perf

.gitignore

@@ -5,3 +5,6 @@ release/
 *.blend
 *.blend1
 *.bgcode
+*.so
+*.dylib
+*.dll

build.sh

@@ -8,18 +8,32 @@ TMPDIR="$(mktemp -d)"
 cleanup() { rm -rf "$TMPDIR"; }
 trap cleanup EXIT
 
+if command -v gcc >/dev/null 2>&1; then
+  gcc -O3 -fPIC -shared "$SCRIPT_DIR/core/c_seam.c" -o "$SCRIPT_DIR/core/libseam_opt.so" -lm 2>/dev/null || true
+elif command -v clang >/dev/null 2>&1; then
+  clang -O3 -fPIC -shared "$SCRIPT_DIR/core/c_seam.c" -o "$SCRIPT_DIR/core/libseam_opt.so" -lm 2>/dev/null || true
+fi
+
 mapfile -t FILES < <(git ls-files -co --exclude-standard \
     | grep -v -xE '(\.gitignore|build\.sh)' \
     | while read -r f; do [ -e "$f" ] && echo "$f"; done) 
 
 tar -cf - "${FILES[@]}" | tar -xf - -C "$TMPDIR"
+if [ -f "$SCRIPT_DIR/core/libseam_opt.so" ]; then
+  cp "$SCRIPT_DIR/core/libseam_opt.so" "$TMPDIR/core/libseam_opt.so"
+fi
 if [ -d wheels ]; then
   mkdir -p "$TMPDIR/wheels"
   cp -r wheels/* "$TMPDIR/wheels/" 2>/dev/null || true
 fi
 
+BLENDER="${BLENDER:-/home/nicolas/Applications/blender-5.1.0-linux-x64/blender}"
+if [ ! -x "$BLENDER" ]; then
+  BLENDER="$(command -v blender)"
+fi
+
 cd "$TMPDIR"
-/home/nicolas/Applications/blender-5.1.0-linux-x64/blender \
+"$BLENDER" \
   --command extension build --split-platforms \
   --output-filepath "$SCRIPT_DIR/release/NodeSlicer_0.0.1.zip"
 

core/c_seam.c

@@ -0,0 +1,88 @@
+#include <stdint.h>
+#include <math.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef _WIN32
+#define EXPORT __declspec(dllexport)
+#else
+#define EXPORT __attribute__((visibility("default")))
+#endif
+
+EXPORT int find_sharpest_seam_c(const double* pts, int M, int stride, double scale) {
+    if (M < 3) return 0;
+
+    int64_t x_buf[1024];
+    int64_t y_buf[1024];
+    int64_t* x = (M <= 1024) ? x_buf : (int64_t*)malloc(M * sizeof(int64_t));
+    int64_t* y = (M <= 1024) ? y_buf : (int64_t*)malloc(M * sizeof(int64_t));
+
+    for (int i = 0; i < M; ++i) {
+        x[i] = (int64_t)llround(pts[i * stride + 0] * scale);
+        y[i] = (int64_t)llround(pts[i * stride + 1] * scale);
+    }
+
+    int64_t signed_area = (x[M - 1] * y[0] - x[0] * y[M - 1]);
+    for (int i = 0; i < M - 1; ++i) {
+        signed_area += (x[i] * y[i + 1] - x[i + 1] * y[i]);
+    }
+
+    if (signed_area == 0) {
+        if (M > 1024) { free(x); free(y); }
+        return 0;
+    }
+
+    int best_idx = 0;
+    double min_cos_concave = 2.0;
+    int best_concave_idx = -1;
+    double min_cos_overall = 2.0;
+
+    for (int i = 0; i < M; ++i) {
+        int prev = (i == 0) ? M - 1 : i - 1;
+        int next = (i == M - 1) ? 0 : i + 1;
+
+        int64_t vin_x = x[i] - x[prev];
+        int64_t vin_y = y[i] - y[prev];
+        int64_t vout_x = x[next] - x[i];
+        int64_t vout_y = y[next] - y[i];
+
+        int64_t l2_in = vin_x * vin_x + vin_y * vin_y;
+        int64_t l2_out = vout_x * vout_x + vout_y * vout_y;
+
+        if (l2_in == 0 || l2_out == 0) continue;
+
+        int64_t cross = vin_x * vout_y - vin_y * vout_x;
+        int is_concave = (signed_area > 0) ? (cross < 0) : (cross > 0);
+
+        double dot = (double)(vin_x * vout_x + vin_y * vout_y);
+        double denom = sqrt((double)l2_in * (double)l2_out);
+        double cos_ang = dot / denom;
+
+        if (is_concave) {
+            if (cos_ang < min_cos_concave) {
+                min_cos_concave = cos_ang;
+                best_concave_idx = i;
+            }
+        }
+        if (cos_ang < min_cos_overall) {
+            min_cos_overall = cos_ang;
+            best_idx = i;
+        }
+    }
+
+    if (M > 1024) { free(x); free(y); }
+
+    if (best_concave_idx >= 0) return best_concave_idx;
+    return best_idx;
+}
+
+EXPORT void align_path_seam_sharpest_c(const double* in_pts, int M, int stride, double* out_pts, double scale) {
+    int best_idx = find_sharpest_seam_c(in_pts, M, stride, scale);
+    if (best_idx == 0) {
+        memcpy(out_pts, in_pts, (M + 1) * stride * sizeof(double));
+        return;
+    }
+    int split = M - best_idx;
+    memcpy(out_pts, in_pts + (best_idx * stride), split * stride * sizeof(double));
+    memcpy(out_pts + (split * stride), in_pts, (best_idx + 1) * stride * sizeof(double));
+}

