用panda3d写出对话系统，给出代码。

好的，以下是一个简单的 Panda3D 对话系统的示例代码：

from direct.showbase.DirectObject import DirectObject
from direct.gui.OnscreenText import OnscreenText
from direct.gui.DirectGui import *
from panda3d.core import TextNode

class DialogSystem(DirectObject):
    def __init__(self):
        DirectObject.__init__(self)
        
        # 初始化对话框
        self.dialogBox = DirectFrame(
            frameColor=(0, 0, 0, 0.8),
            frameSize=(-1, 1, -0.2, 0.2),
            pos=(0, 0, -0.9),
            parent=base.aspect2d
        )
        self.dialogText = OnscreenText(
            text="",
            parent=self.dialogBox,
            pos=(0, 0.07),
            scale=0.07,
            fg=(1, 1, 1, 1),
            align=TextNode.ACenter,
            mayChange=True
        )
        self.dialogOptions = []
        for i in range(3):
            option = DirectButton(
                text="",
                text_scale=0.05,
                text_fg=(1, 1, 1, 1),
                frameColor=(0.5, 0.5, 0.5, 1),
                pos=(-0.4, 0, -0.1 - 0.15 * i),
                parent=self.dialogBox,
                relief=DGG.FLAT,
                command=self.onOptionSelected,
                extraArgs=[i],
                scale=1.25
            )
            self.dialogOptions.append(option)
        
        # 测试对话框
        self.currentDialog = [
            {
                "speaker": "NPC1",
                "text": "你好，我是 NPC1。",
                "options": [
                    {"text": "你好，NPC1。", "next": 1},
                    {"text": "我不想和你交谈。", "next": -1}
                ]
            },
            {
                "speaker": "NPC1",
                "text": "你想问我什么吗？",
                "options": [
                    {"text": "你是谁？", "next": -1},
                    {"text": "你有什么事吗？", "next": 2}
                ]
            },
            {
                "speaker": "NPC1",
                "text": "我需要你帮我找到一些东西。",
                "options": [
                    {"text": "好的，我会帮助你。", "next": -1},
                    {"text": "不，我没兴趣。", "next": -1}
                ]
            }
        ]
        
        # 开始对话
        self.startDialog(self.currentDialog[0])
    
    def startDialog(self, dialog):
        # 显示对话框
        self.dialogBox.show()
        self.dialogText.setText(dialog["speaker"] + ": " + dialog["text"])
        for i, option in enumerate(dialog["options"]):
            self.dialogOptions[i]["text"] = option["text"]
        for option in self.dialogOptions[len(dialog["options"]):]:
            option.hide()
    
    def endDialog(self):
        # 隐藏对话框
        self.dialogBox.hide()
    
    def onOptionSelected(self, optionIndex):
        # 处理选择的选项
        selectedOption = self.currentDialog[0]["options"][optionIndex]
        if selectedOption["next"]