@ifc-lite/drawing-2d@1.18.4

Patch Changes

• #1311 207a4fb Thanks @louistrue! - Reconstruct per-layer section fills from open (cap-free) material-layer bands. The geometry slicer no longer caps the layer interface planes — capping doubled each shared interface into a coincident, non-watertight "ghost face" sheet and ~tripled the triangle count on layered walls. With the interfaces left open, the 2D section's polygon builder is now bidirectional (each open band closes at the interface chord) and, for 3+ layer walls, stitches the disconnected end strips of an interior layer (which has no wall face) back into a closed fill at the interface chords — so every layer keeps its section fill.

  Harden that reconstruction on OPENING-cut walls so the 3D section cap covers every layer (no more wall-reads-hollow in section view). An opening splits each layer into disconnected solid chunks; the old greedy nearest-endpoint stitch hopped an interior layer's strip to the strip ACROSS the opening, emitting one self-overlapping polygon that bridged the void and failed to fill. Closure now runs along the interface lines (the principal/length axis of the band, so it is robust to rotated walls): endpoints are paired CONSECUTIVELY along each interface line, which closes each solid chunk and leaves the opening between chunks empty. Ambiguous layouts fall back to the previous stitch, so no case is made worse.

  Add an opaque base-cap backstop so a 3D section cut can NEVER read see-through, even on a wall the per-layer reconstruction cannot resolve. For each multi-material entity the builder also emits its full closed cross-section (the watertight union of the bands always closes, so this needs no interface stitching), carried in a new Drawing2D.layerBaseCutPolygons that ONLY the 3D section overlay consumes (the flat 2D drawing, SVG export, and measure/snap paths are untouched). The overlay draws this opaque base first and the per-layer colours over it, so the colours show where they reconstruct and solid cut material shows everywhere else.

  Fix multilayer walls reading HOLLOW in normal (uncut) 3D, not just in section. The renderer backface-culled material-layer slices on the assumption their winding was reliably outward — correct for the OLD closed per-layer slabs (the cull hid their coincident interface caps). Since the slabs became open bands whose union is the wall's watertight outer skin (no caps), and IFC winding is not reliably outward, culling dropped inward-wound faces and punched holes, so the wall looked like a thin see-through shell. Layer slices now render DOUBLE-SIDED like all other IFC geometry: every face of the watertight skin draws, so the wall reads solid. With no coincident caps left there is nothing to z-fight, so the cull that motivated the special pipeline is removed (the GEOM_CLASS_LAYER_SLICE tag stays — it now only marks per-layer section fills).