Generates the raised sidewalk for a city's blocks: per block, a rounded-corner concrete
slab rimmed by a distinct granite kerbstone that stands proud of the walking surface and
drops to the road. Instanced across a list of placements and dressed with its own
procedural material ( poured concrete flags, scored expansion joints, granite curb ).
Returns a THREE.Group of two instanced meshes — the walking slab and the curb.
Unlike the building generator, this one owns its materials: the slab and curb geometry and the TSL that shades them live together here.
const sidewalk = new SidewalkGenerator( { width: 90, depth: 60, height: 0.5 } );
scene.add( sidewalk.build( placements ) ); // placements: Matrix4[]