OsmBuildingsTile

Renders every building of one slippy-map tile as a single batched mesh — one VBO + one EBO per tile per Globe.State, regardless of building count. Drop-in replacement for the legacy "one earth.worldwind.shape.Polygon per building" path that OOMs the Adreno KGSL shared-memory pool on dense urban tiles (~500 buildings × 4 buffers × ≥1-page mmap exhausts the kernel's GPU buffer-object slots by count long before raw bytes become a concern). Per-tile batching is the approach Cesium 3D Tiles b3dm, Mapbox fill-extrusion, and deck.gl SolidPolygonLayer all use for the same reason.

Per-building wall / roof colour (useOsmColors) is supported by grouping triangles within the tile's element array by colour and issuing one DrawShapeState.drawElements call per colour. Same one-VBO-one-EBO footprint; just more sub-draw calls per tile. A uniform-colour tile (the default) collapses to a single sub-draw.

Geometry per building follows the OSM "Simple 3D Buildings" convention:

• Top cap: flat horizontal slab tessellated via GLU (with holes from inner rings) at max(corner ground) + height so the roof clears every footprint corner.

• Side walls: each edge gets four fresh corner vertices (no sharing across walls or with the cap) so the fragment shader's dFdx-derived flat normal stays sharp at every face break. Ground-rooted walls drape their base to per-corner local terrain — the wall meets the ground at each corner regardless of slope.

• Bottom cap: only when OsmBuilding.minHeight> 0 (floating slab — bridges, podiums). For floating buildings the wall base is also planar at max(corner ground) + minHeight so the slab stays coplanar with the floor cap.

Per-building picking: in pick mode each OsmBuilding gets its own pick id and one DrawShapeState.drawElements sub-draw. A separate building-major element buffer (TileData.pickElementArray) backs this; the visual EBO stays colour-major. Click hits resolve to the OsmBuilding via PickedObject.userObject.