pyckingsolver

Shapely-based Python interface for PackingSolver — 2D irregular bin packing & nesting.

Pack irregular shapes into bins — rectangles, circles, arbitrary polygons with holes. Built for CNC laser cutting, sheet metal nesting, fabric cutting, and any 2D packing problem.

Laser cutting layout: mounting plates with bolt holes, washers, U-brackets, discs & gussets

Install

pip install pyckingsolver

The C++ solver binary is bundled — no compilation needed on Windows x64 and Linux x64.

For other platforms, build the solver from the included submodule. See Building the Solver.

What's New in 0.9.1

• C++ pin moves to packingsolver 816b70771 (master, 2026-10-05). Irregular's only change there remaps a sub-instance's fixed items before checking them. It does not fix the fixed-item reduction crash: an item type merged into an identical one still has no sub-instance id, so a pinned duplicate still throws "fixed item type id not found in sub-instance mapping". The 0.9.0 workaround stays: SolverParams.reduce=None means off when a bin has fixed items.
• Faster stall kills. The watchdog dates a new layout by the certificate's write instead of the poll that noticed it, and polls every 0.05 s instead of 0.25 s, so a stall-killed solve stops about 0.2 s sooner. Its timeouts still run on the monotonic clock.

Older release notes: CHANGELOG.md.

Gallery

Hole Fill	Custom Holes & Rings	Metal Cutting
Filler placed inside frame hole	Frames, rings, discs & triangles	Plates, washers, brackets & gussets

All Features — Example Results

#	Example	Preview
1	BIN_PACKING — fewest bins (rects, triangles, circles)
2	KNAPSACK — maximize profit
3	OPEN_DIMENSION_X — minimize strip width, free rotation
4	OPEN_DIMENSION_Y — minimize strip height
6	VARIABLE_SIZED_BIN_PACKING — multi-size bins, min cost
7	BIN_PACKING_WITH_LEFTOVERS — leftover tracking
8	DEFECTS — avoid scratch zones
9	POLYGON BIN — hexagonal bin
10	HOLES & MIRRORING — frames with holes, L-shapes
11	LP=Highs + ANCHOR — post-processing
12	JSON ROUND-TRIP — serialize → load → solve

Note: OPEN_DIMENSION_XY needs set_open_dimension_xy_aspect_ratio(...); without one the solver rejects the instance.

Quick Start

from shapely.geometry import Polygon, Point
from pyckingsolver import InstanceBuilder, Objective, Solver

b = InstanceBuilder(Objective.OPEN_DIMENSION_X)
b.add_bin_type_rectangle(1200, 600)
b.add_item_type_rectangle(80, 60, copies=10)
b.add_item_type(Polygon([(0,0),(50,0),(25,40)]), copies=6)

solver = Solver()  # auto-finds bundled binary
solution = solver.solve(b.build(), time_limit=30)

print(f"{solution.total_item_count()} items in {solution.total_bins_used()} bins")

for item in solution.all_items():
    print(item.item_type_id, item.angle, item.shapes[0].bounds)

Debugging against the C++ solver

Everything the wrapper exchanges with packingsolver_irregular is JSON, so any solve can be reproduced against the upstream binary by hand.

inst = builder.build()
inst.to_json("instance.json")             # byte-identical to what solve() sends

sol = Solver().solve(inst, json_output="certificate.json")   # the solver's own output, verbatim
sol.to_json("sparse.json")                # upstream's editable solution format

packingsolver_irregular --input instance.json --certificate out.json --output metrics.json

The two solution files are different on purpose:

Solution.metrics comes from the --output file, not the certificate.

