodes);
         }
 
+        /// <inheritdoc />
+        public override void Spawn(Actor actor)
+        {
+            var parent = actor.Parent ?? Level.GetScene(0);
+            actor.Name = Utilities.Utils.IncrementNameNumber(actor.Name, x => parent.GetChild(x) == null);
+            Editor.Instance.SceneEditing.Spawn(actor);
+        }
+
         /// <inheritdoc />
         public override void OnDestroy()
         {

Source/Editor/Viewport/PrefabWindowViewport.cs

@@ -5,9 +5,7 @@ using System.Collections.Generic;
 using FlaxEditor.Content;
 using FlaxEditor.Gizmo;
 using FlaxEditor.GUI.ContextMenu;
-using FlaxEditor.GUI.Drag;
 using FlaxEditor.SceneGraph;
-using FlaxEditor.SceneGraph.Actors;
 using FlaxEditor.Scripting;
 using FlaxEditor.Viewport.Cameras;
 using FlaxEditor.Viewport.Previews;
@@ -56,9 +54,11 @@ namespace FlaxEditor.Viewport
 
         private readonly ViewportDebugDrawData _debugDrawData = new ViewportDebugDrawData(32);
         private PrefabSpritesRenderer _spritesRenderer;
-        private readonly DragAssets _dragAssets;
+
-        private readonly DragActorType _dragActorType = new DragActorType(ValidateDragActorType);
+        /// <summary>
-        private readonly DragHandlers _dragHandlers = new DragHandlers();
+        /// Drag and drop handlers
+        /// </summary>
+        public readonly ViewportDragHandlers DragHandlers;
 
         /// <summary>
         /// The transform gizmo.
@@ -81,7 +81,7 @@ namespace FlaxEditor.Viewport
             _window.SelectionChanged += OnSelectionChanged;
             Undo = window.Undo;
             ViewportCamera = new FPSCamera();
-            _dragAssets = new DragAssets(ValidateDragItem);
+            DragHandlers = new ViewportDragHandlers(this, this, ValidateDragItem, ValidateDragActorType);
             ShowDebugDraw = true;
             ShowEditorPrimitives = true;
             Gizmos = new GizmosCollection(this);
@@ -228,14 +228,15 @@ namespace FlaxEditor.Viewport
             _gizmoModeScale.Toggled += OnGizmoModeToggle;
             gizmoMode.Parent = this;
 
-            _dragHandlers.Add(_dragActorType);
-            _dragHandlers.Add(_dragAssets);
-
             // Setup input actions
             InputActions.Add(options => options.TranslateMode, () => TransformGizmo.ActiveMode = TransformGizmoBase.Mode.Translate);
             InputActions.Add(options => options.RotateMode, () => TransformGizmo.ActiveMode = TransformGizmoBase.Mode.Rotate);
             InputActions.Add(options => options.ScaleMode, () => TransformGizmo.ActiveMode = TransformGizmoBase.Mode.Scale);
-            InputActions.Add(options => options.ToggleTransformSpace, () => { OnTransformSpaceToggle(transformSpaceToggle); transformSpaceToggle.Checked = !transformSpaceToggle.Checked; });
+            InputActions.Add(options => options.ToggleTransformSpace, () =>
+            {
+                OnTransformSpaceToggle(transformSpaceToggle);
+                transformSpaceToggle.Checked = !transformSpaceToggle.Checked;
+            });
             InputActions.Add(options => options.FocusSelection, ShowSelectedActors);
 
             SetUpdate(ref _update, OnUpdate);
@@ -267,6 +268,7 @@ namespace FlaxEditor.Viewport
 
         private void OnCollectDrawCalls(ref RenderContext renderContext)
         {
+            DragHandlers.CollectDrawCalls(_debugDrawData, ref renderContext);
             _debugDrawData.OnDraw(ref renderContext);
         }
 
@@ -306,6 +308,7 @@ namespace FlaxEditor.Viewport
             var orient = ViewOrientation;
             ((FPSCamera)ViewportCamera).ShowActors(TransformGizmo.SelectedParents, ref orient);
         }
+
         /// <inheritdoc />
         public EditorViewport Viewport => this;
 
@@ -354,6 +357,12 @@ namespace FlaxEditor.Viewport
             _window.Select(nodes);
         }
 
