Chrono Trotter: an Android shoot 'em up made with AI

After the brick breaker Brick Trotter, I wanted a second game in the same family, this time a horizontal shoot 'em up, the kind where the ship flies to the right and everything comes at you. Chrono Trotter is an Android game where invaders travel through time to conquer History, and your ship chases them across 20 eras, from the dinosaurs to the year 3000. I built it with Godot, art generated with Gemini and Claude Code as my copilot. Every screenshot comes from the real game.

The game

You play with the phone in landscape: slide your finger anywhere on the screen, the ship follows and fires by itself. Enemies come in waves (in a line, in a V, as a wall, as a swarm), some stop to shoot and others dive at the ship. Time pylons block the way, but they also stop enemy fire.

• 20 eras: Cretaceous, Lascaux, Stonehenge, Mesopotamia, Egypt, Bell Beakers, Etruscans, Ancient Greece, Imperial China, the Roman Empire, Vikings, medieval France, the Inca Empire, the Renaissance, the Pilgrims, Pirates, the Wild West, Paris 1889, the Moon and the future.
• Projectiles from each era: rocks, arrows, spears, catapult boulders that fall in an arc, spinning axes, cannonballs, exploding pumpkins, electric beams.
• 5 giant bosses at the end of each age: the Lamassu, the Lernaean Hydra, the Dragon, the Kraken and the Mothership. You can read their health on the monster itself: it turns red and smokes as it takes hits.
• 7 power-ups: double shot, spread shot, piercing laser, shield, mega bomb, time stop and extra life.
• A ship that evolves: after each boss it takes a new shape, silver, gold, armoured red, then blue.

Harder and harder

Waves get bigger, enemies faster and obstacles more frequent. Each era brings a new attack, announced at the start of the level. From level 13, any invader can dive at the ship, and bosses get more aggressive at two thirds and one third of their health.

A grand finale

Once all 20 eras are freed, the ship takes off, the 20 postcards of the places you visited appear and the fireworks go off. Then you can start again from the dinosaurs, faster, keeping your score.

Art by Gemini and ChatGPT

The 21 backgrounds (the 20 eras and the menu), every enemy, the 5 bosses and the power-ups were generated with Gemini, from prompts I wrote with Claude: characters in profile, facing left, on a magenta background that the game cuts out by itself. The ships came from ChatGPT, based on my own drawings. One rule I set from the start: no round explosions. Enemies crumble into dust, with sparks in the monster's colour.

Synthesised sound

As in Brick Trotter, there is no audio file at all: a synthesiser written inside the game makes the soft lasers, the chime of the combos (every enemy shot down in a row goes up one note) and the music. The first version sounded too much like a piano; the second one uses bells and soft voices.

Tested by an autopilot

Claude Code wrote the code in GDScript and added a test mode: an autopilot plays the 20 levels in a row, headless and sped up, and flags the levels that drag on. The same mode takes the Google Play screenshots at 1920 × 1080 in every language, without touching the phone.

The tech stack

• Engine: Godot 4.7, code in GDScript, «Compatibility» renderer so it runs on most phones.
• Languages: Spanish, English, French, Portuguese, German and Italian, from the phone or chosen in the settings.
• Privacy: no internet, no ads and no data collected. Designed for players aged 9 and up.

Where to play it?

Chrono Trotter has just entered closed testing on Google Play: before release, Google requires at least 12 testers for 14 days in a row. I explain how it works in publishing on Google Play: the 12 testers, 14 days rule, and the full method in making an Android game with Godot. If you have an Android phone, you can sign up below.

It's the third game in the series, after Rania and Brick Trotter. For your own projects, see my custom software service.