Objectives

Choose what the solver optimizes:

All C++ naming conventions are accepted — kebab-case, PascalCase, and abbreviations:

Objective("bin-packing")             # kebab-case (canonical)
Objective("BinPacking")              # PascalCase
Objective("BPP")                     # abbreviation
Objective("BinPackingWithLeftovers")  # PascalCase
Objective("BPPL")                    # abbreviation

from pyckingsolver import Objective

b = InstanceBuilder(Objective.BIN_PACKING)

InstanceBuilder

Bins

b = InstanceBuilder(Objective.BIN_PACKING)

# Rectangle bin
b.add_bin_type_rectangle(1200, 600, copies=10, cost=1.0)

# Circle bin (discretized to a polygon — see Shape Format below)
b.add_bin_type_circle(radius=300)

# Any Shapely polygon
b.add_bin_type(Polygon([...]))

# With edge clearance (e.g. clamp margin)
b.add_bin_type_rectangle(1200, 600, item_bin_minimum_spacing=5.0)

# Multiple bin types (variable-sized bin packing)
small_id = b.add_bin_type_rectangle(600, 400, cost=1.0, copies=5)
large_id = b.add_bin_type_rectangle(1200, 800, cost=1.8, copies=3)

Items

# Rectangle item
b.add_item_type_rectangle(80, 60, copies=4)

# Any Shapely polygon
b.add_item_type(Polygon([(0,0),(100,0),(50,80)]), copies=6)

# Polygon with interior hole (e.g. washer, frame)
washer = Point(0,0).buffer(30).difference(Point(0,0).buffer(15))
b.add_item_type(washer, copies=4)

# With profit (for knapsack)
b.add_item_type(polygon, copies=3, profit=42.0)

# Multiple shapes per item (composite/multi-part item)
b.add_item_type([shape_a, shape_b], copies=2)

# Force at least N copies to be packed (KNAPSACK only — elsewhere every copy is mandatory)
b.add_item_type(polygon, copies=5, copies_min=2)

Rotations

The allowed_rotations parameter accepts several shapes — each entry maps to one upstream AllowedRotation { start_angle, end_angle, mirror } record:

from pyckingsolver import AllowedRotation

# Fixed at 0° (default if omitted)
b.add_item_type(shape)

# Discrete angles (mirror=False each)
b.add_item_type(shape, allowed_rotations=[0, 90, 180, 270])

# 2-tuples — continuous ranges, mirror=False
b.add_item_type(shape, allowed_rotations=[(0, 0), (90, 90)])

# 3-tuples — full triple form (start, end, mirror)
b.add_item_type(shape, allowed_rotations=[(0, 0, False), (90, 90, True)])

# Free continuous rotation
b.add_item_type(shape, allowed_rotations=[(0, 360)])

# AllowedRotation dataclass directly
b.add_item_type(shape, allowed_rotations=[AllowedRotation(0, 360, False),
                                          AllowedRotation(0, 360, True)])

# Back-compat: duplicate every entry with mirror=True
b.add_item_type(shape, allow_mirroring=True)

Fixed Items

Pre-place an item that the solver must pack around. Applies to every bin of the chosen BinType:

b = InstanceBuilder(Objective.BIN_PACKING)
bin_id  = b.add_bin_type_rectangle(1200, 600)
plate_id = b.add_item_type_rectangle(200, 100)        # "plate" item type
b.add_item_type_rectangle(80, 60, copies=20)          # parts to pack

# Lock one plate at (50, 50) on every bin of this type
b.add_fixed_item(bin_id, plate_id, (50, 50), angle=0, mirror=False)

solution = Solver().solve(b.build(), time_limit=30)

# Identify the locked items in the solution (set by the wrapper post-parse)
for it in solution.all_items():
    if it.is_fixed:
        print("locked at", it.x, it.y)

Caveat: the C++ solver's JSON output does not currently emit the is_fixed flag. The wrapper reconstructs it by matching each placement against the bin's fixed_items list (Solution.mark_fixed_items()).

