secnot / rectpack

Python 2D rectangle packing library
Apache License 2.0
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rectpack Build Status

Rectpack is a collection of heuristic algorithms for solving the 2D knapsack problem, also known as the bin packing problem. In essence packing a set of rectangles into the smallest number of bins.

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Installation

Download the package or clone the repository, and then install with:

python setup.py install

or use pypi:

pip install rectpack

Basic Usage

Packing rectangles into a number of bins is very simple:

from rectpack import newPacker

rectangles = [(100, 30), (40, 60), (30, 30),(70, 70), (100, 50), (30, 30)]
bins = [(300, 450), (80, 40), (200, 150)]

packer = newPacker()

# Add the rectangles to packing queue
for r in rectangles:
    packer.add_rect(*r)

# Add the bins where the rectangles will be placed
for b in bins:
    packer.add_bin(*b)

# Start packing
packer.pack()

Once the rectangles have been packed the results can be accessed individually

# Obtain number of bins used for packing
nbins = len(packer)

# Index first bin
abin = packer[0]

# Bin dimmensions (bins can be reordered during packing)
width, height = abin.width, abin.height

# Number of rectangles packed into first bin
nrect = len(packer[0])

# Second bin first rectangle
rect = packer[1][0]

# rect is a Rectangle object
x = rect.x # rectangle bottom-left x coordinate
y = rect.y # rectangle bottom-left y coordinate
w = rect.width
h = rect.height

looping over all of them

for abin in packer:
  print(abin.bid) # Bin id if it has one
  for rect in abin:
    print(rect)

or using rect_list()

# Full rectangle list
all_rects = packer.rect_list()
for rect in all_rects:
    b, x, y, w, h, rid = rect

# b - Bin index
# x - Rectangle bottom-left corner x coordinate
# y - Rectangle bottom-left corner y coordinate
# w - Rectangle width
# h - Rectangle height
# rid - User asigned rectangle id or None

Lastly all the dimmension (bins and rectangles) must be integers or decimals to avoid collisions caused by floating point rounding. If your data is floating point use float2dec to convert float values to decimals (see float below)

API

A more detailed description of API calls:

Supported Algorithms

This library implements three of the algorithms described in [1] Skyline, Maxrects, and Guillotine, with the following variants:

I recommend to use the default algorithm unless the packing is too slow, in that case switch to one of the Guillotine variants for example GuillotineBssfSas. You can learn more about the algorithms in [1].

Testing

Rectpack is thoroughly tested, run the tests with:

python setup.py test

or

python -m unittest discover

Float

If you need to use floats just convert them to fixed-point using a Decimal type, be carefull rounding up so the actual rectangle size is always smaller than the conversion. Rectpack provides helper funcion float2dec for this task, it accepts a number and the number of decimals to round to, and returns the rounded Decimal.

    from rectpack import float2dec, newPacker

    float_rects = [...]
    dec_rects = [(float2dec(r[0], 3), float2dec(r[1], 3)) for r in float_rects]

    p = newPacker()
    ...

References

[1] Jukka Jylang - A Thousand Ways to Pack the Bin - A Practical Approach to Two-Dimensional Rectangle Bin Packing (2010)

[2] Huang, E. Korf - Optimal Rectangle Packing: An Absolute Placement Approach (2013)