Paris 1788

LLM chatbot NPC in engine

Self-hosted LLM implementation using Python, FastAPI and Unity for NPC conversations.

Demonstrates:
Technical Implementation

Role:
Solo Dev

Technical Implementation

Challenge

Implementing a large language model API into my own Unity / Unreal project without a paid subscription or dependency on a non-open-source provider. —> self-hosting. The AI should

Enact a specific NPC’s personality
Have access to custom and setting-specific background knowledge
Be able to recall and reference the chat history

Solution

First, I set up a Jupyter Notebook that would later host my AI.

			
mkdir "Ollama Paris Chatbot"
cd "Ollama Paris Chatbot"

For many of my next steps, Python is required. Install if uninstalled and create an .venv environment with Python as my interpreter. Navigate to the virtual environment where I will install some essentials for hosting my LLM of choice, “Ollama”.

.\.venv\Scripts\activate

			
pip install fastapi uvicorn[standard]
pip install langchain-ollama
pip install langchain-core
pip install fastapi[dev]

From that point on, I am able to host my script with my LLM. Let’s set up a new Python file that will act as a server. It will require

some references, among which lies my upcoming chatbot
the ability to ask my LLM a question with a history
the ability to clear my history when restarting the chat in-game

			
from fastapi import FastAPI
from chatbot import RAGChatBot
app = FastAPI()
@app.get("/getanswer/{request}")
def get_answer(request):
    chatbot = RAGChatBot()
    response = chatbot.ask(question=request, session_id="default")
    
    return "Vivienne says: " + response
@app.get("/clearhistory")
def clear():
    chatbot.clear_history
    return "History Cleared"

		

For my chatbot to know some specific facts, I set up a folder with a few relevant text files populated with custom and general information about the time and setting “Paris 1788”, along with a “knowledge_retriever.py” script:

			
from langchain_chroma import Chroma
from langchain_core.documents import Document
from langchain_ollama import OllamaEmbeddings
import os
documents_folder = 'paris_knowledge'
docs = []
embedding_model = OllamaEmbeddings(model='mxbai-embed-large:latest')
for filename in os.listdir(documents_folder):
    if filename.endswith('.txt'):
        with open(os.path.join(documents_folder, filename), 'r') as textfile:
            # print('Contents of', filename)
            # print(content)
            content = textfile.read()
            doc = Document(page_content = filename + content)
            docs.append(doc)
vector_database = Chroma(collection_name='paris', persist_directory='paris_db', embedding_function=embedding_model)
vector_database.add_documents(docs)
retriever = vector_database.as_retriever()

		

This was the last thing required for my “chatbot.py” to be ready for implementation. There you can find a system prompt about how the AI has to respond

			
from langchain_ollama.llms import OllamaLLM
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_core.messages import HumanMessage, AIMessage
from langchain_core.runnables.history import RunnableWithMessageHistory
from langchain_community.chat_message_histories import ChatMessageHistory
from knowledge_retriever import retriever
class RAGChatBot:
    def __init__(self, model_name='llama3.2:latest'):
        self.model = OllamaLLM(model=model_name)
        self.store = {}  # Dictionary to store chat sessions
        
        # Proper LangChain prompt template with message history placeholder
        self.prompt = ChatPromptTemplate.from_messages([
            ("system",'''[...]'''),
            # system prompt includes instructions for how the AI should behave, and what it has to do
            MessagesPlaceholder(variable_name="history"),
            ("human", """{question}""")
        ])
        
        # Create the chain
        self.chain = self.prompt | self.model
        
        # Wrap with message history
        self.chain_with_history = RunnableWithMessageHistory(
            self.chain,
            self.get_session_history,
            input_messages_key="question",
            history_messages_key="history",
        )
    
    def get_session_history(self, session_id: str) -> ChatMessageHistory:
        """Get or create chat history for a session"""
        if session_id not in self.store:
            self.store[session_id] = ChatMessageHistory()
        return self.store[session_id]
    
    def ask(self, question: str, session_id: str = "default"):
        """Ask a question with proper history handling"""
        # Retrieve relevant documents
        documents = retriever.invoke(question)
        
        # Invoke with history
        response = self.chain_with_history.invoke(
            {
                "question": question,
                "documents": documents
            },
            config={"configurable": {"session_id": session_id}}
        )
        
        return response
    
    def clear_history(self, session_id: str = "default"):
        """Clear history for a session"""
        if session_id in self.store:
            self.store[session_id].clear()
            print(f"History cleared for session: {session_id}")

		

Now just activate the server!

fastapi dev server.py #(strg + c stops the server)

I can now set up my project(s). I won’t show the whole setup, but this is the web requester necessary architecture to fetch what I am providing in my hosted server.

unity c# script relevant lines include:

			
using UnityEngine.Networking;
[...]
IEnumerator AwaitRequest()
    {
        UnityWebRequest request = UnityWebRequest.Get("http://127.0.0.1:8000/request-string");
        loading = true;
        yield return request.SendWebRequest();
        string answer = request.downloadHandler.text;
        [...]
    }
[...]

		

The “request-string” can be one of the above-defined methods, “getanswer” or “clearhistory“.

In UE5, I didn’t create a front end, but the web requester equivalent is the “Call URL” node:

Oskar Lazar : : System Designer – Programmer

Paris 1788

Paris 1788

Challenge

Solution

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Paris 1788

Paris 1788

Challenge

Solution

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