Why We Built a Bullet-Heaven Survival Game with Zero Art Assets (Introducing Antumbra)

Let’s be honest: the bullet-heaven survival genre is incredible right now. There is something deeply satisfying about starting as a fragile character and slowly transforming into an unstoppable, screen-clearing force of nature.

But when our team at Hexapixora sat down to build Antumbra—our own take on the bullet-heaven survival action genre—we knew we had to do something completely different to stand out. We didn't just want to make another game with pre-rendered sprites and downloaded sound packs. We wanted absolute, mathematical control over every single pixel and sound wave.

So, we gave ourselves an insane challenge: build an entire game without a single art or audio asset.

Here is a behind-the-scenes look at what Antumbra is, how it plays, and the crazy tech we’re using to bring it to life.

What is Antumbra?

At its core, Antumbra is a fast-paced, high-stakes survival action game. You are dropped into a void, surrounded by a relentless swarm of geometric enemies. Firing is automatic, meaning your only job is to survive. You have to weave through the chaos, manage your dash ability to escape tight corners, and collect experience to draft powerful upgrades.

Right now, the game features:

• 7 distinct, upgradable weapons to craft your perfect build.

• 7 unique enemy types that force you to constantly change your strategy.

• Intense boss encounters that drop in on a rapid 60-second cadence to keep the pressure high.

• Permanent progression, so every run makes you just a little bit stronger for the next one.

It’s fast, it’s punishing, and it’s incredibly addictive. But what really makes Antumbra special is what’s happening under the hood.

The "Zero Asset" Philosophy

We built Antumbra using Flutter and Flame. Usually, developers load up their game engines with massive folders full of textures and audio clips. We decided to write algorithms instead.

Why? Because when you generate everything with code, you unlock a level of dynamic responsiveness that static files just can't match.

Procedural Neon Visuals That Pop

We want the screen to be a chaotic, beautiful mess, but you still need to be able to see what’s going to kill you. To solve this, we built a custom two-pass bloom renderer.

The game draws the scene twice: first as a blurred, intensely bright glow, and then a second time as sharp, readable shapes on top. The result is a gorgeous neon aesthetic that looks incredibly premium. And because it's all math, it's insanely fast. By batching our particle rendering, we can put 1,400 glowing particles on the screen using only 7 draw calls. It runs like absolute butter.

Synthesizing Every Single Shot

Playing the exact same gunshot sound effect 1,000 times a minute gets annoying fast. Because Antumbra has no audio files, we built a custom synthesizer directly into the game.

It generates 16-bit PCM audio in real-time. Every time you fire a weapon or an enemy explodes, the game generates the sound with slight, random variations. You never hear the exact same sample twice. Add in a generative, pulsing synth soundtrack that crossfades seamlessly, and the audio experience becomes deeply hypnotic.

The Road Ahead

Tech tricks are cool, but at the end of the day, a game has to feel good to play. We’ve spent hours putting the simulation through a brutal automated testing gauntlet (our test suite literally drives a player in circles for minutes at 60fps to ensure the game doesn't break at maximum chaos).

Right now, we are fine-tuning the difficulty curves, polishing the core loop, and making sure the "game feel" is perfect before we start adding new biomes and weapon evolutions.

We can’t wait to show you more of Antumbra in action. We’ll be sharing more devlogs about our journey building a game entirely out of code, so be sure to bookmark this page and follow Hexapixora for future updates!

Are you excited to try a pure-code survival game? Let us know what features you'd love to see in the comments below!