diff --git a/examples/pcgen.py b/examples/pcgen.py
new file mode 100644
index 0000000..3c25ed6
--- /dev/null
+++ b/examples/pcgen.py
@@ -0,0 +1,298 @@
+"""
+Routines for creating normalized 2D lattices and common photonic crystal
+ cavity designs.
+"""
+
+from typing import Sequence, Tuple
+
+import numpy        # type: ignore
+
+
+def triangular_lattice(dims: Tuple[int, int],
+                       asymmetric: bool = False,
+                       origin: str = 'center',
+                       ) -> numpy.ndarray:
+    """
+    Return an ndarray of `[[x0, y0], [x1, y1], ...]` denoting lattice sites for
+     a triangular lattice in 2D.
+
+    Args:
+        dims: Number of lattice sites in the [x, y] directions.
+        asymmetric: If true, each row will contain the same number of
+            x-coord lattice sites. If false, every other row will be
+            one site shorter (to make the structure symmetric).
+        origin: If 'corner', the least-(x,y) lattice site is placed at (0, 0)
+            If 'center', the center of the lattice (not necessarily a
+            lattice site) is placed at (0, 0).
+
+    Returns:
+        `[[x0, y0], [x1, 1], ...]` denoting lattice sites.
+    """
+    sx, sy = numpy.meshgrid(numpy.arange(dims[0], dtype=float),
+                            numpy.arange(dims[1], dtype=float), indexing='ij')
+
+    sx[sy % 2 == 1] += 0.5
+    sy *= numpy.sqrt(3) / 2
+
+    if not asymmetric:
+        which = sx != sx.max()
+        sx = sx[which]
+        sy = sy[which]
+
+    xy = numpy.column_stack((sx.flat, sy.flat))
+
+    if origin == 'center':
+        xy -= (xy.max(axis=0) - xy.min(axis=0)) / 2
+    elif origin == 'corner':
+        pass
+    else:
+        raise Exception(f'Invalid value for `origin`: {origin}')
+
+    return xy[xy[:, 0].argsort(), :]
+
+
+def square_lattice(dims: Tuple[int, int]) -> numpy.ndarray:
+    """
+    Return an ndarray of `[[x0, y0], [x1, y1], ...]` denoting lattice sites for
+     a square lattice in 2D. The lattice will be centered around (0, 0).
+
+    Args:
+        dims: Number of lattice sites in the [x, y] directions.
+
+    Returns:
+        `[[x0, y0], [x1, 1], ...]` denoting lattice sites.
+    """
+    xs, ys = numpy.meshgrid(range(dims[0]), range(dims[1]), 'xy')
+    xs -= dims[0]/2
+    ys -= dims[1]/2
+    xy = numpy.vstack((xs.flatten(), ys.flatten())).T
+    return xy[xy[:, 0].argsort(), ]
+
+
+# ### Photonic crystal functions ###
+
+
+def nanobeam_holes(a_defect: float,
+                   num_defect_holes: int,
+                   num_mirror_holes: int
+                   ) -> numpy.ndarray:
+    """
+    Returns a list of `[[x0, r0], [x1, r1], ...]` of nanobeam hole positions and radii.
+     Creates a region in which the lattice constant and radius are progressively
+     (linearly) altered over num_defect_holes holes until they reach the value
+     specified by a_defect, then symmetrically returned to a lattice constant and
+     radius of 1, which is repeated num_mirror_holes times on each side.
+
+    Args:
+        a_defect: Minimum lattice constant for the defect, as a fraction of the
+            mirror lattice constant (ie., for no defect, a_defect = 1).
+        num_defect_holes: How many holes form the defect (per-side)
+        num_mirror_holes: How many holes form the mirror (per-side)
+
+    Returns:
+        Ndarray `[[x0, r0], [x1, r1], ...]` of nanobeam hole positions and radii.
+    """
+    a_values = numpy.linspace(a_defect, 1, num_defect_holes, endpoint=False)
+    xs = a_values.cumsum() - (a_values[0] / 2)  # Later mirroring makes center distance 2x as long
+    mirror_xs = numpy.arange(1, num_mirror_holes + 1, dtype=float) + xs[-1]
+    mirror_rs = numpy.ones_like(mirror_xs)
+    return numpy.vstack((numpy.hstack((-mirror_xs[::-1], -xs[::-1], xs, mirror_xs)),
+                         numpy.hstack((mirror_rs[::-1], a_values[::-1], a_values, mirror_rs)))).T
+
+
+def waveguide(length: int, num_mirror: int) -> numpy.ndarray:
+    """
+    Line defect waveguide in a triangular lattice.
+
+    Args:
+        length: waveguide length (number of holes in x direction)
+        num_mirror: Mirror length (number of holes per side; total size is
+            `2 * n + 1` holes.
+
+    Returns:
+        `[[x0, y0], [x1, y1], ...]` for all the holes
+    """
+    p = triangular_lattice([length, 2 * num_mirror + 1])
+    p_wg = p[p[:, 1] != 0, :]
+    return p_wg
+
+
+def wgbend(num_mirror: int) -> numpy.ndarray:
+    """
+    Line defect waveguide bend in a triangular lattice.
+
+    Args:
+        num_mirror: Mirror length (number of holes per side; total size is
+            approximately `2 * n + 1`
+
+    Returns:
+        `[[x0, y0], [x1, y1], ...]` for all the holes
+    """
+    p = triangular_lattice([2 * num_mirror, 2 * num_mirror + 1])
+    left_horiz = (p[:, 1] == 0) & (p[:, 0] <= 0)
+    p = p[~left_horiz, :]
+
+    right_diag = numpy.isclose(p[:, 1], p[:, 0] * numpy.sqrt(3)) & (p[:, 0] >= 0)
+    p = p[~right_diag, :]
+    return p
+
+
+def y_splitter(num_mirror: int) -> numpy.ndarray:
+    """
+    Line defect waveguide y-splitter in a triangular lattice.
+
+    Args:
+        num_mirror: Mirror length (number of holes per side; total size is
+            approximately `2 * n + 1` holes.
+
+    Returns:
+        `[[x0, y0], [x1, y1], ...]` for all the holes
+    """
+    p = triangular_lattice([2 * num_mirror, 2 * num_mirror + 1])
+    left_horiz = (p[:, 1] == 0) & (p[:, 0] <= 0)
+    p = p[~left_horiz, :]
+
+    right_diag_up = numpy.isclose(p[:, 1], p[:, 0] * numpy.sqrt(3)) & (p[:, 0] >= 0)
+    p = p[~right_diag_up, :]
+
+    right_diag_dn = numpy.isclose(p[:, 1], -p[:, 0] * numpy.sqrt(3)) & (p[:, 0] >= 0)
+    p = p[~right_diag_dn, :]
+    return p
+
+
+def ln_defect(mirror_dims: Tuple[int, int],
+              defect_length: int,
+              ) -> numpy.ndarray:
+    """
+    N-hole defect in a triangular lattice.
+
+    Args:
+        mirror_dims: [x, y] mirror lengths (number of holes). Total number of holes
+            is 2 * n + 1 in each direction.
+        defect_length: Length of defect. Should be an odd number.
+
+    Returns:
+        `[[x0, y0], [x1, y1], ...]` for all the holes
+    """
+    if defect_length % 2 != 1:
+        raise Exception('defect_length must be odd!')
+    p = triangular_lattice([2 * d + 1 for d in mirror_dims])
+    half_length = numpy.floor(defect_length / 2)
+    hole_nums = numpy.arange(-half_length, half_length + 1)
+    holes_to_keep = numpy.in1d(p[:, 0], hole_nums, invert=True)
+    return p[numpy.logical_or(holes_to_keep, p[:, 1] != 0), ]
+
+
+def ln_shift_defect(mirror_dims: Tuple[int, int],
+                    defect_length: int,
+                    shifts_a: Sequence[float] = (0.15, 0, 0.075),
+                    shifts_r: Sequence[float] = (1, 1, 1)
+                    ) -> numpy.ndarray:
+    """
+    N-hole defect with shifted holes (intended to give the mode a gaussian profile
+     in real- and k-space so as to improve both Q and confinement). Holes along the
+     defect line are shifted and altered according to the shifts_* parameters.
+
+    Args:
+        mirror_dims: [x, y] mirror lengths (number of holes). Total number of holes
+            is `2 * n + 1` in each direction.
+        defect_length: Length of defect. Should be an odd number.
+        shifts_a: Percentage of a to shift (1st, 2nd, 3rd,...) holes along the defect line
+        shifts_r: Factor to multiply the radius by. Should match length of shifts_a
+
+    Returns:
+        `[[x0, y0, r0], [x1, y1, r1], ...]` for all the holes
+    """
+    if not hasattr(shifts_a, "__len__") and shifts_a is not None:
+        shifts_a = [shifts_a]
+    if not hasattr(shifts_r, "__len__") and shifts_r is not None:
+        shifts_r = [shifts_r]
+
+    xy = ln_defect(mirror_dims, defect_length)
+
+    # Add column for radius
+    xyr = numpy.hstack((xy, numpy.ones((xy.shape[0], 1))))
+
+    # Shift holes
+    # Expand shifts as necessary
+    n_shifted = max(len(shifts_a), len(shifts_r))
+
+    tmp_a = numpy.array(shifts_a)
+    shifts_a = numpy.ones((n_shifted, ))
+    shifts_a[:len(tmp_a)] = tmp_a
+
+    tmp_r = numpy.array(shifts_r)
+    shifts_r = numpy.ones((n_shifted, ))
+    shifts_r[:len(tmp_r)] = tmp_r
+
+    x_removed = numpy.floor(defect_length / 2)
+
+    for ind in range(n_shifted):
+        for sign in (-1, 1):
+            x_val = sign * (x_removed + ind + 1)
+            which = numpy.logical_and(xyr[:, 0] == x_val, xyr[:, 1] == 0)
+            xyr[which, ] = (x_val + numpy.sign(x_val) * shifts_a[ind], 0, shifts_r[ind])
+
+    return xyr
+
+
+def r6_defect(mirror_dims: Tuple[int, int]) -> numpy.ndarray:
+    """
+    R6 defect in a triangular lattice.
+
+    Args:
+        mirror_dims: [x, y] mirror lengths (number of holes). Total number of holes
+            is 2 * n + 1 in each direction.
+
+    Returns:
+        `[[x0, y0], [x1, y1], ...]` specifying hole centers.
+    """
+    xy = triangular_lattice([2 * d + 1 for d in mirror_dims])
+
+    rem_holes_plus = numpy.array([[1, 0],
+                                  [0.5, +numpy.sqrt(3)/2],
+                                  [0.5, -numpy.sqrt(3)/2]])
+    rem_holes = numpy.vstack((rem_holes_plus, -rem_holes_plus))
+
+    for rem_xy in rem_holes:
+        xy = xy[(xy != rem_xy).any(axis=1), ]
+
+    return xy
+
+
+def l3_shift_perturbed_defect(
+    mirror_dims: Tuple[int, int],
+    perturbed_radius: float = 1.1,
+    shifts_a: Sequence[float] = (),
+    shifts_r: Sequence[float] = ()
+    ) -> numpy.ndarray:
+    """
+    3-hole defect with perturbed hole sizes intended to form an upwards-directed
+     beam. Can also include shifted holes along the defect line, intended
+     to give the mode a more gaussian profile to improve Q.
+
+    Args:
+        mirror_dims: [x, y] mirror lengths (number of holes). Total number of holes
+            is 2 * n + 1 in each direction.
+        perturbed_radius: Amount to perturb the radius of the holes used for beam-forming
+        shifts_a: Percentage of a to shift (1st, 2nd, 3rd,...) holes along the defect line
+        shifts_r: Factor to multiply the radius by. Should match length of shifts_a
+
+    Returns:
+        `[[x0, y0, r0], [x1, y1, r1], ...]` for all the holes
+    """
+    xyr = ln_shift_defect(mirror_dims, 3, shifts_a, shifts_r)
+
+    abs_x, abs_y = (numpy.fabs(xyr[:, i]) for i in (0, 1))
+
+    # Sorted unique xs and ys
+    # Ignore row y=0 because it might have shifted holes
+    xs = numpy.unique(abs_x[abs_x != 0])
+    ys = numpy.unique(abs_y)
+
+    # which holes should be perturbed? (xs[[3, 7]], ys[1]) and (xs[[2, 6]], ys[2])
+    perturbed_holes = ((xs[a], ys[b]) for a, b in ((3, 1), (7, 1), (2, 2), (6, 2)))
+    for row in xyr:
+        if numpy.fabs(row) in perturbed_holes:
+            row[2] = perturbed_radius
+    return xyr
diff --git a/examples/phc.py b/examples/phc.py
new file mode 100644
index 0000000..f214a5a
--- /dev/null
+++ b/examples/phc.py
@@ -0,0 +1,178 @@
+from typing import Tuple, Sequence
+
+import numpy        # type: ignore
+from numpy import pi
+
+from masque import layer_t, Pattern, SubPattern, Label
+from masque.shapes import Polygon, Circle
+from masque.builder import Device, Port
+from masque.library import Library, DeviceLibrary
+from masque.file.klamath import writefile
+
+import pcgen
+
+
+HOLE_SCALE: float = 1000
+''' Radius for the 'hole' cell. Should be significantly bigger than
+    1 (minimum database unit) in order to have enough precision to
+    reasonably represent a polygonized circle (for GDS)
+'''
+
+def hole(layer: layer_t,
+         radius: float = HOLE_SCALE * 0.35,
+         ) -> Pattern:
+    """
+    Generate a pattern containing a single circular hole.
+
+    Args:
+        layer: Layer to draw the circle on.
+        radius: Circle radius.
+
+    Returns:
+        Pattern, named `'hole'`
+    """
+    pat = Pattern('hole', shapes=[
+        Circle(radius=radius, offset=(0, 0), layer=layer, dose=1.0)
+        ])
+    return pat
+
+
+def perturbed_l3(lattice_constant: float,
+                 hole: Pattern,
+                 trench_dose: float = 1.0,
+                 trench_layer: layer_t = (1, 0),
+                 shifts_a: Sequence[float] = (0.15, 0, 0.075),
+                 shifts_r: Sequence[float] = (1.0, 1.0, 1.0),
+                 xy_size: Tuple[int, int] = (10, 10),
+                 perturbed_radius: float = 1.1,
+                 trench_width: float = 1200,
+                 ) -> Device:
+    """
+    Generate a `Device` representing a perturbed L3 cavity.
+
+    Args:
+        lattice_constant: Distance between nearest neighbor holes
+        hole: `Pattern` object containing a single hole
+        trench_dose: Dose for the trenches. Default 1.0. (Hole dose is 1.0.)
+        trench_layer: Layer for the trenches, default `(1, 0)`.
+        shifts_a: passed to `pcgen.l3_shift`; specifies lattice constant
+            (1 - multiplicative factor) for shifting holes adjacent to
+            the defect (same row). Default `(0.15, 0, 0.075)` for first,
+            second, third holes.
+        shifts_r: passed to `pcgen.l3_shift`; specifies radius for perturbing
+            holes adjacent to the defect (same row). Default 1.0 for all holes.
+            Provided sequence should have same length as `shifts_a`.
+        xy_size: `(x, y)` number of mirror periods in each direction; total size is
+                `2 * n + 1` holes in each direction. Default (10, 10).
+        perturbed_radius: radius of holes perturbed to form an upwards-driected beam
+                (multiplicative factor). Default 1.1.
+        trench width: Width of the undercut trenches. Default 1200.
+
+    Returns:
+        `Device` object representing the L3 design.
+    """
+    xyr = pcgen.l3_shift_perturbed_defect(mirror_dims=xy_size,
+                                          perturbed_radius=perturbed_radius,
+                                          shifts_a=shifts_a,
+                                          shifts_r=shifts_r)
+
+    pat = Pattern(f'L3p-a{lattice_constant:g}rp{perturbed_radius:g}')
+    pat.subpatterns += [SubPattern(hole, offset=(lattice_constant * x,
+                                                 lattice_constant * y), scale=r * lattice_constant / HOLE_SCALE)
+                        for x, y, r in xyr]
+
+    min_xy, max_xy = pat.get_bounds()
+    trench_dx = max_xy[0] - min_xy[0]
+
+    pat.shapes += [
+        Polygon.rect(ymin=max_xy[1], xmin=min_xy[0], lx=trench_dx, ly=trench_width,
+                     layer=trench_layer, dose=trench_dose),
+        Polygon.rect(ymax=min_xy[1], xmin=min_xy[0], lx=trench_dx, ly=trench_width,
+                     layer=trench_layer, dose=trench_dose),
+        ]
+
+    ports = {
+        'input': Port((-lattice_constant * xy_size[0], 0), rotation=0, ptype=1),
+        'output': Port((lattice_constant * xy_size[0], 0), rotation=pi, ptype=1),
+        }
+
+    return Device(pat, ports)
+
+
+def waveguide(lattice_constant: float,
+              hole: Pattern,
+              length: int,
+              mirror_periods: int,
+              ) -> Device:
+    xy = pcgen.waveguide(length=length + 2, num_mirror=mirror_periods)
+
+    pat = Pattern(f'_wg-a{lattice_constant:g}l{length}')
+    pat.subpatterns += [SubPattern(hole, offset=(lattice_constant * x,
+                                                 lattice_constant * y), scale=lattice_constant / HOLE_SCALE)
+                        for x, y in xy]
+
+    ports = {
+        'left': Port((-lattice_constant * length / 2, 0), rotation=0, ptype=1),
+        'right': Port((lattice_constant * length / 2, 0), rotation=pi, ptype=1),
+        }
+    return Device(pat, ports)
+
+
+def bend(lattice_constant: float,
+         hole: Pattern,
+         mirror_periods: int,
+         ) -> Device:
+    xy = pcgen.wgbend(num_mirror=mirror_periods)
+
+    pat_half = Pattern(f'_wgbend_half-a{lattice_constant:g}l{mirror_periods}')
+    pat_half.subpatterns += [SubPattern(hole, offset=(lattice_constant * x,
+                                                      lattice_constant * y), scale=lattice_constant / HOLE_SCALE)
+                             for x, y in xy]
+
+    pat = Pattern(f'_wgbend-a{lattice_constant:g}l{mirror_periods}')
+    pat.addsp(pat_half, offset=(0, 0), rotation=0, mirrored=(False, False))
+    pat.addsp(pat_half, offset=(0, 0), rotation=-2 * pi / 3, mirrored=(True, False))
+
+
+    ports = {
+        'left': Port((-lattice_constant * mirror_periods, 0), rotation=0, ptype=1),
+        'right': Port((lattice_constant * mirror_periods / 2,
+                       lattice_constant * mirror_periods * numpy.sqrt(3) / 2), rotation=pi * 4 / 3, ptype=1),
+        }
+    return Device(pat, ports)
+
+
+def label_ports(device: Device, layer: layer_t = (3, 0)) -> Device:
+    for name, port in device.ports.items():
+        angle_deg = numpy.rad2deg(port.rotation)
+        device.pattern.labels += [
+            Label(string=f'{name} (angle {angle_deg:g})', layer=layer, offset=port.offset)
+            ]
+    return device
+
+
+def main():
+    hole_layer = (1, 2)
+    a = 512
+    hole_pat = hole(layer=hole_layer)
+    wg0 = label_ports(waveguide(lattice_constant=a, hole=hole_pat, length=10, mirror_periods=5))
+    wg1 = label_ports(waveguide(lattice_constant=a, hole=hole_pat, length=5, mirror_periods=5))
+    bend0 = label_ports(bend(lattice_constant=a, hole=hole_pat, mirror_periods=5))
+    l3cav = label_ports(perturbed_l3(lattice_constant=a, hole=hole_pat, xy_size=(4, 10)))
+
+    dev = Device(name='my_bend', ports={})
+    dev.place(wg0, offset=(0, 0), port_map={'left': 'in', 'right': 'signal'})
+    dev.plug(wg0, {'signal': 'left'})
+    dev.plug(bend0, {'signal': 'left'})
+    dev.plug(wg1, {'signal': 'left'})
+    dev.plug(bend0, {'signal': 'right'})
+    dev.plug(wg0, {'signal': 'left'})
+    dev.plug(l3cav, {'signal': 'input'})
+    dev.plug(wg0, {'signal': 'left'})
+
+    writefile(dev.pattern, 'phc.gds', 1e-9, 1e-3)
+    dev.pattern.visualize()
+
+
+if __name__ == '__main__':
+    main()
diff --git a/masque/VERSION b/masque/VERSION
deleted file mode 100644
index 8bbe6cf..0000000
--- a/masque/VERSION
+++ /dev/null
@@ -1 +0,0 @@
-2.2
diff --git a/masque/VERSION.py b/masque/VERSION.py
new file mode 100644
index 0000000..12d4cbb
--- /dev/null
+++ b/masque/VERSION.py
@@ -0,0 +1,4 @@
+""" VERSION defintion. THIS FILE IS MANUALLY PARSED BY setup.py and REQUIRES A SPECIFIC FORMAT """
+__version__ = '''
+2.4
+'''
diff --git a/masque/__init__.py b/masque/__init__.py
index 87ceb5d..611d4d4 100644
--- a/masque/__init__.py
+++ b/masque/__init__.py
@@ -2,9 +2,9 @@
  masque 2D CAD library
 