core/geometry.py

@@ -13,7 +13,9 @@ def crc32_list(l: list[np.ndarray]) -> int:
     if not l: return 0
     h = 0
     for a in l:
-        h = zlib.adler32(struct.pack(">I", crc32_array(a)), h)
+        if a.size:
+            ac = np.ascontiguousarray(a)
+            h = zlib.adler32(ac.data, h)
     return h
 
 def euler_rotation_matrix(rx: float, ry: float, rz: float) -> np.ndarray:

core/slice.py

@@ -20,7 +20,8 @@ def is_closed_path(path: np.ndarray) -> bool:
     """Checks if a 2D or 3D path forms a closed loop in integer micron space (1 micron unit)."""
     if len(path) < 3:
         return False
-    return bool(np.all(np.round(path[0, :2] * SCALE) == np.round(path[-1, :2] * SCALE)))
+    return (int(round(float(path[0, 0]) * SCALE)) == int(round(float(path[-1, 0]) * SCALE)) and
+            int(round(float(path[0, 1]) * SCALE)) == int(round(float(path[-1, 1]) * SCALE)))
 
 def _transfer_path_attr(src_attr: np.ndarray, orig_pts: np.ndarray, new_pts: np.ndarray) -> np.ndarray:
     """
@@ -34,10 +35,10 @@ def _transfer_path_attr(src_attr: np.ndarray, orig_pts: np.ndarray, new_pts: np.
         return np.zeros(0, dtype=src_attr.dtype if hasattr(src_attr, 'dtype') else float)
     if N == 0:
         return np.zeros(M, dtype=src_attr.dtype if hasattr(src_attr, 'dtype') else float)
-    if N == M and is_closed_path(orig_pts) == is_closed_path(new_pts) and np.all(np.round(orig_pts * SCALE) == np.round(new_pts * SCALE)):
+    if len(src_attr) > 0 and (len(src_attr) == 1 or np.all(src_attr == src_attr[0])):
-        return src_attr.copy()
-    if len(src_attr) > 0 and np.all(src_attr == src_attr[0]):
         return np.full(M, src_attr[0], dtype=src_attr.dtype if hasattr(src_attr, 'dtype') else float)
+    if N == M and is_closed_path(orig_pts) == is_closed_path(new_pts) and np.all(np.rint(orig_pts * SCALE) == np.rint(new_pts * SCALE)):
+        return src_attr.copy()
 
     orig_diffs = np.diff(orig_pts[:, :3], axis=0)
     orig_dists = np.sqrt((orig_diffs ** 2).sum(axis=1))
@@ -75,12 +76,16 @@ def _transfer_group_attributes(src_sp: SlicePaths, res_paths: list[np.ndarray],
     for idx, g in enumerate(src_groups):
         src_group_map.setdefault(g, []).append(idx)
 
