AI-written 3D campfire, 6.1 million cells, comment section erupts over 'real-time'

A campfire video has been circulating on X over the past two days. It's not a camping video; it's a 3D combustion simulation written by a developer named Leon Lin using AI.

In his post, he said: I made some realistic fire with Opus 5.5 (an AI model). A real 3D combustion simulation, 6.1 million grid cells, with flame color coming from blackbody physics, plus sparks and embers. No assets or sound files were used.

At first glance, it's easy to mistake it for live-action footage. The brightness and flicker of the flames, sparks bursting out from gaps between the logs, and crackling sounds in the background. These are not things from an asset library: no textures, no recordings—everything is computed by the program.

The flame color comes from blackbody physics, meaning the color is determined by temperature—high-temperature areas turn white, then yellow, then orange-red. This matches the mechanism of real flames; it is not an artist hand-tuning gradients. With 6.1 million grid cells, every cell is participating in the computation.

The comment section is more interesting than the video.

Someone said that after seeing too many orange plastic fake fires, this one finally looks like real heat flickering. Someone said that while rendering it, their integrated graphics card almost burned up. Someone said we need FireBench. Someone said: make a blacksmithing game now.

Some were more skeptical.

The original post never said “real-time” from beginning to end. Reposter Mark Kretschmann said it is real-time rendering, not an AI video. Some users pressed: with 6.1 million cells, is it running in real time, or was it simulated offline and then replayed? More than one person wanted to see frame times. Another user asked: did it work on the first try, or did it take fifty attempts to get it running? The author did not answer directly.

A user posted an image with no further explanation.

There was a small aside about “real-time.” A user, unconvinced, generated a campfire video with another AI model, Grok, claiming it was more realistic. Mark replied: That's a video, not real-time rendering.

The truly noteworthy information was hidden in one reply. A user asked: Compared with the final footage, I'm more interested in an editable scene. Can the camera be moved without rerunning the simulation? Mark replied only: Sure.

A year ago, demos of AI writing code were still at the Flappy Bird level. A year later, people are already discussing whether the camera can be dragged in a 6.1-million-cell physics simulation. A user joked with Red Dead Redemption 2's horse manure physics: Red Dead 3 will have this, and the future benchmark will be FPS plus multiple campfires. It's not entirely a joke.