nx_infill.nx

nx_infill.nx -- scan-line infill pattern generator for closed NxPolygon contours. Produces line segments that the G-code emitter prints as rectilinear infill inside the perimeter. Algorithm: classical scan-line fill (Foley/van Dam 1990). 1. compute polygon bbox 2. for each horizontal scan line at y = bbox.min_y + k*spacing: a. find x-coord where each polygon edge crosses y (skip horizontal edges; integer cross-multiply form) b. sort x-coords ascending c. pair consecutive crossings; emit segment per pair Spacing derived from line_width + density_pct: spacing_mm = (line_width_mm * 100) / density_pct Density 100% = touching lines, 50% = 50% air, 25% = 75% air. Grid pattern (perpendicular alternation per layer for better mechanical isotropy): when called with vertical=1, the algorithm runs on a transposed (x<->y) coordinate system, producing vertical scan lines. Caller toggles `vertical` per layer index. Reuses NxSliceSoup as output (same flat-segment shape as nx_slice_plane; downstream G-code emitter consumes either). Composes nx_polygon (closed contour input) + nx_qsort_i64 (crossing-coord sort) + nx_slice_plane (segment soup output type). Per cardinal NISHI_3D_PRINT_ROADMAP §2.x infill: lines pattern v1 is the substrate floor. Honeycomb / gyroid / cubic are future patterns queued for after this primitive validates on real prints. Per cardinal feedback-bits-up-exceed-never-match: substrate ships the universal scan-line core; richer patterns layer on top, NOT instead of, this primitive. Pure i64 arithmetic throughout (integer cross-multiply avoids division during the straddle test; one division per crossing for the x-coord computation). license_tier: ORIGINAL