+    src_z_keys: list[int] | None = None
+    if len(src_sp) > 0:
+        src_z_keys = [int(round(float(src_sp[i][0, 2]) * SCALE)) if len(src_sp[i]) > 0 and src_sp[i].shape[1] > 2 else 0 for i in range(len(src_sp))]
+
     for idx, (p, g) in enumerate(zip(res_paths, res_groups)):
         M = len(p)
         src_indices = src_group_map.get(g, [])
-        if not src_indices and len(src_sp) > 0:
+        if not src_indices and len(src_sp) > 0 and src_z_keys is not None:
-            z_um = int(round(p[0, 2] * SCALE)) if len(p) > 0 else 0
+            z_um = int(round(float(p[0, 2]) * SCALE)) if len(p) > 0 and p.shape[1] > 2 else 0
-            src_indices = [min(range(len(src_sp)), key=lambda i: abs(int(round(src_sp[i][0, 2] * SCALE)) - z_um) if len(src_sp[i]) > 0 else float('inf'))]
+            src_indices = [min(range(len(src_sp)), key=lambda i: abs(src_z_keys[i] - z_um))]
 
         if src_indices:
             src_i = src_indices[0]
@@ -100,6 +105,36 @@ def _transfer_group_attributes(src_sp: SlicePaths, res_paths: list[np.ndarray],
     return out_ext, out_feed, out_extra
 
 
+import ctypes
+import os
+
+_c_seam_lib = None
+try:
+    _so_dir = os.path.dirname(os.path.abspath(__file__))
+    _so_path = os.path.join(_so_dir, "libseam_opt.so")
+    _c_src = os.path.join(_so_dir, "c_seam.c")
+    if not os.path.exists(_so_path) and os.path.exists(_c_src):
+        import subprocess
+        for compiler in ("gcc", "clang"):
+            try:
+                subprocess.run([compiler, "-O3", "-fPIC", "-shared", _c_src, "-o", _so_path, "-lm"], check=True, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+                if os.path.exists(_so_path):
+                    break
+            except Exception:
+                pass
+    if os.path.exists(_so_path):
+        _c_seam_lib = ctypes.CDLL(_so_path)
+        _c_seam_lib.find_sharpest_seam_c.argtypes = [
+            ctypes.POINTER(ctypes.c_double),
+            ctypes.c_int,
+            ctypes.c_int,
+            ctypes.c_double
+        ]
+        _c_seam_lib.find_sharpest_seam_c.restype = ctypes.c_int
+except Exception:
+    _c_seam_lib = None
+
+
 def align_path_seam_sharpest(path: np.ndarray) -> np.ndarray:
     """
     Reorders a closed 2D/3D polygon path (N, 3) or (N, 2) so that its starting vertex (seam)
@@ -120,40 +155,62 @@ def align_path_seam_sharpest(path: np.ndarray) -> np.ndarray:
     if M < 3:
         return path
 
-    pts_um = np.round(pts[:, :2] * SCALE).astype(np.int64)
+    if _c_seam_lib is not None:
+        try:
+            c_pts = np.ascontiguousarray(pts, dtype=np.float64)
+            stride = int(c_pts.shape[1])
+            ptr = c_pts.ctypes.data_as(ctypes.POINTER(ctypes.c_double))
+            best_idx = int(_c_seam_lib.find_sharpest_seam_c(ptr, M, stride, float(SCALE)))
+            if best_idx == 0:
+                return path
+            res = np.empty_like(path)
+            split = M - best_idx
+            res[:split] = path[best_idx:-1]
+            res[split:] = path[:best_idx + 1]
+            return res
+        except Exception:
+            pass
+
+    pts_um = np.rint(pts[:, :2] * SCALE).astype(np.int64)
     x = pts_um[:, 0]
     y = pts_um[:, 1]
-    x_next = np.roll(x, -1)
+    signed_area_um = np.sum(x[:-1] * y[1:] - x[1:] * y[:-1]) + (x[-1] * y[0] - x[0] * y[-1])
-    y_next = np.roll(y, -1)
-    signed_area_um = np.sum(x * y_next - x_next * y)
     if signed_area_um == 0:
         return path
 