+        /// <inheritdoc />
+        public void Spawn(Actor actor)
+        {
+            _window.Spawn(actor);
+        }
+
         /// <inheritdoc />
         protected override bool IsControllingMouse => Gizmos.Active?.IsControllingMouse ?? false;
 
@@ -669,11 +678,11 @@ namespace FlaxEditor.Viewport
         /// <inheritdoc />
         public override DragDropEffect OnDragEnter(ref Float2 location, DragData data)
         {
+            DragHandlers.ClearDragEffects();
             var result = base.OnDragEnter(ref location, data);
             if (result != DragDropEffect.None)
                 return result;
-
+            return DragHandlers.DragEnter(ref location, data);
-            return _dragHandlers.OnDragEnter(data);
         }
 
         private bool ValidateDragItem(ContentItem contentItem)
@@ -685,7 +694,6 @@ namespace FlaxEditor.Viewport
                 if (assetItem.IsOfType<MaterialBase>())
                     return true;
             }
-
             return false;
         }
 
@@ -697,86 +705,21 @@ namespace FlaxEditor.Viewport
         /// <inheritdoc />
         public override DragDropEffect OnDragMove(ref Float2 location, DragData data)
         {
+            DragHandlers.ClearDragEffects();
             var result = base.OnDragMove(ref location, data);
             if (result != DragDropEffect.None)
                 return result;
-
+            return DragHandlers.DragEnter(ref location, data);
-            return _dragHandlers.Effect;
         }
 
         /// <inheritdoc />
         public override void OnDragLeave()
         {
-            _dragHandlers.OnDragLeave();
+            DragHandlers.ClearDragEffects();
-
+            DragHandlers.OnDragLeave();
             base.OnDragLeave();
         }
 
-        private Vector3 PostProcessSpawnedActorLocation(Actor actor, ref Vector3 hitLocation)
-        {
-            // Place the object
-            //var location = hitLocation - (box.Size.Length * 0.5f) * ViewDirection;
-            var location = hitLocation;
-
-            // Apply grid snapping if enabled
-            if (UseSnapping || TransformGizmo.TranslationSnapEnable)
-            {
-                float snapValue = TransformGizmo.TranslationSnapValue;
-                location = new Vector3(
-                                       (int)(location.X / snapValue) * snapValue,
-                                       (int)(location.Y / snapValue) * snapValue,
-                                       (int)(location.Z / snapValue) * snapValue);
-            }
-
-            return location;
-        }
-
-        private void Spawn(AssetItem item, SceneGraphNode hit, ref Float2 location, ref Vector3 hitLocation)
-        {
-            if (item is BinaryAssetItem binaryAssetItem)
-            {
-                if (typeof(MaterialBase).IsAssignableFrom(binaryAssetItem.Type))
-                {
-                    if (hit is StaticModelNode staticModelNode)
-                    {
-                        var staticModel = (StaticModel)staticModelNode.Actor;
-                        var ray = ConvertMouseToRay(ref location);
-                        if (staticModel.IntersectsEntry(ref ray, out _, out _, out var entryIndex))
-                        {
-                            var material = FlaxEngine.Content.LoadAsync<MaterialBase>(item.ID);
-                            using (new UndoBlock(Undo, staticModel, "Change material"))
-                                staticModel.SetMaterial(entryIndex, material);
-                        }
-                    }
-                    return;
-                }
-            }
-            {
-                var actor = item.OnEditorDrop(this);
-                actor.Name = item.ShortName;
-                Spawn(actor, ref hitLocation);
-            }
-        }
-
-        private void Spawn(Actor actor, ref Vector3 hitLocation)
-        {
-            actor.Position = PostProcessSpawnedActorLocation(actor, ref hitLocation);
-            _window.Spawn(actor);
-            Focus();
-        }
-
-        private void Spawn(ScriptType item, SceneGraphNode hit, ref Vector3 hitLocation)
-        {
-            var actor = item.CreateInstance() as Actor;
-            if (actor == null)
-            {
-                Editor.LogWarning("Failed to spawn actor of type " + item.TypeName);
-                return;
-            }
-            actor.Name = item.Name;
-            Spawn(actor, ref hitLocation);
-        }
-
         /// <summary>
         /// Focuses the viewport on the current selection of the gizmo.
         /// </summary>
@@ -814,57 +757,11 @@ namespace FlaxEditor.Viewport
         /// <inheritdoc />
         public override DragDropEffect OnDragDrop(ref Float2 location, DragData data)
         {
+            DragHandlers.ClearDragEffects();
             var result = base.OnDragDrop(ref location, data);
             if (result != DragDropEffect.None)
                 return result;
-
+            return DragHandlers.DragDrop(ref location, data);
-            // Check if drag sth
-            Vector3 hitLocation = ViewPosition;
-            SceneGraphNode hit = null;
-            if (_dragHandlers.HasValidDrag)
-            {
-                // Get mouse ray and try to hit any object
-                var ray = ConvertMouseToRay(ref location);
-                var view = new Ray(ViewPosition, ViewDirection);
-                hit = _window.Graph.Root.RayCast(ref ray, ref view, out var closest, SceneGraphNode.RayCastData.FlagTypes.SkipColliders);
-                if (hit != null)
-                {
-                    // Use hit location
-                    hitLocation = ray.Position + ray.Direction * closest;
-                }
-                else
-                {
-                    // Use area in front of the viewport
-                    hitLocation = ViewPosition + ViewDirection * 100;
-                }
-            }
-
-            // Drag assets
-            if (_dragAssets.HasValidDrag)
-            {
-                result = _dragAssets.Effect;
-
-                // Process items
-                for (int i = 0; i < _dragAssets.Objects.Count; i++)
-                {
-                    var item = _dragAssets.Objects[i];
-                    Spawn(item, hit, ref location, ref hitLocation);
-                }
-            }
-            // Drag actor type
-            else if (_dragActorType.HasValidDrag)
-            {
-                result = _dragActorType.Effect;
-
-                // Process items
-                for (int i = 0; i < _dragActorType.Objects.Count; i++)
-                {
-                    var item = _dragActorType.Objects[i];
-                    Spawn(item, hit, ref hitLocation);
-                }
-            }
-
-            return result;
         }
 
