Basic World Window Controller
Properties
Inertial pan animator. Each platform's createFlingScheduler supplies the per-frame clock. The per-frame action dispatches by projection: 2D uses incremental projected-meters math, 3D uses great-circle radians. Picking the right one matters because Mercator metersPerPixel diverges from the 3D radians-on-a-sphere formula away from the equator.
Shared anchor for pinch / rotate / wheel handlers. Lazy because engine may not be initialized yet at controller-construction time.
Trailing-window velocity tracker used to seed fling on gesture release.
Functions
Cancels any in-progress inertial pan ("fling"). The host calls this on every press before routing the event downstream, so the user can abort the animation by clicking even when a select/drag detector or app listener consumes the press.