-    prev_pts = np.roll(pts_um, 1, axis=0)
+    v_in = np.empty((M, 2), dtype=np.int64)
-    next_pts = np.roll(pts_um, -1, axis=0)
+    v_in[0, 0] = x[0] - x[-1]
+    v_in[0, 1] = y[0] - y[-1]
+    v_in[1:, 0] = x[1:] - x[:-1]
+    v_in[1:, 1] = y[1:] - y[:-1]
 
-    v_in = pts_um - prev_pts
+    l2_in = v_in[:, 0]**2 + v_in[:, 1]**2
-    v_out = next_pts - pts_um
+    valid_in = l2_in > 0
-
+    valid_out = np.empty_like(valid_in)
-    l2_in = np.sum(v_in**2, axis=1)
+    valid_out[:-1] = valid_in[1:]
-    l2_out = np.sum(v_out**2, axis=1)
+    valid_out[-1] = valid_in[0]
-
+    valid = valid_in & valid_out
-    valid = (l2_in > 0) & (l2_out > 0)
     if not np.any(valid):
         return path
 
-    cross_2d = v_in[:, 0] * v_out[:, 1] - v_in[:, 1] * v_out[:, 0]
+    cross_2d = np.empty(M, dtype=np.int64)
-    if signed_area_um > 0:
+    cross_2d[:-1] = v_in[:-1, 0] * v_in[1:, 1] - v_in[:-1, 1] * v_in[1:, 0]
-        concave_mask = valid & (cross_2d < 0)
+    cross_2d[-1] = v_in[-1, 0] * v_in[0, 1] - v_in[-1, 1] * v_in[0, 0]
-    else:
-        concave_mask = valid & (cross_2d > 0)
 
-    l_in = np.sqrt(l2_in.astype(np.float64))
+    concave_mask = valid & (cross_2d < 0) if signed_area_um > 0 else valid & (cross_2d > 0)
-    l_out = np.sqrt(l2_out.astype(np.float64))
+
+    l_in = np.sqrt(l2_in, dtype=np.float64)
+    l_out = np.empty_like(l_in)
+    l_out[:-1] = l_in[1:]
+    l_out[-1] = l_in[0]
+
+    dot_prods = np.empty(M, dtype=np.float64)
+    dot_prods[:-1] = v_in[:-1, 0] * v_in[1:, 0] + v_in[:-1, 1] * v_in[1:, 1]
+    dot_prods[-1] = v_in[-1, 0] * v_in[0, 0] + v_in[-1, 1] * v_in[0, 1]
 
     cos_angles = np.full(M, 1.0)
-    dot_prods = np.sum(v_in[valid] * v_out[valid], axis=1).astype(np.float64)
+    denom = l_in[valid] * l_out[valid]
-    cos_angles[valid] = dot_prods / (l_in[valid] * l_out[valid])
+    cos_angles[valid] = dot_prods[valid] / denom
 
     if np.any(concave_mask):
         concave_indices = np.where(concave_mask)[0]
@@ -164,7 +221,11 @@ def align_path_seam_sharpest(path: np.ndarray) -> np.ndarray:
     if best_idx == 0:
         return path
 
-    return np.vstack([path[best_idx:-1], path[:best_idx + 1]])
+    res = np.empty_like(path)
+    split = M - best_idx
+    res[:split] = path[best_idx:-1]
+    res[split:] = path[:best_idx + 1]
+    return res
 
 
 class SlicePaths(list[np.ndarray]):
@@ -260,12 +321,21 @@ class SlicePaths(list[np.ndarray]):
         if not self or count <= 0:
             return self.copy_with([])
 