  masque is an attempt to make a relatively small library for designing lithography
-  masks. The general idea is to implement something resembling the GDSII file-format, but
-  with some vectorized element types (eg. circles, not just polygons), better support for
-  E-beam doses, and the ability to output to multiple formats.
+  masks. The general idea is to implement something resembling the GDSII and OASIS file-formats,
+  but with some additional vectorized element types (eg. ellipses, not just polygons), better
+  support for E-beam doses, and the ability to interface with multiple file formats.
 
  `Pattern` is a basic object containing a 2D lithography mask, composed of a list of `Shape`
   objects, a list of `Label` objects, and a list of references to other `Patterns` (using
@@ -15,9 +15,18 @@
 
  Note that the methods for these classes try to avoid copying wherever possible, so unless
   otherwise noted, assume that arguments are stored by-reference.
-"""
 
-import pathlib
+
+ NOTES ON INTERNALS
+ ==========================
+ - Many of `masque`'s classes make use of `__slots__` to make them faster / smaller.
+    Since `__slots__` doesn't play well with multiple inheritance, the `masque.utils.AutoSlots`
+    metaclass is used to auto-generate slots based on superclass type annotations.
+ - File I/O submodules are imported by `masque.file` to avoid creating hard dependencies on
+    external file-format reader/writers
+ - Pattern locking/unlocking is quite slow for large hierarchies.
+
+"""
 
 from .error import PatternError, PatternLockedError
 from .shapes import Shape
@@ -25,11 +34,10 @@ from .label import Label
 from .subpattern import SubPattern
 from .pattern import Pattern
 from .utils import layer_t, annotations_t
-from .library import Library
+from .library import Library, DeviceLibrary
 
