Kahani World — describe a scene, walk into it

An AI game studio that runs while you play. Type one sentence — "a rain-flooded night market in Mumbai, I'm a courier carrying a tiffin box someone will kill for" — and thirty seconds later you're walking through that world with arrow keys: an isometric street painted by Nano Banana 2 Lite, a player character forged in the same art style, buildings you can enter, characters who speak to you out loud, and one hidden mystery that converges to a finale.

Why this needs NB2 Lite (generation is load-bearing)

This is not a prompt-box-to-image app. The game cannot exist without fast, cheap, high-volume generation:

• Every visible thing is generated at play-time: the street, the player sprite, every interior, the finale frame. Nothing is pre-made.
• Spatial prefetch: the moment the street appears, all 3 interiors generate in parallel while you walk — so pressing E at a door is instant. The HUD shows it live: "rooms pre-building 2/3" → "all rooms pre-built · doors open instantly."
• A single 5-minute run fires ~20+ model calls (level-design text, image renders, vision passes, dialogue turns, TTS lines) — visible in the in-game "AI generations this run" ticker. At $0.034 / 1k images, a full playthrough costs well under a rupee.

The pipeline per scene

Dialogue: each NPC guards one clue of the world's single mystery. Conversations are bounded — the clue must surface by the second exchange and the chat closes by the third. NPC lines are voiced with Sarvam Bulbul v3. Collect all 3 clues → "Unravel the truth" → a generated finale frame + the secret, spoken aloud.

Google AI stack used

Model	Role
gemini-3.1-flash-lite-image (NB2 Lite)	streets, interiors, sprite, finale — all live
gemini-3.5-flash	universe + story arc, level design, walkability vision, NPC dialogue
Sarvam Bulbul v3	every NPC line + the finale, spoken

Run it

npm install
cp .env.example .env.local   # add GEMINI_API_KEY, SARVAM_API_KEY, Supabase keys, model ids
npm run dev                  # http://localhost:3000

Auth is required: unauthenticated visitors are sent to /login. Generation APIs return 401 without a valid Supabase session.

Controls: WASD / arrows move · E enter / talk · 1–3 replies · type anything to any character · Esc leave.

Auth (Supabase)

Sign-in supports Google and email magic link. Configure once:

1. Create a Supabase project.
2. Copy Project URL and publishable key (sb_publishable_...) into .env.local as NEXT_PUBLIC_SUPABASE_URL and NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY.
3. Authentication → URL Configuration
   • Site URL: http://localhost:3000
   • Redirect URLs: http://localhost:3000/auth/callback (add your production origin + /auth/callback when you deploy)
4. Authentication → Providers → Google — enable and paste a Google Cloud OAuth Client ID + Secret. In Google Cloud, set the authorized redirect URI to https://<project-ref>.supabase.co/auth/v1/callback.
5. Authentication → Providers → Email — enable magic links (passwordless). You can disable email+password if you only want OTP/magic link.

After sign-in, PKCE lands on /auth/callback, exchanges the code for a session cookie, then redirects into the game.

Database & storage (game persistence)

Run the SQL migration once in the Supabase dashboard (SQL Editor → paste supabase/migrations/0001_games.sql):

• profiles — per-user flags (is_unlimited bypasses the free creation limit)
• games — bible, premise, sprite/finale URLs, thumbnail
• game_scenes — saved overworld + interior frames
• game-assets Storage bucket (public read via URL; no broad Storage API listing)

After your first sign-in, grant yourself unlimited generation:

update public.profiles set is_unlimited = true where id = '<your-auth-user-uuid>';

Set FREE_GAME_LIMIT=0 in .env.local to disable new world creation for free users (gallery-only mode).

Impact in India

Kahani ("story") turns any Indian setting — a Chandni Chowk gali, Kerala backwaters, a Himalayan pilgrimage — into a playable, voiced world in seconds, with zero art budget. That unlocks: regional storytelling and folklore preservation in any of India's languages (swap the TTS voice), game-based learning where a classroom describes a historical scene and walks through it, and a path for India's indie game developers — the cost of world art drops from lakhs to paise.

Project map

Path	Role
lib/world-engine.ts	universe/story/scene/sprite/dialogue/voice/finale generation
lib/supabase/*	browser/server/proxy Supabase clients + requireUser()
proxy.ts	session refresh; redirect unauthenticated users to /login
app/login · app/auth/callback	Google / magic-link sign-in
app/api/games/* · app/api/profile	saved worlds REST API + creation quota
app/play/[gameId]	load a saved world (create starts on Home)
components/Home.tsx	gallery-forward landing + create entry
components/World.tsx	orchestrator: scene cache, parallel prefetch, clues, finale, persistence
components/GameCanvas.tsx	canvas loop: movement, collision, hotspots, sprite
components/DialogueBox.tsx	voiced NPC conversations
docs/	PRD, design brief, game design