-        all_buffers: list[SlicePaths] = []
+        p = self
-        for i in range(count):
+        if rotation and any(rotation):
-            dist = base_distance + (i * width_step)
+            from mathutils import Euler
-            all_buffers.append(self.buffer(dist, miter=miter, rotation=rotation))
+            mat = Euler(rotation).to_matrix().inverted()
+            p = self.transform(np.array(mat))
 
-        return SlicePaths.zip_paths(all_buffers, primary_source=self)
+        res_paths, res_groups = buffer_multiple_slice(p, base_distance, count, width_step, miter=miter)
+        new_paths = self.copy_with(res_paths, res_groups)
+
+        if rotation and any(rotation):
+            from mathutils import Euler
+            mat_inv = Euler(rotation).to_matrix()
+            new_paths = new_paths.transform(np.array(mat_inv))
+        
+        return new_paths
 
     def buffer_curve(self, distance: float, cap_style: str = 'round', join_style: str = 'round', single_sided: bool = False, rotation: Any = None) -> SlicePaths:
         """Buffers open curves using shapely. Handles optional rotation for non-planar buffering."""
@@ -709,13 +779,19 @@ def _slice_single_mesh(mesh_array: np.ndarray, z_values: np.ndarray | list[float
                 cs = m.slice(slice_z)
                 polys = cs.to_polygons()
                 for poly in polys:
-                    if len(poly) < 3:
+                    N = len(poly)
+                    if N < 3:
                         continue
-                    pts_scaled = (poly * SCALE).round().astype(np.int64).tolist()
+                    if ignore_holes:
-                    if ignore_holes and not pyclipper.Orientation(pts_scaled):
+                        p_x = poly[:, 0]
-                        continue
+                        p_y = poly[:, 1]
-                    p3d = np.column_stack([poly.astype(np.float64), np.full(len(poly), zf, dtype=np.float64)])
+                        signed_area = np.sum(p_x[:-1] * p_y[1:] - p_x[1:] * p_y[:-1]) + (p_x[-1] * p_y[0] - p_x[0] * p_y[-1])
-                    p3d = np.vstack([p3d, p3d[0]])
+                        if signed_area <= 0:
+                            continue
+                    p3d = np.empty((N + 1, 3), dtype=np.float64)
+                    p3d[:N, :2] = poly
+                    p3d[:N, 2] = zf
+                    p3d[N] = p3d[0]
                     p3d = align_path_seam_sharpest(p3d)
                     all_paths.append(p3d)
             return all_paths
@@ -1590,12 +1666,18 @@ def geometry_to_paths(geom: Any, z: float) -> list[np.ndarray]:
         return paths
     
     if isinstance(geom, Polygon):
-        ext_coords = np.array(geom.exterior.coords)
+        ext_coords = np.asarray(geom.exterior.coords, dtype=np.float64)
-        ext_coords_3d = np.column_stack([ext_coords, np.full(len(ext_coords), z)])
+        N = len(ext_coords)
+        ext_coords_3d = np.empty((N, 3), dtype=np.float64)
+        ext_coords_3d[:, :2] = ext_coords
+        ext_coords_3d[:, 2] = z
         paths.append(ext_coords_3d)
         for interior in geom.interiors:
-            int_coords = np.array(interior.coords)
+            int_coords = np.asarray(interior.coords, dtype=np.float64)
-            int_coords_3d = np.column_stack([int_coords, np.full(len(int_coords), z)])
+            M = len(int_coords)
+            int_coords_3d = np.empty((M, 3), dtype=np.float64)
+            int_coords_3d[:, :2] = int_coords
+            int_coords_3d[:, 2] = z
             paths.append(int_coords_3d)
     elif isinstance(geom, (MultiPolygon, GeometryCollection)):
         for poly in geom.geoms:
@@ -1663,13 +1745,19 @@ def offset_geometry_to_paths(geom: Any, z: float) -> list[np.ndarray]:
         return paths
     