 
 __author__ = 'Jan Petykiewicz'
 
-with open(pathlib.Path(__file__).parent / 'VERSION', 'r') as f:
-    __version__ = f.read().strip()
-version = __version__
+from .VERSION import __version__
+version = __version__       # legacy
diff --git a/masque/builder/__init__.py b/masque/builder/__init__.py
new file mode 100644
index 0000000..50ddcee
--- /dev/null
+++ b/masque/builder/__init__.py
@@ -0,0 +1,2 @@
+from .devices import Port, Device
+from .utils import ell
diff --git a/masque/builder/devices.py b/masque/builder/devices.py
new file mode 100644
index 0000000..519462f
--- /dev/null
+++ b/masque/builder/devices.py
@@ -0,0 +1,726 @@
+from typing import Dict, Iterable, List, Tuple, Union, TypeVar, Any, Iterator, Optional, Sequence
+import copy
+import warnings
+import logging
+from collections import Counter
+
+import numpy        # type: ignore
+from numpy import pi
+
+from ..pattern import Pattern
+from ..subpattern import SubPattern
+from ..traits import PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable
+from ..utils import AutoSlots, rotation_matrix_2d, vector2
+from ..error import DeviceError
+
+
+logger = logging.getLogger(__name__)
+
+
+P = TypeVar('P', bound='Port')
+D = TypeVar('D', bound='Device')
+O = TypeVar('O', bound='Device')
+
+
+class Port(PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable, metaclass=AutoSlots):
+    """
+    A point at which a `Device` can be snapped to another `Device`.
+
+    Each port has an `offset` ((x, y) position) and may also have a
+      `rotation` (orientation) and a `ptype` (port type).
+
+    The `rotation` is an angle, in radians, measured counterclockwise
+      from the +x axis, pointing inwards into the device which owns the port.
+      The rotation may be set to `None`, indicating that any orientation is
+      allowed (e.g. for a DC electrical port). It is stored modulo 2pi.
+
+    The `ptype` is an arbitrary integer, default of `0`.
+    """
+    __slots__ = ('ptype', '_rotation')
+
+    _rotation: Optional[float]
+    """ radians counterclockwise from +x, pointing into device body.
+        Can be `None` to signify undirected port """
+
+    ptype: int
+    """ Port types must match to be plugged together if both are non-zero """
+
+    def __init__(self,
+                 offset: numpy.ndarray,
+                 rotation: Optional[float],
+                 ptype: int = 0,
+                 ) -> None:
+        self.offset = offset
+        self.rotation = rotation
+        self.ptype = ptype
+
+    @property
+    def rotation(self) -> Optional[float]:
+        """ Rotation, radians counterclockwise, pointing into device body. Can be None. """
+        return self._rotation
+
+    @rotation.setter
+    def rotation(self, val: float):
+        if val is None:
+            self._rotation = None
+        else:
+            if not numpy.size(val) == 1:
+                raise DeviceError('Rotation must be a scalar')
+            self._rotation = val % (2 * pi)
+
+    def get_bounds(self):
+        return numpy.vstack((self.offset, self.offset))
+
+    def set_ptype(self: P, ptype: int) -> P:
+        """ Chainable setter for `ptype` """
+        self.ptype = ptype
+        return self
+
+    def mirror(self: P, axis: int) -> P:
+        self.offset[1 - axis] *= -1
+        if self.rotation is not None:
+            self.rotation *= -1
+            self.rotation += axis * pi
+        return self
+
+    def rotate(self: P, rotation: float) -> P:
+        if self.rotation is not None:
+            self.rotation += rotation
+        return self
+
+    def set_rotation(self: P, rotation: Optional[float]) -> P:
+        self.rotation = rotation
+        return self
+
+    def __repr__(self) -> str:
+        if self.rotation is None:
+            rot = 'any'
+        else:
+            rot = str(numpy.rad2deg(self.rotation))
+        return f'<{self.offset}, {rot}, [{self.ptype}]>'
+
+
+class Device(Copyable, Mirrorable):
+    """
+    A `Device` is a combination of a `Pattern` with a set of named `Port`s
+      which can be used to "snap" devices together to make complex layouts.
+
+    `Device`s can be as simple as one or two ports (e.g. an electrical pad
+    or wire), but can also be used to build and represent a large routed
+    layout (e.g. a logical block with multiple I/O connections or even a
+    full chip).
+
+    For convenience, ports can be read out using square brackets:
+    - `device['A'] == Port((0, 0), 0)`
+    - `device[['A', 'B']] == {'A': Port((0, 0), 0), 'B': Port((0, 0), pi)}`
+
+    Examples: Creating a Device
+    ===========================
+    - `Device(pattern, ports={'A': port_a, 'C': port_c})` uses an existing
+        pattern and defines some ports.
+
+    - `Device(name='my_dev_name', ports=None)` makes a new empty pattern with
+        default ports ('A' and 'B', in opposite directions, at (0, 0)).
+
+    - `my_device.build('my_layout')` makes a new pattern and instantiates
+        `my_device` in it with offset (0, 0) as a base for further building.
+
+    - `my_device.as_interface('my_component', port_map=['A', 'B'])` makes a new
+        (empty) pattern, copies over ports 'A' and 'B' from `my_device`, and
+        creates additional ports 'in_A' and 'in_B' facing in the opposite
+        directions. This can be used to build a device which can plug into
+        `my_device` (using the 'in_*' ports) but which does not itself include
+        `my_device` as a subcomponent.
+
+    Examples: Adding to a Device
+    ============================
+    - `my_device.plug(subdevice, {'A': 'C', 'B': 'B'}, map_out={'D': 'myport'})`
+        instantiates `subdevice` into `my_device`, plugging ports 'A' and 'B'
+        of `my_device` into ports 'C' and 'B' of `subdevice`. The connected ports
+        are removed and any unconnected ports from `subdevice` are added to
+        `my_device`. Port 'D' of `subdevice` (unconnected) is renamed to 'myport'.
+
+    - `my_device.plug(wire, {'myport': 'A'})` places port 'A' of `wire` at 'myport'
+        of `my_device`. If `wire` has only two ports (e.g. 'A' and 'B'), no `map_out`,
+        argument is provided, and the `inherit_name` argument is not explicitly
+        set to `False`, the unconnected port of `wire` is automatically renamed to
+        'myport'. This allows easy extension of existing ports without changing
+        their names or having to provide `map_out` each time `plug` is called.
+
+    - `my_device.place(pad, offset=(10, 10), rotation=pi / 2, port_map={'A': 'gnd'})`
+        instantiates `pad` at the specified (x, y) offset and with the specified
+        rotation, adding its ports to those of `my_device`. Port 'A' of `pad` is
+        renamed to 'gnd' so that further routing can use this signal or net name
+        rather than the port name on the original `pad` device.
+    """
+    __slots__ = ('pattern', 'ports', '_dead')
+
+    pattern: Pattern
+    """ Layout of this device """
+
+    ports: Dict[str, Port]
+    """ Uniquely-named ports which can be used to snap to other Device instances"""
+
+    _dead: bool
+    """ If True, plug()/place() are skipped (for debugging)"""
+
+    def __init__(self,
+                 pattern: Optional[Pattern] = None,
+                 ports: Optional[Dict[str, Port]] = None,
+                 *,
+                 name: Optional[str] = None,
+                 ) -> None:
+        """
+        If `ports` is `None`, two default ports ('A' and 'B') are created.
+        Both are placed at (0, 0) and have `ptype=0`, but 'A' has rotation 0
+          (attached devices will be placed to the left) and 'B' has rotation
+          pi (attached devices will be placed to the right).
+        """
+        if pattern is not None:
+            if name is not None:
+                raise DeviceError('Only one of `pattern` and `name` may be specified')
+            self.pattern = pattern
+        else:
+            if name is None:
+                raise DeviceError('Must specify either `pattern` or `name`')
+            self.pattern = Pattern(name=name)
+
+        if ports is None:
+            self.ports = {
+                'A': Port([0, 0], rotation=0, ptype=0),
+                'B': Port([0, 0], rotation=pi, ptype=0),
+                }
+        else:
+            self.ports = copy.deepcopy(ports)
+
+        self._dead = False
+
+    def __getitem__(self, key: Union[str, Iterable[str]]) -> numpy.ndarray:
+        """
+        For convenience, ports can be read out using square brackets:
+        - `device['A'] == Port((0, 0), 0)`
+        - `device[['A', 'B']] == {'A': Port((0, 0), 0),
+                                  'B': Port((0, 0), pi)}`
+        """
+        if isinstance(key, str):
+            return self.ports[key]
+        else:
+            return {k: self.ports[k] for k in key}
+
+    def rename_ports(self: D,
+                     mapping: Dict[str, Optional[str]],
+                     overwrite: bool = False,
+                     ) -> D:
+        """
+        Renames ports as specified by `mapping`.
+        Ports can be explicitly deleted by mapping them to `None`.
+
+        Args:
+            mapping: Dict of `{'old_name': 'new_name'}` pairs. Names can be mapped
+                to `None` to perform an explicit deletion. `'new_name'` can also
+                overwrite an existing non-renamed port to implicitly delete it if
+                `overwrite` is set to `True`.
+            overwrite: Allows implicit deletion of ports if set to `True`; see `mapping`.
+
+        Returns:
+            self
+        """
+        if not overwrite:
+            duplicates = (set(self.ports.keys()) - set(mapping.keys())) & set(mapping.values())
+            if duplicates:
+                raise DeviceError(f'Unrenamed ports would be overwritten: {duplicates}')
+
+        renamed = {mapping[k]: self.ports.pop(k) for k in mapping.keys()}
+        if None in renamed:
+            del renamed[None]
+
+        self.ports.update(renamed)      # type: ignore
+        return self
+
+    def check_ports(self: D,
+                    other_names: Iterable[str],
+                    map_in: Optional[Dict[str, str]] = None,
+                    map_out: Optional[Dict[str, Optional[str]]] = None,
+                    ) -> D:
+        """
+        Given the provided port mappings, check that:
+            - All of the ports specified in the mappings exist
+            - There are no duplicate port names after all the mappings are performed
+
+        Args:
+            other_names: List of port names being considered for inclusion into
+                `self.ports` (before mapping)
+            map_in: Dict of `{'self_port': 'other_port'}` mappings, specifying
+                port connections between the two devices.
+            map_out: Dict of `{'old_name': 'new_name'}` mappings, specifying
+                new names for unconnected `other_names` ports.
+
+        Returns:
+            self
+
+        Raises:
+            `DeviceError` if any ports specified in `map_in` or `map_out` do not
+                exist in `self.ports` or `other_names`.
+            `DeviceError` if there are any duplicate names after `map_in` and `map_out`
+                are applied.
+        """
+        if map_in is None:
+            map_in = {}
+
+        if map_out is None:
+            map_out = {}
+
+        other = set(other_names)
+
+        missing_inkeys = set(map_in.keys()) - set(self.ports.keys())
+        if missing_inkeys:
+            raise DeviceError(f'`map_in` keys not present in device: {missing_inkeys}')
+
+        missing_invals = set(map_in.values()) - other
+        if missing_invals:
+            raise DeviceError(f'`map_in` values not present in other device: {missing_invals}')
+
+        missing_outkeys = set(map_out.keys()) - other
+        if missing_outkeys:
+            raise DeviceError(f'`map_out` keys not present in other device: {missing_outkeys}')
+
+        orig_remaining = set(self.ports.keys()) - set(map_in.keys())
+        other_remaining = other - set(map_out.keys()) - set(map_in.values())
+        mapped_vals = set(map_out.values())
+        mapped_vals.discard(None)
+
+        conflicts_final = orig_remaining & (other_remaining | mapped_vals)
+        if conflicts_final:
+            raise DeviceError(f'Device ports conflict with existing ports: {conflicts_final}')
+
+        conflicts_partial = other_remaining & mapped_vals
+        if conflicts_partial:
+            raise DeviceError(f'`map_out` targets conflict with non-mapped outputs: {conflicts_partial}')
+
+        map_out_counts = Counter(map_out.values())
+        map_out_counts[None] = 0
+        conflicts_out = {k for k, v in map_out_counts.items() if v > 1}
+        if conflicts_out:
+            raise DeviceError(f'Duplicate targets in `map_out`: {conflicts_out}')
+
+        return self
+
+    def build(self, name: str) -> 'Device':
+        """
+        Begin building a new device around an instance of the current device
+          (rather than modifying the current device).
+
+        Args:
+            name: A name for the new device
+
+        Returns:
+            The new `Device` object.
+        """
+        pat = Pattern(name)
+        pat.addsp(self.pattern)