         /// <inheritdoc />

Source/Editor/Viewport/ViewportDraggingHelper.cs

@@ -0,0 +1,257 @@
+// Copyright (c) 2012-2023 Wojciech Figat. All rights reserved.
+
+using System;
+using System.Linq;
+using FlaxEditor.Content;
+using FlaxEditor.Gizmo;
+using FlaxEditor.GUI.Drag;
+using FlaxEditor.SceneGraph;
+using FlaxEditor.SceneGraph.Actors;
+using FlaxEditor.Scripting;
+using FlaxEngine;
+using FlaxEngine.GUI;
+
+namespace FlaxEditor.Viewport
+{
+    /// <summary>
+    /// Utility to help managing dragging assets, actors and other objects into the editor viewport.
+    /// </summary>
+    public class ViewportDragHandlers : DragHandlers
+    {
+        /// <summary>
+        /// The custom drag drop event arguments.
+        /// </summary>
+        /// <seealso cref="FlaxEditor.GUI.Drag.DragEventArgs" />
+        public class DragDropEventArgs : DragEventArgs
+        {
+            /// <summary>
+            /// The hit.
+            /// </summary>
+            public SceneGraphNode Hit;
+
+            /// <summary>
+            /// The hit location.
+            /// </summary>
+            public Vector3 HitLocation;
+        }
+
+        private readonly IGizmoOwner _owner;
+        private readonly EditorViewport _viewport;
+        private readonly DragAssets<DragDropEventArgs> _dragAssets;
+        private readonly DragActorType<DragDropEventArgs> _dragActorType;
+
+        private StaticModel _previewStaticModel;
+        private int _previewModelEntryIndex;
+        private BrushSurface _previewBrushSurface;
+
+        internal ViewportDragHandlers(IGizmoOwner owner, EditorViewport viewport, Func<AssetItem, bool> validateAsset, Func<ScriptType, bool> validateDragActorType)
+        {
+            _owner = owner;
+            _viewport = viewport;
+            Add(_dragAssets = new DragAssets<DragDropEventArgs>(validateAsset));
+            Add(_dragActorType = new DragActorType<DragDropEventArgs>(validateDragActorType));
+        }
+
+        internal void ClearDragEffects()
+        {
+            _previewStaticModel = null;
+            _previewModelEntryIndex = -1;
+            _previewBrushSurface = new BrushSurface();
+        }
+
+        internal void CollectDrawCalls(ViewportDebugDrawData debugDrawData, ref RenderContext renderContext)
+        {
+            if (_previewStaticModel)
+                debugDrawData.HighlightModel(_previewStaticModel, _previewModelEntryIndex);
+            if (_previewBrushSurface.Brush != null)
+                debugDrawData.HighlightBrushSurface(_previewBrushSurface);
+        }
+
+        internal DragDropEffect DragEnter(ref Float2 location, DragData data)
+        {
+            var result = OnDragEnter(data);
+            SetDragEffects(ref location);
+            return result;
+        }
+
+        internal DragDropEffect DragMove(ref Float2 location, DragData data)
+        {
+            SetDragEffects(ref location);
+            return Effect;
+        }
+
+        internal DragDropEffect DragDrop(ref Float2 location, DragData data)
+        {
+            Vector3 hitLocation = _viewport.ViewPosition, hitNormal = -_viewport.ViewDirection;
+            SceneGraphNode hit = null;
+            if (HasValidDrag)
+            {
+                GetHitLocation(ref location, out hit, out hitLocation, out hitNormal);
+            }
+
+            var result = DragDropEffect.None;
+            if (_dragAssets.HasValidDrag)
+            {
+                result = _dragAssets.Effect;
+                foreach (var asset in _dragAssets.Objects)
+                    Spawn(asset, hit, ref location, ref hitLocation, ref hitNormal);
+            }
