feat: add four-direction quick-add controls to selected nodes

src/components/canvas/material-node.tsx

@@ -2,11 +2,14 @@
 
 import { createContext, useContext } from "react";
 import { Handle, Position, type NodeProps } from "@xyflow/react";
-import { FileText, Image as ImageIcon, Type } from "lucide-react";
-import type { CanvasNode } from "@/lib/canvas";
+import { FileText, Image as ImageIcon, Plus, Type } from "lucide-react";
+import { nodeDirections, type CanvasNode, type NodeDirection } from "@/lib/canvas";
 import styles from "./canvas.module.css";
 
-export const NodeEditing = createContext({ begin: () => {}, edit: (_id: string, _text: string) => {} });
+export const NodeEditing = createContext({ begin: () => {}, edit: (_id: string, _text: string) => {}, branch: (_id: string, _direction: NodeDirection) => {} });
+
+const positions = { top: Position.Top, right: Position.Right, bottom: Position.Bottom, left: Position.Left };
+const labels = { top: "上方", right: "右侧", bottom: "下方", left: "左侧" };
 
 export function MaterialNode({ id, data, selected }: NodeProps<CanvasNode>) {
   const editing = useContext(NodeEditing);
@@ -14,12 +17,21 @@ export function MaterialNode({ id, data, selected }: NodeProps<CanvasNode>) {
   return (
     <article className={`${styles.node} ${selected ? styles.selectedNode : ""}`}>
       <header className={styles.nodeHeading}><Icon size={13} /><span>{data.title}</span></header>
-      <Handle type="target" position={Position.Left} />
+      <Handle type="target" position={Position.Left} className={styles.legacyHandle} isConnectable={false} />
       {data.kind === "image" ? <img className={styles.image} src={data.src} alt={data.title} draggable={false} referrerPolicy="no-referrer" /> : (
         <textarea className="nodrag nowheel" aria-label={data.title} placeholder={data.kind === "script" ? "写下你的脚本…" : "留住一个想法…"}
           value={data.text} maxLength={100000} onFocus={editing.begin} onChange={(event) => editing.edit(id, event.target.value)} />
       )}
-      <Handle type="source" position={Position.Right} />
+      <Handle type="source" position={Position.Right} className={styles.legacyHandle} isConnectable={false} />
+      {nodeDirections.map((direction) => <Handle key={direction} id={direction} type="source" position={positions[direction]} />)}
+      {selected && nodeDirections.map((direction) => (
+        <button key={direction} type="button" className={`${styles.branchButton} ${styles["branch_" + direction]} nodrag nopan`}
+          aria-label={`在${labels[direction]}添加节点`} title={`在${labels[direction]}添加节点并连线`}
+          onPointerDown={(event) => event.stopPropagation()}
+          onClick={(event) => { event.stopPropagation(); editing.branch(id, direction); }}>
+          <Plus size={16} strokeWidth={1.6} aria-hidden="true" />
+        </button>
+      ))}
     </article>
   );
 }