feat: reduce drag line flicker with delay

Author: lukasbach

.changeset/pink-ravens-shout.md

@@ -0,0 +1,5 @@
+---
+"@headless-tree/core": patch
+---
+
+Introduced a short delay before hiding the drag line when leaving a drag target, which helps to reduce flickering of the dragline when moving between items

packages/core/src/features/drag-and-drop/feature.ts

@@ -193,6 +193,7 @@ export const dragAndDropFeature: FeatureImplementation = {
           return;
         }
         dataRef.current.lastDragCode = nextDragCode;
+        dataRef.current.lastDragEnter = Date.now();
 
         const target = getDragTarget(e, item, tree);
 
@@ -222,13 +223,16 @@ export const dragAndDropFeature: FeatureImplementation = {
       },
 
       onDragLeave: () => {
-        const dataRef = tree.getDataRef<DndDataRef>();
-        dataRef.current.lastDragCode = "no-drag";
-        tree.applySubStateUpdate("dnd", (state) => ({
-          ...state,
-          draggingOverItem: undefined,
-          dragTarget: undefined,
-        }));
+        setTimeout(() => {
+          const dataRef = tree.getDataRef<DndDataRef>();
+          if ((dataRef.current.lastDragEnter ?? 0) + 100 >= Date.now()) return;
+          dataRef.current.lastDragCode = "no-drag";
+          tree.applySubStateUpdate("dnd", (state) => ({
+            ...state,
+            draggingOverItem: undefined,
+            dragTarget: undefined,
+          }));
+        }, 100);
       },
 
       onDragEnd: (e: DragEvent) => {

packages/core/src/features/drag-and-drop/types.ts

@@ -3,6 +3,7 @@ import { ItemInstance, SetStateFn } from "../../types/core";
 export interface DndDataRef {
   lastDragCode?: string;
   lastAllowDrop?: boolean;
+  lastDragEnter?: number;
   windowDragEndListener?: () => void;
 }