+            else if (_dragActorType.HasValidDrag)
+            {
+                result = _dragActorType.Effect;
+                foreach (var actorType in _dragActorType.Objects)
+                    Spawn(actorType, hit, ref location, ref hitLocation, ref hitNormal);
+            }
+
+            OnDragDrop(new DragDropEventArgs { Hit = hit, HitLocation = hitLocation });
+
+            return result;
+        }
+
+        private void SetDragEffects(ref Float2 location)
+        {
+            if (_dragAssets.HasValidDrag && _dragAssets.Objects[0].IsOfType<MaterialBase>())
+            {
+                GetHitLocation(ref location, out var hit, out _, out _);
+                ClearDragEffects();
+                var material = FlaxEngine.Content.LoadAsync<MaterialBase>(_dragAssets.Objects[0].ID);
+                if (material.IsDecal)
+                    return;
+
+                if (hit is StaticModelNode staticModelNode)
+                {
+                    _previewStaticModel = (StaticModel)staticModelNode.Actor;
+                    var ray = _viewport.ConvertMouseToRay(ref location);
+                    _previewStaticModel.IntersectsEntry(ref ray, out _, out _, out _previewModelEntryIndex);
+                }
+                else if (hit is BoxBrushNode.SideLinkNode brushSurfaceNode)
+                {
+                    _previewBrushSurface = brushSurfaceNode.Surface;
+                }
+            }
+        }
+
+        private void GetHitLocation(ref Float2 location, out SceneGraphNode hit, out Vector3 hitLocation, out Vector3 hitNormal)
+        {
+            // Get mouse ray and try to hit any object
+            var ray = _viewport.ConvertMouseToRay(ref location);
+            var view = new Ray(_viewport.ViewPosition, _viewport.ViewDirection);
+            var gridPlane = new Plane(Vector3.Zero, Vector3.Up);
+            var flags = SceneGraphNode.RayCastData.FlagTypes.SkipColliders | SceneGraphNode.RayCastData.FlagTypes.SkipEditorPrimitives;
+            hit = _owner.SceneGraphRoot.RayCast(ref ray, ref view, out var closest, out var normal, flags);
+            var girdGizmo = (GridGizmo)_owner.Gizmos.FirstOrDefault(x => x is GridGizmo);
+            if (hit != null)
+            {
+                // Use hit location
+                hitLocation = ray.Position + ray.Direction * closest;
+                hitNormal = normal;
+            }
+            else if (girdGizmo != null && girdGizmo.Enabled && CollisionsHelper.RayIntersectsPlane(ref ray, ref gridPlane, out closest) && closest < 4000.0f)
+            {
+                // Use grid location
+                hitLocation = ray.Position + ray.Direction * closest;
+                hitNormal = Vector3.Up;
+            }
+            else
+            {
+                // Use area in front of the viewport
+                hitLocation = view.GetPoint(100);
+                hitNormal = Vector3.Up;
+            }
+        }
+
+        private Vector3 PostProcessSpawnedActorLocation(Actor actor, ref Vector3 hitLocation)
+        {
+            // Refresh actor position to ensure that cached bounds are valid
+            actor.Position = Vector3.One;
+            actor.Position = Vector3.Zero;
+
+            // Place the object
+            //var location = hitLocation - (box.Size.Length * 0.5f) * ViewDirection;
+            var editorBounds = actor.EditorBoxChildren;
+            var bottomToCenter = actor.Position.Y - editorBounds.Minimum.Y;
+            var location = hitLocation + new Vector3(0, bottomToCenter, 0);
+
+            // Apply grid snapping if enabled
+            var transformGizmo = (TransformGizmo)_owner.Gizmos.FirstOrDefault(x => x is TransformGizmo);
