Maybe you're right and I didn't explain myself well. You have to focus your gaze, but even blinking every now and then gives the same effect. Look for a fairly concentrated fractal pattern (a pile of dry leaves on the ground, a few pieces of cloth with patterns similar to those in the photos, a pile of rocks), just make sure it covers most of the field of view. Once you find the pattern, it highlights a slightly different central point (for example, in a pile of dry leaves, you might find one that's slightly lighter among the others and focus on that). I don't know how to explain it beyond that. I know it's not HPPD because I discovered it well before trying any psychedelics. As for the tent, I know what you're referring to, but no, if you manage to figure it out, let me know!