Spacing

# Minimum gap between all items (e.g. 2mm laser kerf)
b.set_item_item_minimum_spacing(2.0)

# Clearance from bin edges (per bin type)
b.add_bin_type_rectangle(1200, 600, item_bin_minimum_spacing=5.0)

Defects

Defects are no-go zones inside a bin (scratches, holes, clamps):

bin_id = b.add_bin_type_rectangle(1200, 600)

# Add a defect (no item may overlap it)
scratch = Polygon([(100,100),(200,100),(200,150),(100,150)])
b.add_defect(bin_id, scratch)

# With clearance around defect
b.add_defect(bin_id, scratch, item_defect_minimum_spacing=3.0)

# With defect type label
b.add_defect(bin_id, scratch, defect_type=1)

Aspect Ratio (Open Dimension XY)

b = InstanceBuilder(Objective.OPEN_DIMENSION_XY)
b.set_open_dimension_xy_aspect_ratio(1.5)  # enforce width/height <= 1.5 (required)

Leftover Mode

For BIN_PACKING_WITH_LEFTOVERS, set the reference corner/edge for scrap:

from pyckingsolver import LeftoverMode

b.set_leftover_mode(LeftoverMode.BOTTOM_LEFT)   # default
b.set_leftover_mode(LeftoverMode.TOP_RIGHT)
b.set_leftover_mode(LeftoverMode.RIGHT)         # edge: full-height strip

Modes accept all C++ naming formats:

LeftoverMode("BottomLeft")    # PascalCase (canonical)
LeftoverMode("bl")            # abbreviation
LeftoverMode("bottom-left")   # kebab-case

Use Cases

Laser Cutting / Sheet Metal Nesting

Minimize material usage from a fixed sheet with kerf spacing:

from shapely.geometry import Polygon, Point
from pyckingsolver import InstanceBuilder, Objective, Solver

b = InstanceBuilder(Objective.BIN_PACKING)
b.set_item_item_minimum_spacing(2.0)        # 2mm laser kerf
b.add_bin_type_rectangle(1200, 600, copies=100)

# Mounting plate with bolt holes
plate = Polygon([(0,0),(150,0),(150,100),(0,100)])
for cx, cy in [(25,25),(125,25),(25,75),(125,75)]:
    plate = plate.difference(Point(cx,cy).buffer(12, resolution=16))
b.add_item_type(plate, copies=8,
                allowed_rotations=[(0,0),(90,90),(180,180),(270,270)])

# Discs that nest inside the bolt holes
b.add_item_type(Point(0,0).buffer(8, resolution=16), copies=16)

# L-bracket
b.add_item_type(
    Polygon([(0,0),(80,0),(80,60),(70,60),(70,10),(10,10),(10,60),(0,60)]),
    copies=12, allowed_rotations=[(0,0),(90,90),(180,180),(270,270)])

solution = Solver().solve(b.build(), time_limit=60)
print(f"{solution.total_item_count()} parts in {solution.total_bins_used()} sheets")

Roll / Strip Cutting

Minimize roll length consumed:

b = InstanceBuilder(Objective.OPEN_DIMENSION_X)
b.set_item_item_minimum_spacing(1.5)
b.add_bin_type_rectangle(99999, 1200)   # very long, fixed width

b.add_item_type(shape_a, copies=20, allowed_rotations=[(0, 360)])
b.add_item_type(shape_b, copies=15, allowed_rotations=[(0, 360)])

solution = Solver().solve(b.build(), time_limit=30)
used_length = max(item.x + item.shapes[0].bounds[2]
                  for item in solution.all_items())
print(f"Roll used: {used_length:.1f} mm")

Knapsack / Value Maximization

Pack as much value as possible in one bin:

b = InstanceBuilder(Objective.KNAPSACK)
b.add_bin_type_rectangle(500, 300)

shapes_with_values = [
    (Polygon([...]), 10.0),
    (Polygon([...]), 25.0),
]
for shape, profit in shapes_with_values:
    b.add_item_type(shape, copies=5, profit=profit)

solution = Solver().solve(b.build(), time_limit=30)
total_profit = sum(
    instance.item_types[item.item_type_id].profit
    for item in solution.all_items()
)