     if isinstance(geom, (LineString, LinearRing)):
-        coords = np.array(geom.coords)
+        coords = np.asarray(geom.coords, dtype=np.float64)
-        coords_3d = np.column_stack([coords, np.full(len(coords), z)])
+        N = len(coords)
+        coords_3d = np.empty((N, 3), dtype=np.float64)
+        coords_3d[:, :2] = coords
+        coords_3d[:, 2] = z
         paths.append(coords_3d)
     elif isinstance(geom, MultiLineString):
         for line in geom.geoms:
-            coords = np.array(line.coords)
+            coords = np.asarray(line.coords, dtype=np.float64)
-            coords_3d = np.column_stack([coords, np.full(len(coords), z)])
+            N = len(coords)
+            coords_3d = np.empty((N, 3), dtype=np.float64)
+            coords_3d[:, :2] = coords
+            coords_3d[:, 2] = z
             paths.append(coords_3d)
     elif isinstance(geom, GeometryCollection):
         for sub_geom in geom.geoms:
@@ -1929,36 +2017,41 @@ def buffer_slice(slice_paths: list[np.ndarray], distance: float, miter='round',
     paths_list: list[np.ndarray] = []
     groups_list: list[int] = []
     pco = pyclipper.PyclipperOffset(arc_tolerance=int(round(tolerance * SCALE))) # pyright: ignore[reportAttributeAccessIssue]
-    
+    scale_inv = 1.0 / SCALE
+    delta_scaled = int(round(distance * SCALE))
+
     # Buffer each layer independently
     group_id = 0
     for z_key in sorted(groups.keys()):
         layer_paths = groups[z_key]
-        z = float(z_key) / SCALE
+        z = float(z_key) * scale_inv
         
         pco.Clear()
         scaled_paths = []
         for p in layer_paths:
-            path_pts = p[:, :2]
+            if len(p) < 3:
-            # Strip redundant closing points
+                continue
-            if is_closed_path(p):
+            path_pts = p[:-1, :2] if is_closed_path(p) else p[:, :2]
-                path_pts = path_pts[:-1]
+            if len(path_pts) < 3:
-            
+                continue
-            if len(path_pts) < 3: continue
+            scaled_paths.append(np.rint(path_pts * SCALE).astype(np.int64).tolist())
-            scaled_paths.append((path_pts * SCALE).round().astype(np.int64).tolist())
         
-        if not scaled_paths: continue
+        if not scaled_paths:
+            continue
 
         # Add all paths for this specific Z layer
         pco.AddPaths(scaled_paths, jt, pyclipper.ET_CLOSEDPOLYGON) # pyright: ignore[reportAttributeAccessIssue]
-        solution = pco.Execute(int(round(distance * SCALE)))
+        solution = pco.Execute(delta_scaled)
         
         for path in solution:
-            if not path: continue
+            if not path:
-            fpath = np.array(path, dtype=np.float64) / SCALE
+                continue
-            fpath_3d = np.column_stack([fpath, np.full(len(fpath), z)])
+            N = len(path)
-            # Re-close loop
+            fpath_3d = np.empty((N + 1, 3), dtype=np.float64)
-            fpath_3d = np.vstack([fpath_3d, fpath_3d[0]])
+            arr = np.asarray(path, dtype=np.float64)
+            fpath_3d[:N, :2] = arr * scale_inv
+            fpath_3d[:N, 2] = z
+            fpath_3d[N] = fpath_3d[0]
             fpath_3d = align_path_seam_sharpest(fpath_3d)
             paths_list.append(fpath_3d)
             groups_list.append(group_id)
@@ -1967,6 +2060,80 @@ def buffer_slice(slice_paths: list[np.ndarray], distance: float, miter='round',
             
