Devlog · Oct 24, 2026
Teaching zombies to stay on their feet.
In GTA IV, people didn't just play a death animation. They stumbled, grabbed the wound and caught themselves. That was NaturalMotion's Euphoria, and it still sets the bar. We're building our own version of that idea from scratch inside Arcwright, and pushing to go further. Here's where it stands this week.
01
Balance
Every character carries a balance point. The cyan dot is its centre of mass, with a line straight down to the floor. When that point leaves the space between the feet, the body has to step, or it falls. Here we walked a zombie into a post: it steps, steps again, fights to stay up, loses, and starts pushing itself back up.
02
The skeleton view
The white wire is each character's skeleton, drawn live over the body: every bone the engine moves when they're hit. We built this view to check the new muscles. Does a shot body fold at the right joints? The red line is the bullet's path, white at the muzzle fading to red, with a red dot where it hit.
03
Catching the fall
A shot character used to go limp the instant it was hit. Now it buckles, the hands go out to catch the fall, and the muscles let go one limb at a time.
04
Shot reactions
Hit in the body, a zombie reaches for the wound and staggers. The third shot drops it. A second zombie takes a leg shot.
05
Hitboxes that fit
Bullets need something to hit. Our old hitboxes covered only 33–44% of each character: a zombie in a big jacket is much wider than the shape under it, and the hands had none. Now every character's hitboxes are fitted to its own body. 85% coverage, plus the hands and the neck.
06
How the work gets checked
Claude Opus 5.5 builds inside the engine with us, and it checks what it builds. One command renders a model from every side: the final image, the wireframe and a normals map, with the hitboxes, skeleton and balance markers drawn on top. This is one of those views.
07
Getting back up
Down is not the end. A fallen zombie rolls over, gets its knees under it and stands back up.
This is an early step. Full physical reactions are next, on every zombie in our haunted mansion. Each step goes up here first. Everything on this page was recorded in the engine, on test characters in a plain lab.
Start building today.
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