Variable-Sized Bin Packing

Choose from multiple sheet sizes to minimize cost:

b = InstanceBuilder(Objective.VARIABLE_SIZED_BIN_PACKING)
b.add_bin_type_rectangle(600, 400, cost=1.0, copies=10)
b.add_bin_type_rectangle(1200, 800, cost=1.8, copies=5)

for shape in my_parts:
    b.add_item_type(shape, copies=2)

solution = Solver().solve(b.build(), time_limit=60)

Defective Sheet Handling

Avoid defective zones on material:

b = InstanceBuilder(Objective.BIN_PACKING)
bin_id = b.add_bin_type_rectangle(1200, 600)

# Scratch at center — no item within 3mm
scratch = Point(600,300).buffer(40)
b.add_defect(bin_id, scratch, item_defect_minimum_spacing=3.0)

# Clamped edges — keep items 10mm from edges
b.add_bin_type_rectangle(1200, 600, item_bin_minimum_spacing=10.0)

Arbitrary Polygon Bins

Non-rectangular cutting areas (e.g., round table, irregular offcut):

# Circular bin
b.add_bin_type_circle(radius=500)

# Hexagonal bin
import math
hex_pts = [(500*math.cos(math.pi/3*i), 500*math.sin(math.pi/3*i)) for i in range(6)]
b.add_bin_type(Polygon(hex_pts))

# Irregular offcut
offcut = Polygon([(0,0),(800,0),(800,300),(500,600),(0,600)])
b.add_bin_type(offcut)

Solver

from pyckingsolver import Solver, LeftoverMode

# Auto-discover bundled binary
solver = Solver()

# Explicit binary path
solver = Solver(binary="path/to/packingsolver_irregular")

# Different problem type (rectangle-only problems)
solver = Solver(problem_type="rectangle")

solution = solver.solve(
    instance,
    time_limit=60,              # seconds
    verbosity_level=1,          # 0=quiet, 1=summary, 2=verbose
    json_output="sol.json",     # optional: save the solver certificate as-is
)

SolverParams Dataclass

For reusable configurations and IDE autocomplete, build a SolverParams dataclass once and pass it to solver.solve(...):

from pyckingsolver import Solver, SolverParams

params = SolverParams(
    time_limit=120,
    verbosity_level=1,
    optimization_mode="Anytime",
    use_tree_search=True,
    item_item_minimum_spacing=2.0,
    anchor=True,
    anchor_x_weight=1.0,
)

for instance in batch:
    sol = Solver().solve(instance, params=params)

Keyword arguments to solve() always override fields of params.

Streaming Improvements

Pass on_improvement to see provisional layouts while the solver is still searching:

solution = solver.solve(instance, time_limit=120, on_improvement=show_layout)

The Anytime solver rewrites its certificate on every improvement, so a callback forces only_write_at_the_end=False and the same 0.25 s poll that drives the adaptive stop parses each new certificate. A file caught mid-rewrite is retried on the next poll, so improvements closer together than the poll are coalesced: there is no callback per solver write.

The callback runs on the calling thread, so keep it quick and hand real work to a queue. Provisional solutions carry no metrics and the layout can still change. solve() calls it once more with exactly the Solution it returns; raising from it kills the solve, and no certificate means no callback and a None return.

Algorithm Control

Fine-tune the solver's strategy:

solution = solver.solve(
    instance,
    time_limit=120,
    # Choose optimization mode
    optimization_mode="Anytime",           # "Anytime" | "NotAnytime" | "NotAnytimeDeterministic"
    # Enable/disable algorithm components
    use_tree_search=True,
    use_sequential_single_knapsack=True,
    use_sequential_value_correction=True,
    use_column_generation=False,
    use_dichotomic_search=False,
)