+        new = Device(pat, ports=self.ports)
+        return new
+
+    def as_interface(self,
+                     name: str,
+                     in_prefix: str = 'in_',
+                     out_prefix: str = '',
+                     port_map: Optional[Union[Dict[str, str], Sequence[str]]] = None
+                     ) -> 'Device':
+        """
+        Begin building a new device based on all or some of the ports in the
+          current device. Do not include the current device; instead use it
+          to define ports (the "interface") for the new device.
+
+        The ports specified by `port_map` (default: all ports) are copied to
+          new device, and additional (input) ports are created facing in the
+          opposite directions. The specified `in_prefix` and `out_prefix` are
+          prepended to the port names to differentiate them.
+
+        By default, the flipped ports are given an 'in_' prefix and unflipped
+          ports keep their original names, enabling intuitive construction of
+          a device that will "plug into" the current device; the 'in_*' ports
+          are used for plugging the devices together while the original port
+          names are used for building the new device.
+
+        Another use-case could be to build the new device using the 'in_'
+          ports, creating a new device which could be used in place of the
+          current device.
+
+        Args:
+            name: Name for the new device
+            in_prefix: Prepended to port names for newly-created ports with
+                reversed directions compared to the current device.
+            out_prefix: Prepended to port names for ports which are directly
+                copied from the current device.
+            port_map: Specification for ports to copy into the new device:
+                - If `None`, all ports are copied.
+                - If a sequence, only the listed ports are copied
+                - If a mapping, the listed ports (keys) are copied and
+                    renamed (to the values).
+
+        Returns:
+            The new device, with an empty pattern and 2x as many ports as
+              listed in port_map.
+
+        Raises:
+            `DeviceError` if `port_map` contains port names not present in the
+                current device.
+            `DeviceError` if applying the prefixes results in duplicate port
+                names.
+        """
+        if port_map:
+            if isinstance(port_map, dict):
+                missing_inkeys = set(port_map.keys()) - set(self.ports.keys())
+                orig_ports = {port_map[k]: v for k, v in self.ports.items() if k in port_map}
+            else:
+                port_set = set(port_map)
+                missing_inkeys = port_set - set(self.ports.keys())
+                orig_ports = {k: v for k, v in self.ports.items() if k in port_set}
+
+            if missing_inkeys:
+                raise DeviceError(f'`port_map` keys not present in device: {missing_inkeys}')
+        else:
+            orig_ports = self.ports
+
+        ports_in = {f'{in_prefix}{name}': port.deepcopy().rotate(pi)
+                    for name, port in orig_ports.items()}
+        ports_out = {f'{out_prefix}{name}': port.deepcopy()
+                    for name, port in orig_ports.items()}
+
+        duplicates = set(ports_out.keys()) & set(ports_in.keys())
+        if duplicates:
+            raise DeviceError(f'Duplicate keys after prefixing, try a different prefix: {duplicates}')
+
+        new = Device(name=name, ports={**ports_in, **ports_out})
+        return new
+
+    def plug(self: D,
+             other: O,
+             map_in: Dict[str, str],
+             map_out: Optional[Dict[str, Optional[str]]] = None,
+             *,
+             mirrored: Tuple[bool, bool] = (False, False),
+             inherit_name: bool = True,
+             set_rotation: Optional[bool] = None,
+             ) -> D:
+        """
+        Instantiate the device `other` into the current device, connecting
+          the ports specified by `map_in` and renaming the unconnected
+          ports specified by `map_out`.
+
+        Examples:
+        =========
+        - `my_device.plug(subdevice, {'A': 'C', 'B': 'B'}, map_out={'D': 'myport'})`
+            instantiates `subdevice` into `my_device`, plugging ports 'A' and 'B'
+            of `my_device` into ports 'C' and 'B' of `subdevice`. The connected ports
+            are removed and any unconnected ports from `subdevice` are added to
+            `my_device`. Port 'D' of `subdevice` (unconnected) is renamed to 'myport'.
+
+        - `my_device.plug(wire, {'myport': 'A'})` places port 'A' of `wire` at 'myport'
+            of `my_device`. If `wire` has only two ports (e.g. 'A' and 'B'), no `map_out`,
+            argument is provided, and the `inherit_name` argument is not explicitly
+            set to `False`, the unconnected port of `wire` is automatically renamed to
+            'myport'. This allows easy extension of existing ports without changing
+            their names or having to provide `map_out` each time `plug` is called.
+
+        Args:
+            other: A device to instantiate into the current device.
+            map_in: Dict of `{'self_port': 'other_port'}` mappings, specifying
+                port connections between the two devices.
+            map_out: Dict of `{'old_name': 'new_name'}` mappings, specifying
+                new names for ports in `other`.
+            mirrored: Enables mirroring `other` across the x or y axes prior
+                to connecting any ports.
+            inherit_name: If `True`, and `map_in` specifies only a single port,
+                and `map_out` is `None`, and `other` has only two ports total,
+                then automatically renames the output port of `other` to the
+                name of the port from `self` that appears in `map_in`. This
+                makes it easy to extend a device with simple 2-port devices
+                (e.g. wires) without providing `map_out` each time `plug` is
+                called. See "Examples" above for more info. Default `True`.
+            set_rotation: If the necessary rotation cannot be determined from
+                the ports being connected (i.e. all pairs have at least one
+                port with `rotation=None`), `set_rotation` must be provided
+                to indicate how much `other` should be rotated. Otherwise,
+                `set_rotation` must remain `None`.
+
+        Returns:
+            self
+
+        Raises:
+            `DeviceError` if any ports specified in `map_in` or `map_out` do not
+                exist in `self.ports` or `other_names`.
+            `DeviceError` if there are any duplicate names after `map_in` and `map_out`
+                are applied.
+            `DeviceError` if the specified port mapping is not achieveable (the ports
+                do not line up)
+        """
+        if self._dead:
+            logger.error('Skipping plug() since device is dead')
+            return self
+
+        if (inherit_name
+                and not map_out
+                and len(map_in) == 1
+                and len(other.ports) == 2):
+            out_port_name = next(iter(set(other.ports.keys()) - set(map_in.values())))
+            map_out = {out_port_name: next(iter(map_in.keys()))}
+
+        if map_out is None:
+            map_out = {}
+        map_out = copy.deepcopy(map_out)
+
+        self.check_ports(other.ports.keys(), map_in, map_out)
+        translation, rotation, pivot = self.find_transform(other, map_in, mirrored=mirrored,
+                                                           set_rotation=set_rotation)
+
+        # get rid of plugged ports
+        for ki, vi in map_in.items():
+            del self.ports[ki]
+            map_out[vi] = None
+
+        self.place(other, offset=translation, rotation=rotation, pivot=pivot,
+                   mirrored=mirrored, port_map=map_out, skip_port_check=True)
+        return self
+
+    def place(self: D,
+              other: O,
+              *,
+              offset: vector2 = (0, 0),
+              rotation: float = 0,
+              pivot: vector2 = (0, 0),
+              mirrored: Tuple[bool, bool] = (False, False),
+              port_map: Optional[Dict[str, Optional[str]]] = None,
+              skip_port_check: bool = False,
+              ) -> D:
+        """
+        Instantiate the device `other` into the current device, adding its
+          ports to those of the current device (but not connecting any ports).
+
+        Mirroring is applied before rotation; translation (`offset`) is applied last.
+
+        Examples:
+        =========
+        - `my_device.place(pad, offset=(10, 10), rotation=pi / 2, port_map={'A': 'gnd'})`
+            instantiates `pad` at the specified (x, y) offset and with the specified
+            rotation, adding its ports to those of `my_device`. Port 'A' of `pad` is
+            renamed to 'gnd' so that further routing can use this signal or net name
+            rather than the port name on the original `pad` device.
+
+        Args:
+            other: A device to instantiate into the current device.
+            offset: Offset at which to place `other`. Default (0, 0).
+            rotation: Rotation applied to `other` before placement. Default 0.
+            pivot: Rotation is applied around this pivot point (default (0, 0)).
+                Rotation is applied prior to translation (`offset`).
+            mirrored: Whether `other` should be mirrored across the x and y axes.
+                Mirroring is applied before translation and rotation.
+            port_map: Dict of `{'old_name': 'new_name'}` mappings, specifying
+                new names for ports in `other`. New names can be `None`, which will
+                delete those ports.
+            skip_port_check: Can be used to skip the internal call to `check_ports`,
+                in case it has already been performed elsewhere.
+
+        Returns:
+            self
+
+        Raises:
+            `DeviceError` if any ports specified in `map_in` or `map_out` do not
+                exist in `self.ports` or `other_names`.
+            `DeviceError` if there are any duplicate names after `map_in` and `map_out`
+                are applied.
+        """
+        if self._dead:
+            logger.error('Skipping place() since device is dead')
+            return self
+
+        if port_map is None:
+            port_map = {}
+
+        if not skip_port_check:
+            self.check_ports(other.ports.keys(), map_in=None, map_out=port_map)
+
+        ports = {}
+        for name, port in other.ports.items():
+            new_name = port_map.get(name, name)
+            if new_name is None:
+                continue
+            ports[new_name] = port
+
+        for name, port in ports.items():
+            p = port.deepcopy()
+            p.mirror2d(mirrored)
+            p.rotate_around(pivot, rotation)
+            p.translate(offset)
+            self.ports[name] = p
+
+        sp = SubPattern(other.pattern, mirrored=mirrored)
+        sp.rotate_around(pivot, rotation)
+        sp.translate(offset)
+        self.pattern.subpatterns.append(sp)
+        return self
+
+    def find_transform(self: D,
+                       other: O,
+                       map_in: Dict[str, str],
+                       *,
+                       mirrored: Tuple[bool, bool] = (False, False),
+                       set_rotation: Optional[bool] = None,
+                       ) -> Tuple[numpy.ndarray, float, numpy.ndarray]:
+        """
+        Given a device `other` and a mapping `map_in` specifying port connections,
+          find the transform which will correctly align the specified ports.
+
+        Args:
+            other: a device
+            map_in: Dict of `{'self_port': 'other_port'}` mappings, specifying
+                port connections between the two devices.
+            mirrored: Mirrors `other` across the x or y axes prior to
+                connecting any ports.
+            set_rotation: If the necessary rotation cannot be determined from
+                the ports being connected (i.e. all pairs have at least one
+                port with `rotation=None`), `set_rotation` must be provided
+                to indicate how much `other` should be rotated. Otherwise,
+                `set_rotation` must remain `None`.
+
+        Returns:
+            - The (x, y) translation (performed last)
+            - The rotation (radians, counterclockwise)
+            - The (x, y) pivot point for the rotation
+
+            The rotation should be performed before the translation.
+        """
+        s_ports = self[map_in.keys()]
+        o_ports = other[map_in.values()]
+
+        s_offsets = numpy.array([p.offset for p in s_ports.values()])
+        o_offsets = numpy.array([p.offset for p in o_ports.values()])
+        s_types = numpy.array([p.ptype for p in s_ports.values()], dtype=int)
+        o_types = numpy.array([p.ptype for p in o_ports.values()], dtype=int)
+
+        s_rotations = numpy.array([p.rotation if p.rotation is not None else 0 for p in s_ports.values()])
