#151Page Turn / Card Flip

A warm sunset postcard (sourceA) peels off a cylinder like a turning page, revealing a cool neon ocean-grid (sourceB) underneath. A crease line sweeps right-to-left; within the curl band screen position maps back to arc angle so the paper foreshortens toward the fold, cos(theta) shades the near face into the terminator, and past the top of the fold the desaturated backside catches a bright rim highlight. A soft contact shadow falls on the freshly-exposed B just past the crease. The turn eases there-and-back so it loops forever with no pointer.