Implement auto-sizing for box colliders when they are added to the scene.

Source/Editor/Modules/SceneModule.cs

@@ -534,6 +534,8 @@ namespace FlaxEditor.Modules
             {
                 node.ParentNode = parentNode;
             }
+
+            actor.OnActorSpawned();
         }
 
         private void OnActorDeleted(Actor actor)

Source/Engine/Level/Actor.cs

@@ -116,6 +116,15 @@ namespace FlaxEngine
             LocalTransform = Transform.Identity;
         }
 
+        /// <summary>
+        /// Called in-editor when an actor is added to the scene.
+        /// If not in the editor, this function will not be called.
+        /// </summary>
+        public virtual void OnActorSpawned()
+        {
+
+        }
+
         /// <summary>
         /// Creates a new child actor of the given type.
         /// </summary>

Source/Engine/Level/Actors/BoxCollider.cs

@@ -0,0 +1,27 @@
+using System;
+
+namespace FlaxEngine
+{
+    partial class BoxCollider
+    {
+        /// <inheritdoc />
+        public override void OnActorSpawned()
+        {
+            base.OnActorSpawned();
+            if (Parent is StaticModel model)
+            {
+                Vector3 modelScale = model.Scale;
+                Vector3 modelSize = model.Box.Size;
+                Vector3 modelCenter = model.Box.Center - model.Position;
+                Vector3 colliderSize = modelSize / modelScale;
+                Vector3 colliderCenter = modelCenter / modelScale;
+
+                Size = colliderSize;
+                Center = colliderCenter;
+
+                // Undo Rotation
+                Orientation *= Quaternion.Invert(Orientation);
+            }
+        }
+    }
+}