+        o_rotations = numpy.array([p.rotation if p.rotation is not None else 0 for p in o_ports.values()])
+        s_has_rot = numpy.array([p.rotation is not None for p in s_ports.values()], dtype=bool)
+        o_has_rot = numpy.array([p.rotation is not None for p in o_ports.values()], dtype=bool)
+        has_rot = s_has_rot & o_has_rot
+
+        if mirrored[0]:
+            o_offsets[:, 1] *= -1
+            o_rotations *= -1
+        if mirrored[1]:
+            o_offsets[:, 0] *= -1
+            o_rotations *= -1
+            o_rotations += pi
+
+        type_conflicts = (s_types != o_types) & (s_types != 0) & (o_types != 0)
+        if type_conflicts.any():
+            ports = numpy.where(type_conflicts)
+            msg = 'Ports have conflicting types:\n'
+            for nn, (k, v) in enumerate(map_in.items()):
+                if type_conflicts[nn]:
+                    msg += f'{k} | {s_types[nn]:g}:{o_types[nn]:g} | {v}\n'
+            warnings.warn(msg, stacklevel=2)
+
+        rotations = numpy.mod(s_rotations - o_rotations - pi, 2 * pi)
+        if not has_rot.any():
+            if set_rotation is None:
+                DeviceError('Must provide set_rotation if rotation is indeterminate')
+            rotations[:] = set_rotation
+        else:
+            rotations[~has_rot] = rotations[has_rot][0]
+
+        if not numpy.allclose(rotations[:1], rotations):
+            rot_deg = numpy.rad2deg(rotations)
+            msg = f'Port orientations do not match:\n'
+            for nn, (k, v) in enumerate(map_in.items()):
+                msg += f'{k} | {rot_deg[nn]:g} | {v}\n'
+            raise DeviceError(msg)
+
+        pivot = o_offsets[0].copy()
+        rotate_offsets_around(o_offsets, pivot, rotations[0])
+        translations = s_offsets - o_offsets
+        if not numpy.allclose(translations[:1], translations):
+            msg = f'Port translations do not match:\n'
+            for nn, (k, v) in enumerate(map_in.items()):
+                msg += f'{k} | {translations[nn]} | {v}\n'
+            raise DeviceError(msg)
+
+        return translations[0], rotations[0], o_offsets[0]
+
+    def translate(self: D, offset: vector2) -> D:
+        """
+        Translate the pattern and all ports.
+
+        Args:
+            offset: (x, y) distance to translate by
+
+        Returns:
+            self
+        """
+        self.pattern.translate_elements(offset)
+        for port in self.ports.values():
+            port.translate(offset)
+        return self
+
+    def rotate_around(self: D, pivot: vector2, angle: float) -> D:
+        """
+        Translate the pattern and all ports.
+
+        Args:
+            offset: (x, y) distance to translate by
+
+        Returns:
+            self
+        """
+        self.pattern.rotate_around(pivot, angle)
+        for port in self.ports.values():
+            port.rotate_around(pivot, angle)
+        return self
+
+    def mirror(self: D, axis: int) -> D:
+        """
+        Translate the pattern and all ports across the specified axis.
+
+        Args:
+            axis: Axis to mirror across (x=0, y=1)
+
+        Returns:
+            self
+        """
+        self.pattern.mirror(axis)
+        for p in self.ports.values():
+            p.mirror(axis)
+        return self
+
+    def set_dead(self: D) -> D:
+        """
+        Disallows further changes through `plug()` or `place()`.
+        This is meant for debugging:
+        ```
+            dev.plug(a, ...)
+            dev.set_dead()      # added for debug purposes
+            dev.plug(b, ...)    # usually raises an error, but now skipped
+            dev.plug(c, ...)    # also skipped
+            dev.pattern.visualize()     # shows the device as of the set_dead() call
+        ```
+
+        Returns:
+            self
+        """
+        self._dead = True
+        return self
+
+    def __repr__(self) -> str:
+        s = f'<Device {self.pattern} ['
+        for name, port in self.ports.items():
+            s += f'\n\t{name}: {port}'
+        s += ']>'
+        return s
+
+
+def rotate_offsets_around(offsets: numpy.ndarray, pivot: numpy.ndarray, angle: float) -> numpy.ndarray:
+    offsets -= pivot
+    offsets[:] = (rotation_matrix_2d(angle) @ offsets.T).T
+    offsets += pivot
+    return offsets
diff --git a/masque/builder/utils.py b/masque/builder/utils.py
new file mode 100644
index 0000000..d4a9dbe
--- /dev/null
+++ b/masque/builder/utils.py
@@ -0,0 +1,189 @@
+from typing import Dict, Tuple, List, Optional, Union, Any, cast, Sequence
+from pprint import pformat
+
+import numpy        # type: ignore
+from numpy import pi
+
+from .devices import Port
+from ..utils import rotation_matrix_2d, vector2
+from ..error import BuildError
+
+
+def ell(ports: Dict[str, Port],
+        ccw: Optional[bool],
+        bound_type: str,
+        bound: Union[float, vector2],
+        *,
+        spacing: Optional[Union[float, numpy.ndarray]] = None,
+        set_rotation: Optional[float] = None,
+        ) -> Dict[str, float]:
+    """
+    Calculate extension for each port in order to build a 90-degree bend with the provided
+    channel spacing:
+
+         =A>---------------------------V     turn direction: `ccw=False`
+                   =B>-------------V   |
+     =C>-----------------------V   |   |
+       =D=>----------------V   |   |   |
+
+
+                           x---x---x---x  `spacing` (can be scalar or array)
+
+                    <-------------->      `bound_type='min_extension'`
+                    <------>                         `'min_past_furthest'`
+      <-------------------------------->             `'max_extension'`
+                           x                         `'min_position'`
+                                       x             `'max_position'`
+
+    Args:
+        ports: `name: port` mapping. All ports should have the same rotation (or `None`). If
+            no port has a rotation specified, `set_rotation` must be provided.
+        ccw: Turn direction. `True` means counterclockwise, `False` means clockwise,
+            and `None` means no bend. If `None`, spacing must remain `None` or `0` (default),
+            Otherwise, spacing must be set to a non-`None` value.
+        bound_method: Method used for determining the travel distance; see diagram above.
+            Valid values are:
+            - 'min_extension' or 'emin':
+                The total extension value for the furthest-out port (B in the diagram).
+            - 'min_past_furthest':
+                The distance between furthest out-port (B) and the innermost bend (D's bend).
+            - 'max_extension' or 'emax':
+                The total extension value for the closest-in port (C in the diagram).
+            - 'min_position' or 'pmin':
+                The coordinate of the innermost bend (D's bend).
+            - 'max_position' or 'pmax':
+                The coordinate of the outermost bend (A's bend).
+
+            `bound` can also be a vector. If specifying an extension (e.g. 'min_extension',
+                'max_extension', 'min_past_furthest'), it sets independent limits along
+                the x- and y- axes. If specifying a position, it is projected onto
+                the extension direction.
+
+        bound_value: Value associated with `bound_type`, see above.
+        spacing: Distance between adjacent channels. Can be scalar, resulting in evenly
+            spaced channels, or a vector with length one less than `ports`, allowing
+            non-uniform spacing.
+            The ordering of the vector corresponds to the output order (DCBA in the
+            diagram above), *not* the order of `ports`.
+        set_rotation: If all ports have no specified rotation, this value is used
+            to set the extension direction. Otherwise it must remain `None`.
+
+    Returns:
+        Dict of {port_name: distance_to_bend}
+
+    Raises:
+        `BuildError` on bad inputs
+        `BuildError` if the requested bound is impossible
+    """
+    if not ports:
+        raise BuildError('Empty port list passed to `ell()`')
+
+    if ccw is None:
+        if spacing is not None and not numpy.isclose(spacing, 0):
+            raise BuildError('Spacing must be 0 or None when ccw=None')
+        spacing = 0
+    elif spacing is None:
+        raise BuildError('Must provide spacing if a bend direction is specified')
+
+    has_rotation = numpy.array([p.rotation is not None for p in ports.values()], dtype=bool)
+    if has_rotation.any():
+        if set_rotation is not None:
+            raise BuildError('set_rotation must be None when ports have rotations!')
+
+        rotations = numpy.array([p.rotation if p.rotation is not None else 0
+                                 for p in ports.values()])
+        rotations[~has_rotation] = rotations[has_rotation][0]
+
+        if not numpy.allclose(rotations[0], rotations):
+            raise BuildError('Asked to find aggregation for ports that face in different directions:\n'
+                             + pformat({k: numpy.rad2deg(p.rotation) for k, p in ports.items()}))
+    else:
+        if set_rotation is not None:
+            raise BuildError('set_rotation must be specified if no ports have rotations!')
+        rotations = numpy.full_like(has_rotation, set_rotation, dtype=float)
+
+    direction = rotations[0] + pi                        # direction we want to travel in (+pi relative to port)
+    rot_matrix = rotation_matrix_2d(-direction)
+
+    # Rotate so are traveling in +x
+    orig_offsets = numpy.array([p.offset for p in ports.values()])
+    rot_offsets = (rot_matrix @ orig_offsets.T).T
+
+    y_order = ((-1 if ccw else 1) * rot_offsets[:, 1]).argsort()
+    y_ind = numpy.empty_like(y_order, dtype=int)
+    y_ind[y_order] = numpy.arange(y_ind.shape[0])
+
+    if spacing is None:
+        ch_offsets = numpy.zeros_like(y_order)
+    else:
+        steps = numpy.zeros_like(y_order)
+        steps[1:] = spacing
+        ch_offsets = numpy.cumsum(steps)[y_ind]
+
+    x_start = rot_offsets[:, 0]
+
+    #     A---------|  `d_to_align[0]`
+    #               B  `d_to_align[1]`
+    # C-------------|  `d_to_align[2]`
+    #   D-----------|  `d_to_align[3]`
+    #
+    d_to_align = x_start.max() - x_start    # distance to travel to align all
+    if bound_type == 'min_past_furthest':
+        #     A------------------V  `d_to_exit[0]`
+        #               B-----V     `d_to_exit[1]`
+        # C----------------V        `d_to_exit[2]`
+        #   D-----------V           `d_to_exit[3]`
+        offsets = d_to_align + ch_offsets
+    else:
+        #     A---------V  `travel[0]`   <-- Outermost port aligned to furthest-x port
+        #            V--B  `travel[1]`   <-- Remaining ports follow spacing
+        # C-------V        `travel[2]`
+        #   D--V           `travel[3]`
+        #
+        #     A------------V  `offsets[0]`
+        #               B     `offsets[1]`   <-- Travels adjusted to be non-negative
+        # C----------V        `offsets[2]`
+        #   D-----V           `offsets[3]`
+        travel = d_to_align - (ch_offsets.max() - ch_offsets)
+        offsets = travel - travel.min().clip(max=0)
+
+    if bound_type in ('emin', 'min_extension',
+                      'emax', 'max_extension',
+                      'min_past_furthest',):
+        if numpy.size(bound) == 2:
+            bound = cast(Sequence[float], bound)
+            rot_bound = (rot_matrix @ ((bound[0], 0),
+                                       (0, bound[1])))[0, :]
+        else:
+            bound = cast(float, bound)
+            rot_bound = numpy.array(bound)
+
+        if rot_bound < 0:
+            raise BuildError(f'Got negative bound for extension: {rot_bound}')
+
+        if bound_type in ('emin', 'min_extension', 'min_past_furthest'):
+            offsets += rot_bound.max()
+        elif bound_type in('emax', 'max_extension'):
+            offsets += rot_bound.min() - offsets.max()
+    else:
+        if numpy.size(bound) == 2:
+            bound = cast(Sequence[float], bound)
+            rot_bound = (rot_matrix @ bound)[0]
+        else:
+            bound = cast(float, bound)
+            neg = (direction + pi / 4) % (2 * pi) > pi
+            rot_bound = -bound if neg else bound
+
+        min_possible = x_start + offsets
+        if bound_type in ('pmax', 'max_position'):
+            extension = rot_bound - min_possible.max()
+        elif bound_type in ('pmin', 'min_position'):
+            extension = rot_bound - min_possible.min()
+
+        offsets += extension
+        if extension < 0:
+            raise BuildError(f'Position is too close by at least {-numpy.floor(extension)}. Total extensions would be'
+                            + '\n\t'.join(f'{key}: {off}' for key, off in zip(ports.keys(), offsets)))
+
+    result = dict(zip(ports.keys(), offsets))
+    return result
diff --git a/masque/error.py b/masque/error.py
index e109c20..84607b7 100644
--- a/masque/error.py
+++ b/masque/error.py
@@ -1,13 +1,15 @@
-class PatternError(Exception):
+class MasqueError(Exception):
     """
-    Simple Exception for Pattern objects and their contents
+    Parent exception for all Masque-related Exceptions
     """
-    def __init__(self, value):
-        self.value = value
+    pass
 
