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Michael G. Inso
Michael G. Inso

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⚡ How We Built a Pro-Level Esports Aim Trainer with React 19 & GPT-4o

#webdev #ai #programming #typescript

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⚡ How We Built a Pro-Level Esports Aim Trainer with React 19 & GPT-4o

Behind the code of "C9 Reflex Arena"—our Cloud9 x JetBrains Hackathon entry.

![Cover Image Placeholder: A split screen showing code on the left and the glowing neon game interface on the right]

In the world of esports, the difference between a highlight reel and a "gray screen" is measured in milliseconds. When Cloud9 and JetBrains announced a hackathon to build the ultimate fan engagement experience, we knew we couldn't just build a simple clicker game. We needed something that felt competitive, looked cyberpunk, and ran at a buttery smooth 60 FPS.

Enter C9 Reflex Arena: An adaptive reaction training ground designed for the chaotic energy of an LCS event booth.

Here’s a deep dive into how we built it using the absolute bleeding edge of web tech: React 19, Tailwind CSS v4, and AI-driven game design.

🏗️ The Stack: Living on the Edge

We decided to take a risk. Instead of using the "safe" stack, we wanted to see what the future of frontend development looked like.

  • Framework: React 19 (RC)
  • Styling: Tailwind CSS v4 (Alpha)
  • State: Spark KV + Functional Updates
  • AI: OpenAI GPT-4o-mini (via Vercel AI SDK)
  • IDE: WebStorm 2024.3 with Junie

Why React 19?

We wanted to leverage the new Compiler and Action paradigms. In a high-frequency game loop, re-renders are the enemy. React 19 allowed us to manage complex state transitions (score, combo, timer, particle count) without the "useEffect hell" that usually plagues React games.

🧠 The Secret Sauce: AI Adaptive Difficulty

Most reaction games have static difficulty settings: Easy, Medium, Hard. We wanted C9 Reflex Arena to feel like a living opponent.

We integrated GPT-4o-mini to analyze player telemetry in real-time. The game doesn't just spawn targets; it watches you.

How it works:

  1. Data Collection: The game tracks your average reaction time (ms) and accuracy (%) over a 10-target window.
  2. The Prompt: We send this batch data to the AI with a system prompt: "You are an esports coach. The player is hitting 95% accuracy with 150ms reaction time. Adjust the game parameters to challenge them without frustrating them."

  3. JSON Response: The AI returns structured JSON:

    {
  "spawnInterval": 450,
  "targetSize": 0.85,
  "message": "Too easy? Let's speed it up."
}

  4. Hot-Patching: The game state updates instantly. If you’re playing like a pro, the targets get smaller and faster. If you miss three in a row, the game slows down to help you recover your rhythm.

🎨 Styling with Tailwind v4

Tailwind v4 is a paradigm shift. Gone is the massive configuration file; everything is now native CSS variables. This was crucial for our Theme Engine.

We defined our "Cloud9 Cyberpunk" palette using OKLCH colors for maximum vibrancy on gaming monitors:

:root {
  --color-c9-blue: oklch(0.65 0.24 240);
  --color-c9-pink: oklch(0.70 0.25 350);
}
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Because v4 compiles on the fly, we could animate these variables using Framer Motion to create pulsating neon glows that react to the beat of the game without causing layout thrashing.

🤖 Coding with Junie (JetBrains AI)

Since this was a JetBrains hackathon, we leaned heavily on Junie, their new AI agent in WebStorm.

Honest review? It saved us about 30% development time.

The "killer feature" wasn't code generation—it was Contextual Refactoring. At one point, our GameCanvas.tsx file hit 600 lines. We asked Junie: "Extract the particle rendering logic into a custom hook."

Junie didn't just give us the code snippet; it analyzed the dependencies, created useParticleSystem.ts, moved the relevant useRef hooks, and updated the imports in the parent file. For a hackathon timeline, that kind of automated refactoring is invaluable.

🚀 The Result

C9 Reflex Arena is now a fully functional PWA (Progressive Web App). It features:

  • Global Leaderboards (GitHub Auth)
  • Friend Challenges (Async competition)
  • 60 FPS Performance on mobile and desktop
  • Event Ready Mode for fast booth turnover

Building this project taught us that the web is ready for high-performance gaming. React 19 handles the logic, Canvas handles the rendering, and AI handles the balance.

The code is open source. If you want to see how we wired up the AI or how Tailwind v4 works in production, check out the repo below!

*🔗 https://github.com/MiChaelinzo/untitled *
*🎮 https://untitled--MiChaelinzo.github.app *

Built with 💙 for the Cloud9 x JetBrains Hackathon.

React19 #Cloud9 #JetBrains #Hackathon #WebDev #AI

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