nx_river_carve.nx

nx_river_carve.nx -- specialized river generator (NOT FBM noise). Second demonstration of the kind-specific-generator cardinal `feedback-kind-specific-generators-not-broad-noise`. Rivers have INTERNAL LOGIC -- meandering polyline paths, downstream widening, banks with depth ramp, river-stage sealed enum -- none of which is FBM noise. River-internal logic in v1: - Polyline path with N control points -- caller can pre-supply real-river data OR call nx_river_generate_path() to procgen a meandering sinuous line via hash-perturbed random walk. - 4 river types (HEADWATERS / MIDDLE / LOWER / DELTA) with characteristic width + bank profile + meander tightness. - Downstream widening: river gets wider as it flows (caller parameterises via per-segment width or uses the type-default). - Banks: linear ramp from full depth at channel axis to 0 at bank_width. Caller composes the carve depth into their base heightmap by subtraction. - Closest-point-on-polyline lookup -- iterates segments, finds min squared distance to any segment's line, returns the carve depth at that distance (parabolic falloff within the river + bank zone, 0 outside). FULL CAPABILITY (per feedback-maximum-capability-no-simplification cardinal, 2026-05-16): - True sin/cos meandering via nx_camera_sin/cos_q14_centideg (replaces 8-octant axis-aligned approximation; rivers now bend at arbitrary angles, not just multiples of 45°) - Oxbow lake detection + carving: scans for meander segments that loop back near themselves, marks the enclosed pinch-off as a stagnant water carve (no flow, full depth) - Delta braiding: for NX_RIVER_TYPE_DELTA paths, nx_river_generate_delta produces N branching channels fanning from the upstream point to spread-targets at the terminus Loss audit: Q14 integer arithmetic; squared-distance compare avoids sqrt for the per-pixel hot path. Hash-deterministic meander generation (Park-Miller LCG), no randomness leak. Genevaux 2013 drainage-graph integration NOT implemented here (the upgrade path