Instance-Level Overrides

Override instance parameters from the solver call — useful for batch experiments:

solution = solver.solve(
    instance,
    time_limit=60,
    item_item_minimum_spacing=3.0,          # override kerf gap
    item_bin_minimum_spacing=5.0,           # override edge clearance
    leftover_mode=LeftoverMode.TOP_RIGHT,   # override scrap corner/edge
    bin_unweighted=True,                    # set bin costs to areas
    unweighted=True,                        # set item profits to areas
)

Post-Processing

Anchor items towards a corner by sliding them as close as possible without overlapping:

solution = solver.solve(
    instance,
    time_limit=60,
    anchor=True,
    anchor_x_weight=1.0,   # positive=left, negative=right, 0=off
    anchor_y_weight=1.0,   # positive=bottom, negative=top, 0=off
)

Algorithm Tuning

Advanced parameters for algorithm performance tuning:

solution = solver.solve(
    instance,
    time_limit=120,
    initial_maximum_approximation_ratio=0.20,
    maximum_approximation_ratio_factor=0.75,
    sequential_value_correction_subproblem_tree_search_queue_size=128,
    column_generation_subproblem_tree_search_queue_size=128,
    not_anytime_tree_search_queue_size=512,
)

Forward-Compatible Extra Args

Unknown CLI flags can still be passed via extra_args=["--my-flag", "value"] (field of SolverParams).

Quick Nest

For the common "pack this list of Shapely polygons" use case, nest() wraps the builder + solver into one call and adds two quality-of-life features:

1. Identical-shape grouping — duplicate Shapely polygons are collapsed into one ItemType with a copies count (compared via WKB).
2. Origin anchoring — every input is translated to its bottom-left corner before being added to the instance.

spacing is forwarded to the solver's native --item-item-minimum-spacing.

from shapely.geometry import box, Polygon
from pyckingsolver import nest, Objective

shapes = [box(0, 0, 80, 60) for _ in range(20)]
shapes += [Polygon([(0,0), (50,0), (25,40)]) for _ in range(8)]

sol = nest(
    shapes,
    bins=(1200, 600),                 # or a Polygon, or a list of either
    objective=Objective.BIN_PACKING,
    spacing=2.0,                      # 2mm kerf, enforced natively by the solver
    allowed_rotations=[(0, 0), (90, 90)],
    bin_copies=10,
    time_limit=30,
)

for it in sol.all_items():
    poly = sol.placed_shapes(it)[0]   # already mirrored/rotated/translated
    print(it.item_type_id, poly.bounds)

nest() accepts the same keyword arguments as Solver.solve() (e.g. time_limit, params=SolverParams(...), json_output, on_improvement).

Pass any CLI flag directly for new solver features:

solution = solver.solve(instance, extra_args=["--some-new-flag", "value"])

Solution

solution.total_item_count()     # int: total items placed
solution.total_bins_used()      # int: total bins used
solution.all_items()            # list[SolutionItem]: flat, across all bins

for sbin in solution.bins:
    sbin.bin_type_id            # which bin type
    sbin.copies                 # copies of this bin used
    sbin.items                  # list[SolutionItem]

for item in solution.all_items():
    item.item_type_id           # which item type
    item.x, item.y              # placement position
    item.angle                  # rotation in degrees
    item.mirror                 # bool: mirrored?
    item.shapes                 # list[Polygon] — absolute coordinates, ready to use

Solver Metrics

After solving, solution.metrics contains statistics from the C++ solver:

solution = solver.solve(instance, time_limit=30)

print(solution.metrics)
# {
#     "NumberOfItems": 16,
#     "ItemArea": 48000.0,
#     "ItemProfit": 48000.0,
#     "NumberOfBins": 1,
#     "BinArea": 720000.0,
#     "BinCost": 720000.0,
#     "FullWaste": 672000.0,
#     "FullWastePercentage": 93.33,
#     "XMax": 1200.0,
#     "YMax": 600.0,
#     "DensityX": 0.067,
#     "DensityY": 0.133,
#     "LeftoverValue": 0.0,
#     ...
# }

