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Hanif Koh
4e43ab8306
Painted (multi-material) models sliced to slightly different G-code on every run: ±1 µm wall coordinates and reordered islands. Hashing each stage of the segmentation across runs showed the projected painted lines and the per-layer Voronoi segmentation were stable; the raw top/bottom projections from slice_mesh_slabs() were not. Three causes, all thread-order dependent: - slice_slabs_make_lines() appends each slab's intersection lines from a parallel facet loop and never restored a canonical order, so the loop start vertices and polygon order from make_slab_loops() depended on scheduling. Sort every slab's lines with the same key slice_make_lines() already uses. - segmentation_top_and_bottom_layers() wrote a layer's shell projections into neighbouring layers' vectors from the parallel loop, relying on a parity double-buffer that assumes TBB ranges are exactly one group wide and aligned, which blocked_range does not guarantee; two threads could append to the same vector. Each source layer now records its projections in its own slot and they are gathered per target layer in source order. - The painted-line sort in post_process_painted_lines() was not a total order: projections of one span from facets of different colours tied on every key and the first one won the span. Colour and end points now break the tie. Three multi-threaded runs of each painted fixture now give one G-code; unpainted output is unchanged.