-    def __str__(self):
-        return repr(self.value)
 
+class PatternError(MasqueError):
+    """
+    Exception for Pattern objects and their contents
+    """
+    pass
 
 class PatternLockedError(PatternError):
     """
@@ -17,10 +19,22 @@ class PatternLockedError(PatternError):
         PatternError.__init__(self, 'Tried to modify a locked Pattern, subpattern, or shape')
 
 
-class LibraryError(Exception):
+class LibraryError(MasqueError):
     """
     Exception raised by Library classes
     """
     pass
 
 
+class DeviceError(MasqueError):
+    """
+    Exception raised by Device and Port objects
+    """
+    pass
+
+
+class BuildError(MasqueError):
+    """
+    Exception raised by builder-related functions
+    """
+    pass
diff --git a/masque/file/dxf.py b/masque/file/dxf.py
index 906fc2f..f99455b 100644
--- a/masque/file/dxf.py
+++ b/masque/file/dxf.py
@@ -70,7 +70,7 @@ def write(pattern: Pattern,
     """
     #TODO consider supporting DXF arcs?
     if disambiguate_func is None:
-        disambiguate_func = disambiguate_pattern_names
+        disambiguate_func = lambda pats: disambiguate_pattern_names(pats)
     assert(disambiguate_func is not None)
 
     if not modify_originals:
@@ -349,7 +349,7 @@ def _mlayer2dxf(layer: layer_t) -> str:
     raise PatternError(f'Unknown layer type: {layer} ({type(layer)})')
 
 
-def disambiguate_pattern_names(patterns: Sequence[Pattern],
+def disambiguate_pattern_names(patterns: Iterable[Pattern],
                                max_name_length: int = 32,
                                suffix_length: int = 6,
                                dup_warn_filter: Callable[[str], bool] = None,      # If returns False, don't warn about this name
diff --git a/masque/file/klamath.py b/masque/file/klamath.py
index 0f858cf..e7015be 100644
--- a/masque/file/klamath.py
+++ b/masque/file/klamath.py
@@ -188,6 +188,7 @@ def readfile(filename: Union[str, pathlib.Path],
 
 
 def read(stream: BinaryIO,
+         raw_mode: bool = True,
          ) -> Tuple[Dict[str, Pattern], Dict[str, Any]]:
     """
     Read a gdsii file and translate it into a dict of Pattern objects. GDSII structures are
@@ -202,12 +203,12 @@ def read(stream: BinaryIO,
 
     Args:
         stream: Stream to read from.
+        raw_mode: If True, constructs shapes in raw mode, bypassing most data validation, Default True.
 
     Returns:
         - Dict of pattern_name:Patterns generated from GDSII structures
         - Dict of GDSII library info
     """
-    raw_mode = True     # Whether to construct shapes in raw mode (less error checking)
     library_info = _read_header(stream)
 
     patterns = []
@@ -253,7 +254,7 @@ def read_elements(stream: BinaryIO,
         stream: Seekable stream, positioned at a record boundary.
                 Will be read until an ENDSTR record is consumed.
         name: Name of the resulting Pattern
-        raw_mode: If True, bypass per-shape consistency checking
+        raw_mode: If True, bypass per-shape data validation. Default True.
 
     Returns:
         A pattern containing the elements that were read.
@@ -551,6 +552,8 @@ def disambiguate_pattern_names(patterns: Sequence[Pattern],
 def load_library(stream: BinaryIO,
                  tag: str,
                  is_secondary: Optional[Callable[[str], bool]] = None,
+                 *,
+                 full_load: bool = False,
                  ) -> Tuple[Library, Dict[str, Any]]:
     """
     Scan a GDSII stream to determine what structures are present, and create
@@ -568,6 +571,10 @@ def load_library(stream: BinaryIO,
                       True if the structure should only be used as a subcell
                       and not appear in the main Library interface.
                       Default always returns False.
+        full_load: If True, force all structures to be read immediately rather
+                   than as-needed. Since data is read sequentially from the file,
+                   this will be faster than using the resulting library's
+                   `precache` method.
 
     Returns:
         Library object, allowing for deferred load of structures.
@@ -576,12 +583,22 @@ def load_library(stream: BinaryIO,
     if is_secondary is None:
         def is_secondary(k: str):
             return False
+    assert(is_secondary is not None)
 
     stream.seek(0)
+    lib = Library()
+
+    if full_load:
+        # Full load approach (immediately load everything)
+        patterns, library_info = read(stream)
+        for name, pattern in patterns.items():
+            lib.set_const(name, tag, pattern, secondary=is_secondary(name))
+        return lib, library_info
+
+    # Normal approach (scan and defer load)
     library_info = _read_header(stream)
     structs = klamath.library.scan_structs(stream)
 
-    lib = Library()
     for name_bytes, pos in structs.items():
         name = name_bytes.decode('ASCII')
 
@@ -597,7 +614,9 @@ def load_library(stream: BinaryIO,
 def load_libraryfile(filename: Union[str, pathlib.Path],
                      tag: str,
                      is_secondary: Optional[Callable[[str], bool]] = None,
+                     *,
                      use_mmap: bool = True,
+                     full_load: bool = False,
                      ) -> Tuple[Library, Dict[str, Any]]:
     """
     Wrapper for `load_library()` that takes a filename or path instead of a stream.
@@ -615,6 +634,7 @@ def load_libraryfile(filename: Union[str, pathlib.Path],
                   of buffering. In the case of gzipped files, the file
                   is decompressed into a python `bytes` object in memory
                   and reopened as an `io.BytesIO` stream.
+        full_load: If `True`, immediately loads all data. See `load_library`.
 
