Here, that was an experiment to see the math involved in the Vertigo Effect, which consisted as zooming in a specific speed matching the panning you'd to keep your subject in the same size and position in your camera, but the world around them would dramatically shift in position.
Don't mind too much the rest of the scene, that's the rest of remnants of a failed OpenGL engine.
@hillexed if Wikipedia is referring me to the proper stuff, distance = width/(2 * tan(fov / 2))
It needed a vit of massaging to get into the code but once it was there, it worked neatly
the mastodon instance at cybre.space is retired
see the end-of-life plan for details: https://cybre.space/~chr/cybre-space-eol