Prefab brush for Instantiating a selected prefab in editor. Moved the old functionality to PrefabRandomBrush.cs (Unity-Technologies#184)

* Add new prefab brush. Moved the old functionality to PrefabRandomBrush.cs

* Add new summary for fields and methods

* Fix custom editor

* Add base class for general logic of PrefabBrushes

Author: vladderb

Editor/Brushes/PrefabBrush/PrefabBrush.cs

@@ -0,0 +1,92 @@
+using UnityEngine;
+
+namespace UnityEditor.Tilemaps
+{ 
+    /// <summary>
+    /// This base class for PrefabBrushes that contains common functionality
+    /// </summary>
+    public class BasePrefabBrush : GridBrush
+    {   /// <summary>
+        /// Anchor Point of the Instantiated Prefab in the cell when painting
+        /// </summary>
+        public Vector3 m_Anchor = new Vector3(0.5f, 0.5f, 0.5f);
+
+        /// <summary>
+        /// GameObject to instantiating
+        /// </summary>
+        protected GameObject Prefab = null;
+        
+        protected static Transform GetObjectInCell(GridLayout grid, Transform parent, Vector3Int position)
+        {
+            var childCount = parent.childCount;
+            for (var i = 0; i < childCount; i++)
+            {
+                var child = parent.GetChild(i);
+                if (position == grid.WorldToCell(child.position))
+                {
+                    return child;
+                }
+            }
+            return null;
+        }
+
+        public override void Erase(GridLayout grid, GameObject brushTarget, Vector3Int position)
+        {
+            if (brushTarget.layer == 31)
+            {
+                return;
+            }
+                
+            var erased = GetObjectInCell(grid, brushTarget.transform, position);
+            if (erased != null)
+            {
+                Undo.DestroyObjectImmediate(erased.gameObject);
+            }
+        }
+
+        public override void Paint(GridLayout grid, GameObject brushTarget, Vector3Int position)
+        {
+            // Do not allow editing palettes
+            if (brushTarget.layer == 31 || brushTarget == null)
+                return;
+            
+            var tileObject = GetObjectInCell(grid, brushTarget.transform, position);
+            if (tileObject)
+            {
+                return;
+            }
+            var instance = (GameObject)PrefabUtility.InstantiatePrefab(Prefab);
+            if (instance != null)
+            {
+                Undo.MoveGameObjectToScene(instance, brushTarget.scene, "Paint Prefabs");
+                Undo.RegisterCreatedObjectUndo((Object)instance, "Paint Prefabs");
+                instance.transform.SetParent(brushTarget.transform);
+                instance.transform.position = grid.LocalToWorld(grid.CellToLocalInterpolated(position + m_Anchor));
+            }
+        }
+    }
+    
+    public class BasePrefabBrushEditor :  GridBrushEditor
+    {
+        private SerializedProperty m_Anchor;
+        protected SerializedObject m_SerializedObject;
+
+        protected override void OnEnable()
+        {
+            base.OnEnable();
+            m_SerializedObject = new SerializedObject(target);
+            m_Anchor = m_SerializedObject.FindProperty("m_Anchor");
+        }
+
+        /// <summary>
+        /// Callback for painting the inspector GUI for the PrefabBrush in the Tile Palette.
+        /// The PrefabBrush Editor overrides this to have a custom inspector for this Brush.
+        /// </summary>
+        public override void OnPaintInspectorGUI()
+        {
+            m_SerializedObject.UpdateIfRequiredOrScript();
+            EditorGUILayout.PropertyField(m_Anchor);
+            m_SerializedObject.ApplyModifiedPropertiesWithoutUndo();
+        }
+    }
+}

Editor/Brushes/PrefabBrush.meta renamed to Editor/Brushes/PrefabBrushes.meta

@@ -0,0 +1,91 @@
+using UnityEngine;
+
+namespace UnityEditor.Tilemaps
+{
+    /// <summary>
+    /// This Brush instances and places a selected prefab onto the targeted location and parents the instanced object to the paint target.
+    /// </summary>
+    [CreateAssetMenu(fileName = "Prefab brush", menuName = "Brushes/Prefab brush")]
+    [CustomGridBrush(false, true, false, "Prefab Brush")]
+    public class PrefabBrush : BasePrefabBrush
+    {
+        /// <summary>
+        /// The selection of Prefab to paint from
+        /// </summary>
+        public GameObject m_Prefab;
+        /// <summary>
+        /// Use to remove all prefabs in the cell or just the one that is currently selected in m_Prefab
+        /// </summary>
+        public bool m_ForceDelete;
+        /// <summary>
+        /// Paints Prefabs into a given position within the selected layers.
+        /// The PrefabBrush overrides this to provide Prefab painting functionality.
+        /// </summary>
+        /// <param name="grid">Grid used for layout.</param>
+        /// <param name="brushTarget">Target of the paint operation. By default the currently selected GameObject.</param>
+        /// <param name="position">The coordinates of the cell to paint data to.</param>
+        
+        public override void Paint(GridLayout grid, GameObject brushTarget, Vector3Int position)
+        {
+            
+           
+            Prefab = m_Prefab;
+            var tileObject = GetObjectInCell(grid, brushTarget.transform, position);
+            if (tileObject == null || tileObject.name != m_Prefab.name)
+            {
+                base.Paint(grid, brushTarget, position);
+            }
+        }
+
+        /// <summary>
+        /// Erases all Prefabs in a given position within the selected layers if ForceDelete is true.
+        /// Erase only selected Prefabs in a given position within the selected layers if ForceDelete is false.
+        /// The PrefabBrush overrides this to provide Prefab erasing functionality.
+        /// </summary>
+        /// <param name="grid">Grid used for layout.</param>
+        /// <param name="brushTarget">Target of the erase operation. By default the currently selected GameObject.</param>
+        /// <param name="position">The coordinates of the cell to erase data from.</param>
+        public override void Erase(GridLayout grid, GameObject brushTarget, Vector3Int position)
+        {
+            var erased = GetObjectInCell(grid, brushTarget.transform, position);
+            if (erased == null)
+            {
+                return;
+            }
+            if (m_ForceDelete || (!m_ForceDelete && erased.gameObject.name == m_Prefab.name))
+            {
+                base.Erase(grid, brushTarget, position);
+            }
+        }
+    }
+
+    /// <summary>
+    /// The Brush Editor for a Prefab Brush.
+    /// </summary>
+    [CustomEditor(typeof(PrefabBrush))]
+    public class PrefabBrushEditor : BasePrefabBrushEditor
+    {
+        private SerializedProperty m_Prefab;
+        private SerializedProperty m_ForceDelete;
+
+        protected override void OnEnable()
+        {
+            base.OnEnable();
+            m_Prefab = m_SerializedObject.FindProperty("m_Prefab");
+            m_ForceDelete = m_SerializedObject.FindProperty("m_ForceDelete");
+        }
+
+        /// <summary>
+        /// Callback for painting the inspector GUI for the PrefabBrush in the Tile Palette.
+        /// The PrefabBrush Editor overrides this to have a custom inspector for this Brush.
+        /// </summary>
+        public override void OnPaintInspectorGUI()
+        {
+            base.OnPaintInspectorGUI();
+            m_SerializedObject.UpdateIfRequiredOrScript();
+            EditorGUILayout.PropertyField(m_Prefab, true);
+            EditorGUILayout.PropertyField(m_ForceDelete, true);
+            m_SerializedObject.ApplyModifiedPropertiesWithoutUndo();
+        }
+    }
+}