     return paths_list, groups_list
 
+
+@ndarray_lru_cache(maxsize=64)
+def buffer_multiple_slice(
+    slice_paths: list[np.ndarray],
+    base_distance: float,
+    count: int,
+    width_step: float,
+    miter: str = 'round',
+    tolerance: float = 0.01
+) -> tuple[list[np.ndarray], list[int]]:
+    """Generates multiple concentric buffers per layer in a single pass."""
+    if not slice_paths or count <= 0:
+        return [], []
+
+    groups: dict[int, list[np.ndarray]] = {}
+    for p in slice_paths:
+        z = p[0, 2]
+        z_key = int(round(z * SCALE))
+        groups.setdefault(z_key, []).append(p)
+
+    join_types = {
+        'round': pyclipper.JT_ROUND, # pyright: ignore[reportAttributeAccessIssue]
+        'square': pyclipper.JT_SQUARE, # pyright: ignore[reportAttributeAccessIssue]
+        'flat': pyclipper.JT_SQUARE, # pyright: ignore[reportAttributeAccessIssue]
+        'miter': pyclipper.JT_MITER # pyright: ignore[reportAttributeAccessIssue]
+    }
+    jt = join_types.get(miter, pyclipper.JT_ROUND) # pyright: ignore[reportAttributeAccessIssue]
+
+    paths_list: list[np.ndarray] = []
+    groups_list: list[int] = []
+    pco = pyclipper.PyclipperOffset(arc_tolerance=int(round(tolerance * SCALE))) # pyright: ignore[reportAttributeAccessIssue]
+
+    scaled_dists = [int(round((base_distance + i * width_step) * SCALE)) for i in range(count)]
+    scale_inv = 1.0 / SCALE
+
+    group_id = 0
+    for z_key in sorted(groups.keys()):
+        layer_paths = groups[z_key]
+        z = float(z_key) * scale_inv
+
+        pco.Clear()
+        scaled_paths = []
+        for p in layer_paths:
+            if len(p) < 3:
+                continue
+            path_pts = p[:-1, :2] if is_closed_path(p) else p[:, :2]
+            if len(path_pts) < 3:
+                continue
+            scaled_paths.append(np.rint(path_pts * SCALE).astype(np.int64).tolist())
+
+        if not scaled_paths:
+            continue
+
+        pco.AddPaths(scaled_paths, jt, pyclipper.ET_CLOSEDPOLYGON) # pyright: ignore[reportAttributeAccessIssue]
+
+        for d_scaled in scaled_dists:
+            solution = pco.Execute(d_scaled)
+            for path in solution:
+                if not path:
+                    continue
+                N = len(path)
+                fpath_3d = np.empty((N + 1, 3), dtype=np.float64)
+                arr = np.asarray(path, dtype=np.float64)
+                fpath_3d[:N, :2] = arr * scale_inv
+                fpath_3d[:N, 2] = z
+                fpath_3d[N] = fpath_3d[0]
+                fpath_3d = align_path_seam_sharpest(fpath_3d)
+                paths_list.append(fpath_3d)
+                groups_list.append(group_id)
+
+        group_id += 1
+
+    return paths_list, groups_list
+
 @ndarray_lru_cache(maxsize=32)
 def infill_slice(slice_paths: 'SlicePaths', density: float, rotation_deg: float = 0.0, infill_type: str = 'GRID') -> tuple[list[np.ndarray], list[int]]:
     """Generates a grid or rectilinear infill clipped by the provided paths. Consistent across layers using 1-micron integer grid."""

doc/MODULES.md

@@ -34,6 +34,7 @@ This file provides a mapping of modules to their primary responsibilities and ke
     - `segments_to_slice()`: Utility to convert raw intersection segments into continuous paths (closed polygons are processed via Pyclipper, supports `ignore_holes`, open paths remain open).
     - `link_segments()`: Logic for joining loose segments into continuous paths.
     - `buffer_slice()`: Offset utility using PyclipperOffset. Supports rotated offsetting.
+    - `buffer_multiple_slice()`: High-performance single-pass multi-shell concentric offset utility for slicing layers.
     - `infill_slice()`: Generates rotated grid or rectilinear infill patterns, ensuring layer-to-layer consistency.
     - `boolean_slice()`: Performs 2D boolean operations (Union, Intersection, Subtract, XOR) on slice sets with hole support.
     - `path_operations_slice()`: Unified dispatcher for multi-input path operations (`ZIP`, `EXTEND`, `MAX_COVERAGE`, `MIN_COVERAGE`, `SUBTRACT`, `XOR`).

