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fix: road mesh breaks on steep slope (Lombard) — faceting + buildings float over gaps #219

Description

@nigel-hall-codes

Problem

Roads and building placement break on steep grades. On flat ground (e.g. the foreground intersection) everything renders correctly, but on steep San Francisco hills (Lombard / Russian Hill) the geometry degrades badly.

Observed in screenshot badroadlombard.png.

Specific location

  • Chunk: chunk_27_35
  • Road: road_1252260414
  • Connecting intersection: 1580517057

Symptoms

  1. Road ribbon facets / zig-zags up the grade instead of conforming smoothly to the heightfield. Triangulation artifacts and pinching visible as the carriageway climbs.
  2. Buildings float / Z-fight on the slope — black gaps/slivers beneath footprints where foundations aren't clamped to sloped terrain.
  3. Terrain seams tear along road edges on the hill — road carriageway and heightfield don't share edges, producing a broken silhouette.

Suspected area

Road mesh generation + building base-snapping vs. the shared HeightField sampling on steep slopes. Flat-ground path is fine; steep-grade path is not. Likely culprits: ChunkStreamer, HeightField, road/building mesh emit.

Next

Investigate whether roads and building footprints are baked against the same HeightField sampling, and how the road ribbon is tessellated across steep grade.

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