     Returns:
         Library object, allowing for deferred load of structures.
diff --git a/masque/file/oasis.py b/masque/file/oasis.py
index dea703d..92abbfd 100644
--- a/masque/file/oasis.py
+++ b/masque/file/oasis.py
@@ -674,7 +674,7 @@ def annotations_to_properties(annotations: annotations_t) -> List[fatrec.Propert
     for key, values in annotations.items():
         vals = [AString(v) if isinstance(v, str) else v
                 for v in values]
-        properties.append(fatrec.Property(key, vals, is_standard=False))
+        properties.append(fatrec.Property(key, vals, is_standard=False))        # type: ignore
     return properties
 
 
diff --git a/masque/label.py b/masque/label.py
index b436653..d71d69c 100644
--- a/masque/label.py
+++ b/masque/label.py
@@ -58,11 +58,11 @@ class Label(PositionableImpl, LayerableImpl, LockableImpl, RepeatableImpl, Annot
         self.set_locked(locked)
 
     def __copy__(self: L) -> L:
-        return Label(string=self.string,
-                     offset=self.offset.copy(),
-                     layer=self.layer,
-                     repetition=self.repetition,
-                     locked=self.locked)
+        return type(self)(string=self.string,
+                          offset=self.offset.copy(),
+                          layer=self.layer,
+                          repetition=self.repetition,
+                          locked=self.locked)
 
     def __deepcopy__(self: L, memo: Dict = None) -> L:
         memo = {} if memo is None else memo
diff --git a/masque/library/__init__.py b/masque/library/__init__.py
index a72f3b9..0d40b3b 100644
--- a/masque/library/__init__.py
+++ b/masque/library/__init__.py
@@ -1 +1,2 @@
 from .library import Library, PatternGenerator
+from .device_library import DeviceLibrary
diff --git a/masque/library/device_library.py b/masque/library/device_library.py
new file mode 100644
index 0000000..cf06e72
--- /dev/null
+++ b/masque/library/device_library.py
@@ -0,0 +1,105 @@
+"""
+DeviceLibrary class for managing unique name->device mappings and
+ deferred loading or creation.
+"""
+from typing import Dict, Callable, TypeVar, TYPE_CHECKING
+from typing import Any, Tuple, Union, Iterator
+import logging
+from pprint import pformat
+
+from ..error import LibraryError
+
+if TYPE_CHECKING:
+    from ..builder import Device
+
+
+logger = logging.getLogger(__name__)
+
+
+L = TypeVar('L', bound='DeviceLibrary')
+
+
+class DeviceLibrary:
+    """
+    This class is usually used to create a device library by mapping names to
+     functions which generate or load the relevant `Device` object as-needed.
+
+    The cache can be disabled by setting the `enable_cache` attribute to `False`.
+    """
+    generators: Dict[str, Callable[[], 'Device']]
+    cache: Dict[Union[str, Tuple[str, str]], 'Device']
+    enable_cache: bool = True
+
+    def __init__(self) -> None:
+        self.generators = {}
+        self.cache = {}
+
+    def __setitem__(self, key: str, value: Callable[[], 'Device']) -> None:
+        self.generators[key] = value
+        if key in self.cache:
+            del self.cache[key]
+
+    def __delitem__(self, key: str) -> None:
+        del self.generators[key]
+        if key in self.cache:
+            del self.cache[key]
+
+    def __getitem__(self, key: str) -> 'Device':
+        if self.enable_cache and key in self.cache:
+            logger.debug(f'found {key} in cache')
+            return self.cache[key]
+
+        logger.debug(f'loading {key}')
+        dev = self.generators[key]()
+        self.cache[key] = dev
+        return dev
+
+    def __iter__(self) -> Iterator[str]:
+        return iter(self.keys())
+
+    def __contains__(self, key: str) -> bool:
+        return key in self.generators
+
+    def keys(self) -> Iterator[str]:
+        return iter(self.generators.keys())
+
+    def values(self) -> Iterator['Device']:
+        return iter(self[key] for key in self.keys())
+
+    def items(self) -> Iterator[Tuple[str, 'Device']]:
+        return iter((key, self[key]) for key in self.keys())
+
+    def __repr__(self) -> str:
+        return '<DeviceLibrary with keys ' + repr(list(self.generators.keys())) + '>'
+
+    def set_const(self, key: str, const: 'Device') -> None:
+        """
+        Convenience function to avoid having to manually wrap
+         constant values into callables.
+
+        Args:
+            key: Lookup key, usually the device name
+            const: Device object to return
+        """
+        self.generators[key] = lambda: const
+
+    def add(self: L, other: L) -> L:
+        """
+        Add keys from another library into this one.
+
+        There must be no conflicting keys.
+
+        Args:
+            other: The library to insert keys from
+
+        Returns:
+            self
+        """
+        conflicts = [key for key in other.generators
+                     if key in self.generators]
+        if conflicts:
+            raise LibraryError('Duplicate keys encountered in library merge: ' + pformat(conflicts))
+
+        self.generators.update(other.generators)
+        self.cache.update(other.cache)
+        return self
diff --git a/masque/pattern.py b/masque/pattern.py
index 55c9ab7..7cbd06d 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -2,7 +2,7 @@
  Base object representing a lithography mask.
 """
 
-from typing import List, Callable, Tuple, Dict, Union, Set, Sequence, Optional, Type, overload
+from typing import List, Callable, Tuple, Dict, Union, Set, Sequence, Optional, Type, overload, cast
 from typing import MutableMapping, Iterable, TypeVar, Any
 import copy
 import pickle
@@ -18,7 +18,8 @@ from .shapes import Shape, Polygon
 from .label import Label
 from .utils import rotation_matrix_2d, vector2, normalize_mirror, AutoSlots, annotations_t
 from .error import PatternError, PatternLockedError
-from .traits import LockableImpl, AnnotatableImpl, Scalable
+from .traits import LockableImpl, AnnotatableImpl, Scalable, Mirrorable
+from .traits import Rotatable, Positionable
 
 
 visitor_function_t = Callable[['Pattern', Tuple['Pattern'], Dict, numpy.ndarray], 'Pattern']
@@ -27,7 +28,7 @@ visitor_function_t = Callable[['Pattern', Tuple['Pattern'], Dict, numpy.ndarray]
 P = TypeVar('P', bound='Pattern')
 
 
-class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
+class Pattern(LockableImpl, AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
     """
     2D layout consisting of some set of shapes, labels, and references to other Pattern objects
      (via SubPattern). Shapes are assumed to inherit from masque.shapes.Shape or provide equivalent functions.
@@ -91,7 +92,7 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
         self.name = name
         self.set_locked(locked)
 
-    def __copy__(self: P, memo: Dict = None) -> P:
+    def __copy__(self, memo: Dict = None) -> 'Pattern':
         return Pattern(name=self.name,
                        shapes=copy.deepcopy(self.shapes),
                        labels=copy.deepcopy(self.labels),
@@ -99,7 +100,7 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
                        annotations=copy.deepcopy(self.annotations),
                        locked=self.locked)
 
-    def __deepcopy__(self: P, memo: Dict = None) -> P:
+    def __deepcopy__(self, memo: Dict = None) -> 'Pattern':
         memo = {} if memo is None else memo
         new = Pattern(
             name=self.name,
@@ -130,12 +131,12 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
         self.labels += other_pattern.labels
         return self
 
-    def subset(self: P,
+    def subset(self,
                shapes_func: Callable[[Shape], bool] = None,
                labels_func: Callable[[Label], bool] = None,
                subpatterns_func: Callable[[SubPattern], bool] = None,
                recursive: bool = False,
-               ) -> P:
+               ) -> 'Pattern':
         """
         Returns a Pattern containing only the entities (e.g. shapes) for which the
           given entity_func returns True.
@@ -155,7 +156,7 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
             A Pattern containing all the shapes and subpatterns for which the parameter
                 functions return True
         """
-        def do_subset(src: Optional[P]) -> Optional[P]:
+        def do_subset(src: Optional['Pattern']) -> Optional['Pattern']:
             if src is None:
                 return None
             pat = Pattern(name=src.name)
@@ -175,10 +176,10 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
         assert(pat is not None)
         return pat
 
-    def apply(self: P,
-              func: Callable[[Optional[P]], Optional[P]],
-              memo: Optional[Dict[int, Optional[P]]] = None,
-              ) -> Optional[P]:
+    def apply(self,
+              func: Callable[[Optional['Pattern']], Optional['Pattern']],
+              memo: Optional[Dict[int, Optional['Pattern']]] = None,
+              ) -> Optional['Pattern']:
         """
         Recursively apply func() to this pattern and any pattern it references.
         func() is expected to take and return a Pattern.
@@ -473,7 +474,7 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
                 ids.update(pat.referenced_patterns_by_id())
         return ids
 
-    def referenced_patterns_by_name(self, **kwargs) -> List[Tuple[Optional[str], Optional['Pattern']]]:
+    def referenced_patterns_by_name(self, **kwargs: Any) -> List[Tuple[Optional[str], Optional['Pattern']]]:
         """
         Create a list of `(pat.name, pat)` tuples for all Pattern objects referenced by this
          Pattern (operates recursively on all referenced Patterns as well).
@@ -710,7 +711,7 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
             self
         """
         for entry in chain(self.shapes, self.subpatterns):
-            entry.rotate(rotation)
+            cast(Rotatable, entry).rotate(rotation)
         return self
 
     def mirror_element_centers(self: P, axis: int) -> P:
@@ -741,7 +742,7 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
             self
         """
         for entry in chain(self.shapes, self.subpatterns):
-            entry.mirror(axis)
+            cast(Mirrorable, entry).mirror(axis)
         return self
 
     def mirror(self: P, axis: int) -> P:
@@ -803,14 +804,14 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
                 and len(self.shapes) == 0
                 and len(self.labels) == 0)
 
-    def addsp(self, *args: Dict[str, Any], **kwargs: Dict[str, Any]):
+    def addsp(self: P, *args: Any, **kwargs: Any) -> P:
         """
         Convenience function which constructs a subpattern object and adds it
          to this pattern.
 
         Args:
-            *args: Passed to SubPattern()
-            **kwargs: Passed to SubPattern()
+            *args: Passed to `SubPattern()`
+            **kwargs: Passed to `SubPattern()`
 
         Returns:
             self
@@ -856,7 +857,7 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
         """
         self.lock()
         for ss in chain(self.shapes, self.labels):
-            ss.lock()
+            ss.lock()       # type: ignore      # mypy struggles with multiple inheritance :(
         for sp in self.subpatterns:
             sp.deeplock()
         return self
@@ -873,7 +874,7 @@ class Pattern(LockableImpl, AnnotatableImpl, metaclass=AutoSlots):
         """
         self.unlock()
         for ss in chain(self.shapes, self.labels):
-            ss.unlock()
+            ss.unlock()       # type: ignore      # mypy struggles with multiple inheritance :(
         for sp in self.subpatterns:
             sp.deepunlock()
         return self
diff --git a/masque/shapes/arc.py b/masque/shapes/arc.py
index 0416d01..f4542c4 100644
--- a/masque/shapes/arc.py
+++ b/masque/shapes/arc.py
@@ -236,12 +236,16 @@ class Arc(Shape, metaclass=AutoSlots):
         if poly_max_arclen is not None:
             n += [perimeter / poly_max_arclen]
         num_points = int(round(max(n)))
-        thetas_inner = numpy.linspace(a_ranges[0][1], a_ranges[0][0], num_points, endpoint=True)
+
+        wh = self.width / 2.0
+        if wh == r0 and r0 == r1:
+            thetas_inner = [0]      # Don't generate multiple vertices if we're at the origin
+        else:
+            thetas_inner = numpy.linspace(a_ranges[0][1], a_ranges[0][0], num_points, endpoint=True)
         thetas_outer = numpy.linspace(a_ranges[1][0], a_ranges[1][1], num_points, endpoint=True)
 
         sin_th_i, cos_th_i = (numpy.sin(thetas_inner), numpy.cos(thetas_inner))
         sin_th_o, cos_th_o = (numpy.sin(thetas_outer), numpy.cos(thetas_outer))
-        wh = self.width / 2.0
 
         xs1 = (r0 + wh) * cos_th_o
         ys1 = (r1 + wh) * sin_th_o
@@ -326,6 +330,7 @@ class Arc(Shape, metaclass=AutoSlots):
     def mirror(self, axis: int) -> 'Arc':
         self.offset[axis - 1] *= -1
         self.rotation *= -1
+        self.rotation += axis * pi
         self.angles *= -1
         return self
 
diff --git a/masque/shapes/ellipse.py b/masque/shapes/ellipse.py
index 140f590..f9aefbf 100644
--- a/masque/shapes/ellipse.py
+++ b/masque/shapes/ellipse.py
@@ -183,6 +183,7 @@ class Ellipse(Shape, metaclass=AutoSlots):
     def mirror(self, axis: int) -> 'Ellipse':
         self.offset[axis - 1] *= -1
         self.rotation *= -1
+        self.rotation += axis * pi
         return self
 
     def scale_by(self, c: float) -> 'Ellipse':
diff --git a/masque/shapes/polygon.py b/masque/shapes/polygon.py
index 59ab82d..7c48be3 100644
--- a/masque/shapes/polygon.py
+++ b/masque/shapes/polygon.py
@@ -269,6 +269,64 @@ class Polygon(Shape, metaclass=AutoSlots):
                                  layer=layer, dose=dose)
         return poly
 
