Cell the water falls FROM (the lip).
Edge index (0–5) the river leaves through — the cliff edge.
row * map.width + col of the lip cell — the fog-of-war cell index.
Cell index of the cell the water lands in (the lip's downstream neighbor).
World-space point where the sheet lands, centered across the channel.
World Y of the cliff lip — the channel surface the sheet leaves from.
Sheet width at the base, world units.
Vertical drop, world units (topY - baseY); always ≥ cliffThreshold × elevationScale.
Unit XZ flow direction, lip → base.
Accumulated flow at the lip cell (≥ 1); 1 when no flow map was supplied.
One rendered waterfall: the cliff edge a river channel pours over, resolved to the world-space anchor its spray and plunge pool are built around.
Produced by findWaterfalls, which mirrors the waterfall branch of
buildRiverGeometryexactly — including the terrain-matched vertex perturbation — so the base point really is where the falling sheet lands.