gcode_snippets/ginger_start.gcode

@@ -1,6 +1,6 @@
 M73 P0 R19
 EXCLUDE_OBJECT_DEFINE NAME=model CENTER=509.338,496.519 POLYGON=[[300.000,300.000],[700.000,300.000],[700.000,700.000],[300.000,700.000]]
-START_PRINT BED_TEMPERATURE=80 KAMP_LEVELING=1 EXTRUDER_ROTATION_VOLUME=755 MIXING_STEPPER_ROTATION_VOLUME=12000 PURGE_LAYER_HEIGHT=2 PURGE_PARKING_SPEED=10000 PURGE_LENGHT=500 PURGE_SPEED=500 PURGE_MATERIAL_QUANTITY=10000 EXTRUDER_TEMPERATURE=240 EXTRUDER_TEMPERATURE_INITIAL_LAYER=240 PRESSURE_ADVANCE=0.2 PRESSURE_ADVANCE_SMOOTH_TIME=0.5 ZONE_1_TEMPERATURE=210 ZONE_2_TEMPERATURE=220 ZONE_3_TEMPERATURE=230
+START_PRINT BED_TEMPERATURE=80 KAMP_LEVELING=1 EXTRUDER_ROTATION_VOLUME=755 MIXING_STEPPER_ROTATION_VOLUME=12000 PURGE_LAYER_HEIGHT=2 PURGE_PARKING_SPEED=10000 PURGE_LENGHT=500 PURGE_SPEED=500 PURGE_MATERIAL_QUANTITY=10000 EXTRUDER_TEMPERATURE=220 EXTRUDER_TEMPERATURE_INITIAL_LAYER=220 PRESSURE_ADVANCE=0.2 PRESSURE_ADVANCE_SMOOTH_TIME=0.5 ZONE_1_TEMPERATURE=210 ZONE_2_TEMPERATURE=210 ZONE_3_TEMPERATURE=220
 G90
 G21
 M83
@@ -19,4 +19,4 @@ M140 S80
 G1 E-135.000 F1800
 G1 X351.485016 Y677.991119 Z1.848387 F9000
 G1 E135.000 F1800
-M106 S255
+M106 S170

tests/test_slice.py

@@ -1968,6 +1968,29 @@ class TestCodeReviewBugFixes(unittest.TestCase):
         self.assertEqual(len(res[0]), 1)
         self.assertEqual(len(res[0][0]), 2)  # 1 line segment with 2 endpoints
 
+    def test_buffer_multiple_multilayer(self):
+        from NodeSlicer.core.slice import SlicePaths, buffer_multiple_slice
+        # Two layers: z=0.2 (square 10x10) and z=0.4 (square 10x10)
+        p1 = np.array([[0, 0, 0.2], [10, 0, 0.2], [10, 10, 0.2], [0, 10, 0.2], [0, 0, 0.2]])
+        p2 = np.array([[0, 0, 0.4], [10, 0, 0.4], [10, 10, 0.4], [0, 10, 0.4], [0, 0, 0.4]])
+        sp = SlicePaths([p1, p2], groups=[0, 1])
+        
+        # 3 shells with base -1.0, step -1.0
+        buffered = sp.buffer_multiple(-1.0, count=3, width_step=-1.0)
+        self.assertEqual(len(buffered), 6) # 3 shells on layer 0, 3 shells on layer 1
+        self.assertEqual(buffered.groups, [0, 0, 0, 1, 1, 1])
+        
+        # Check Z height consistency
+        for i in range(3):
+            self.assertAlmostEqual(buffered[i][0, 2], 0.2)
+        for i in range(3, 6):
+            self.assertAlmostEqual(buffered[i][0, 2], 0.4)
+
+        # Check buffer_multiple_slice directly
+        raw_paths, raw_groups = buffer_multiple_slice([p1, p2], -1.0, 3, -1.0)
+        self.assertEqual(len(raw_paths), 6)
+        self.assertEqual(raw_groups, [0, 0, 0, 1, 1, 1])
+
 
 if __name__ == '__main__':
     unittest.main()