# Access individual metrics
waste_pct = solution.metrics.get("FullWastePercentage", 0)
density_x = solution.metrics.get("DensityX", 0)

Export to DXF / SVG / other formats

import ezdxf  # pip install ezdxf

doc = ezdxf.new()
msp = doc.modelspace()
for item in solution.all_items():
    for poly in item.shapes:
        pts = list(poly.exterior.coords)
        msp.add_lwpolyline(pts, close=True)
doc.saveas("output.dxf")

JSON I/O

Compatible with the C++ solver's JSON format:

# Save/load instance
instance.to_json("problem.json")
instance = Instance.from_json("problem.json")

# Dict round-trip (for custom serialization)
d = instance.to_dict()
instance = Instance.from_dict(d)

# Load / save solution
solution = Solution.from_json("solution.json")

Geometry Helpers

from pyckingsolver import (
    shape_to_json,          # Shapely Polygon → solver JSON dict
    shape_from_json,        # solver JSON dict → Shapely Polygon
    elements_to_polygon,    # line-segment + arc elements → Shapely Polygon
    circle_polygon,         # circle → Shapely polygon
    rectangle_polygon,      # rectangle → Shapely polygon
)
from shapely.geometry import Polygon

# Export any Shapely polygon to solver JSON (CCW winding enforced automatically)
data = shape_to_json(Polygon([(0, 0), (50, 0), (25, 40)]))   # {"type": "polygon", ...}

# Parse a solver shape dict back to Shapely
poly = shape_from_json({"type": "rectangle", "width": 80, "height": 40})

# Convert arc-based C++ solution geometry to Shapely
poly = elements_to_polygon(elements, arc_resolution=64)

# Circle / rectangle → Shapely polygon (the form the solver accepts)
circle = circle_polygon(radius=50, center=(100, 100), resolution=64)
rect = rectangle_polygon(80, 40)

Building the Solver

Pre-built binaries are bundled in the pip wheel for Windows x64 and Linux x64.

For other platforms, build from the included submodule:

git clone --recurse-submodules https://github.com/HamzaYslmn/pyckingsolver.git
cd pyckingsolver/extern/packingsolver

# Ubuntu: sudo apt-get install liblapack-dev libbz2-dev
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --config Release --parallel

# Binary location:
# Linux:   extern/packingsolver/build/src/irregular/packingsolver_irregular
# Windows: extern/packingsolver/build/src/irregular/Release/packingsolver_irregular.exe

Then point the solver at it:

solver = Solver(binary="extern/packingsolver/build/src/irregular/packingsolver_irregular")

Updating the C++ Solver

git -C extern/packingsolver pull origin master
git add extern/packingsolver
git commit -m "Update solver submodule"

How It Works

Python (Shapely)  →  JSON  →  C++ Solver  →  JSON  →  Python (Shapely)
  InstanceBuilder   instance   optimize     solution    Solution

1. Build — define bins and items as Shapely Polygons via InstanceBuilder
2. Serialize — convert to PackingSolver JSON (CCW winding enforced, holes as interior rings)
3. Solve — C++ solver runs branch-and-bound / heuristics
4. Parse — placed items returned as Shapely geometries in absolute coordinates

The C++ solver (fontanf/packingsolver) also supports rectangle, box (3D), guillotine cut, and 1D packing — accessible by passing problem_type to Solver().

License

AGPL-3.0-or-later, see LICENSE.

Based on PackingSolver by Florian Fontan, which is MIT licensed. The wheels bundle a compiled packingsolver_irregular, so upstream's notice ships with them as LICENSE.packingsolver.

The binary is built with -DPACKINGSOLVER_USE_CLP=OFF. That flag is load bearing: Clp, CoinUtils and Osi are EPL-2.0, which does not combine with the AGPL. HiGHS (the solver actually used), Boost, nlohmann/json and every fontanf dependency are MIT or BSL-1.0 and combine fine.