+            if (transformGizmo != null && (_owner.UseSnapping || transformGizmo.TranslationSnapEnable))
+            {
+                float snapValue = transformGizmo.TranslationSnapValue;
+                location = new Vector3(
+                                       (int)(location.X / snapValue) * snapValue,
+                                       (int)(location.Y / snapValue) * snapValue,
+                                       (int)(location.Z / snapValue) * snapValue);
+            }
+
+            return location;
+        }
+
+        private void Spawn(Actor actor, ref Vector3 hitLocation, ref Vector3 hitNormal)
+        {
+            actor.Position = PostProcessSpawnedActorLocation(actor, ref hitLocation);
+            _owner.Spawn(actor);
+            _viewport.Focus();
+        }
+
+        private void Spawn(ScriptType item, SceneGraphNode hit, ref Float2 location, ref Vector3 hitLocation, ref Vector3 hitNormal)
+        {
+            var actor = item.CreateInstance() as Actor;
+            if (actor == null)
+            {
+                Editor.LogWarning("Failed to spawn actor of type " + item.TypeName);
+                return;
+            }
+            actor.Name = item.Name;
+            Spawn(actor, ref hitLocation, ref hitNormal);
+        }
+
+        private void Spawn(AssetItem item, SceneGraphNode hit, ref Float2 location, ref Vector3 hitLocation, ref Vector3 hitNormal)
+        {
+            if (item.IsOfType<MaterialBase>())
+            {
+                var material = FlaxEngine.Content.LoadAsync<MaterialBase>(item.ID);
+                if (material && !material.WaitForLoaded(500) && material.IsDecal)
+                {
+                    var actor = new Decal
+                    {
+                        Material = material,
+                        LocalOrientation = RootNode.RaycastNormalRotation(ref hitNormal),
+                        Name = item.ShortName
+                    };
+                    DebugDraw.DrawWireArrow(PostProcessSpawnedActorLocation(actor, ref hitNormal), actor.LocalOrientation, 1.0f, Color.Red, 1000000);
+                    Spawn(actor, ref hitLocation, ref hitNormal);
+                }
+                else if (hit is StaticModelNode staticModelNode)
+                {
+                    var staticModel = (StaticModel)staticModelNode.Actor;
+                    var ray = _viewport.ConvertMouseToRay(ref location);
+                    if (staticModel.IntersectsEntry(ref ray, out _, out _, out var entryIndex))
+                    {
+                        using (new UndoBlock(_owner.Undo, staticModel, "Change material"))
+                            staticModel.SetMaterial(entryIndex, material);
+                    }
+                }
+                else if (hit is BoxBrushNode.SideLinkNode brushSurfaceNode)
+                {
+                    using (new UndoBlock(_owner.Undo, brushSurfaceNode.Brush, "Change material"))
+                    {
+                        var surface = brushSurfaceNode.Surface;
+                        surface.Material = material;
+                        brushSurfaceNode.Surface = surface;
+                    }
+                }
+                return;
+            }
+            if (item.IsOfType<SceneAsset>())
+            {
+                Editor.Instance.Scene.OpenScene(item.ID, true);
+                return;
+            }
+            {
+                var actor = item.OnEditorDrop(this);
+                actor.Name = item.ShortName;
+                Spawn(actor, ref hitLocation, ref hitNormal);
+            }
+        }
+    }
+}