+    @staticmethod
+    def octagon(*,
+                side_length: Optional[float] = None,
+                inner_radius: Optional[float] = None,
+                regular: bool = True,
+                center: vector2 = (0.0, 0.0),
+                rotation: float = 0.0,
+                layer: layer_t = 0,
+                dose: float = 1.0,
+                ) -> 'Polygon':
+        """
+        Draw an octagon given one of (side length, inradius, circumradius).
+
+        Args:
+            side_length: Length of one side. For an irregular octagon, this
+                specifies the length of the long sides.
+            inner_radius: Half of distance between opposite sides. For an irregular
+                octagon, this specifies the spacing between the long sides.
+            regular: If `True`, all sides have the same length. If `False`,
+                a "clipped square" with vertices (+-1, +-2) and (+-2, +-1)
+                is generated, avoiding irrational coordinate locations and
+                guaranteeing 45 degree edges.
+            center: Offset, default `(0, 0)`
+            rotation: Rotation counterclockwise, in radians.
+                `0` results in four axis-aligned sides (the long sides of the
+                irregular octagon).
+            layer: Layer, default `0`
+            dose: Dose, default `1.0`
+
+        Returns:
+            A Polygon object containing the requested octagon
+        """
+        if regular:
+            s = 1 + numpy.sqrt(2)
+        else:
+            s = 2
+
+        norm_oct = numpy.array([
+            [-1, -s],
+            [-s, -1],
+            [-s,  1],
+            [-1,  s],
+            [ 1,  s],
+            [ s,  1],
+            [ s, -1],
+            [ 1, -s]], dtype=float)
+
+        if side_length is None:
+            if inner_radius is None:
+                raise PatternError('One of `side_length` or `inner_radius` must be specified.')
+            side_length = 2 * inner_radius / s
+
+        vertices = 0.5 * side_length * norm_oct
+        poly = Polygon(vertices, offset=center, layer=layer, dose=dose)
+        poly.rotate(rotation)
+        return poly
+
+
     def to_polygons(self,
                     poly_num_points: int = None,        # unused
                     poly_max_arclen: float = None,      # unused
diff --git a/masque/shapes/text.py b/masque/shapes/text.py
index 07cc1a7..d6cb3ac 100644
--- a/masque/shapes/text.py
+++ b/masque/shapes/text.py
@@ -121,7 +121,7 @@ class Text(RotatableImpl, Shape, metaclass=AutoSlots):
             # Move these polygons to the right of the previous letter
             for xys in raw_polys:
                 poly = Polygon(xys, dose=self.dose, layer=self.layer)
-                [poly.mirror(ax) for ax, do in enumerate(self.mirrored) if do]
+                poly.mirror2d(self.mirrored)
                 poly.scale_by(self.height)
                 poly.offset = self.offset + [total_advance, 0]
                 poly.rotate_around(self.offset, self.rotation)
diff --git a/masque/snaps/snapper.py b/masque/snaps/snapper.py
deleted file mode 100644
index 190ba55..0000000
--- a/masque/snaps/snapper.py
+++ /dev/null
@@ -1,121 +0,0 @@
-
-
-callback_t = Callable[[T, numpy.ndarray, Dict[str, int]], ...]
-
-
-class Device:
-    pattern: Pattern
-    ports: numpy.ndarray
-    port_names: Dict[str, int]
-    callback: Optional[callback_t] = None
-
-    def __init__(self,
-                 pattern: Optional[Pattern] = None,
-                 ports: Optional[numpy.ndarray] = None,
-                 names: Optional[Union[Dict[str, int], List[Optional[str]]] = None,
-                 callback: Optional[callback_t]= None
-                 ) -> None:
-        if pattern is None:
-            self.pattern = Pattern()
-
-        if ports is None:
-            self.ports = {0: [0, 0,  0, 0],
-                          1: [0, 0, pi, 0]}
-        else:
-            self.ports = numpy.array(ports)
-
-        if callback:
-            self.callback = callback
-            self.callback(self, self.ports.keys())
-
-    def __getitem__(self, key) -> numpy.ndarray:
-        if isinstance(key, str):
-            inds = [self.port_names[key]]
-        elif hasattr(key, '__iter__'):
-            inds = [self.port_names.get(k, k) for k in key]
-        else:
-            inds = [self.port_names.get(key, key)]
-        return self.ports[inds]
-
-    def build(self: T,
-              name: str,
-              other: Device,
-              map_in: Dict[port_t, port_t],
-              map_out: Dict[port_t, port_t],
-              mirror: bool = False,
-              ) -> T:
-        translation, rotation = self.find_transform(other, map_in, map_out, mirror)
-
-        pat = Pattern(name)
-        pat.addsp(self.pattern)
-        new = Device(pat, ports=self.ports, port_names=self.port_names, callback=self.callback)
-        return new
-
-
-    def plug(self, other, map_in, map_out, mirror):
-        translation, rotation, pivot = self.find_transform(other, map_in, map_out, mirror)
-
-        sp = SubPattern(other.pattern, mirrored=mirror)
-        sp.rotate_around(pivot, rotation)
-        sp.translate(translation)
-        self.pat.subpatterns.append(sp)
-
-        # get rid of plugged ports
-
-        # insert remaining device ports into router port list
-
-        with numpy.errstate(invalid='ignore'):
-            self.ports[:, 2] %= 2 * pi
-
-        if self.port_callback:
-            self.port_callback(...)
-
-    def find_transform(self, other, map_in, map_out, mirror):
-        s_ports = self[map_in.keys()]
-        o_ports= other[map_in.values()]
-
-        if mirror[0]:
-            o_ports[:, 1] *= -1
-            o_ports[:, 2] += pi
-        if mirror[1]:
-            o_ports[:, 0] *= -1
-            o_ports[:, 2] += pi
-
-        s_offsets = s_ports[:, :2]
-        s_angles = s_ports[:, 2]
-        s_types = s_ports[:, 3]
-        o_offsets = o_ports[:, :2]
-        o_angles = o_ports[:, 2]
-        o_types = o_ports[:, 3]
-
-        if (r_types != d_types) & (r_types != 0) & (d_types != 0):
-            #TODO warn about types
-
-        rotations = numpy.mod(s_angles - o_angles - pi, 2 * pi)
-
-        if not numpy.allclose(rotations[:1], rotations):
-            # TODO warn about rotation
-
-        rot_ports = rotate_ports_around(o_ports, o_offsets[0], rotations[0])       #TODO also rotate unplugged device ports
-
-        translations = r_offsets - d_offsets
-        translation = translations[0]
-
-        if not numpy.allclose(translations[:1], translations):
-
-        return translations[0], rotations[0]
-
-
-    def as_pattern(self, name) -> Pattern:
-        return self.pat.copy().rename(name)
-
-    def as_device(self, name):
-        return Device(self.as_pattern, REMAINING_NON-NAN_PORTS) #TODO
-
-
-def rotate_ports_around(ports: numpy.ndarray, pivot: numpy.ndarray, angle: float) -> numpy.ndarray:
-    ports[:, :2] -= pivot
-    ports[:, :2] = (rotation_matrix_2d(angle) @ ports[:, :2].T).T
-    ports[:, :2] += pivot
-    ports[:, 2] += angle
-    return ports
diff --git a/masque/subpattern.py b/masque/subpattern.py
index 9d04b89..3913b33 100644
--- a/masque/subpattern.py
+++ b/masque/subpattern.py
@@ -79,13 +79,13 @@ class SubPattern(PositionableImpl, DoseableImpl, RotatableImpl, ScalableImpl, Mi
         self.dose = dose
         self.scale = scale
         if mirrored is None:
-            mirrored = [False, False]
+            mirrored = (False, False)
         self.mirrored = mirrored
         self.repetition = repetition
         self.annotations = annotations if annotations is not None else {}
         self.set_locked(locked)
 
-    def __copy__(self: S) -> S:
+    def __copy__(self) -> 'SubPattern':
         new = SubPattern(pattern=self.pattern,
                          offset=self.offset.copy(),
                          rotation=self.rotation,
@@ -97,7 +97,7 @@ class SubPattern(PositionableImpl, DoseableImpl, RotatableImpl, ScalableImpl, Mi
                          locked=self.locked)
         return new
 
-    def __deepcopy__(self: S, memo: Dict = None) -> S:
+    def __deepcopy__(self, memo: Dict = None) -> 'SubPattern':
         memo = {} if memo is None else memo
         new = copy.copy(self).unlock()
         new.pattern = copy.deepcopy(self.pattern, memo)
@@ -138,7 +138,7 @@ class SubPattern(PositionableImpl, DoseableImpl, RotatableImpl, ScalableImpl, Mi
         assert(self.pattern is not None)
         pattern = self.pattern.deepcopy().deepunlock()
         pattern.scale_by(self.scale)
-        [pattern.mirror(ax) for ax, do in enumerate(self.mirrored) if do]
+        pattern.mirror2d(self.mirrored)
         pattern.rotate_around((0.0, 0.0), self.rotation)
         pattern.translate_elements(self.offset)
         pattern.scale_element_doses(self.dose)
diff --git a/masque/traits/annotatable.py b/masque/traits/annotatable.py
index 9d49018..4c0fdaa 100644
--- a/masque/traits/annotatable.py
+++ b/masque/traits/annotatable.py
@@ -3,7 +3,7 @@ from typing import TypeVar
 from abc import ABCMeta, abstractmethod
 
 from ..utils import annotations_t
-from ..error import PatternError
+from ..error import MasqueError
 
 
 T = TypeVar('T', bound='Annotatable')
@@ -51,5 +51,5 @@ class AnnotatableImpl(Annotatable, metaclass=ABCMeta):
     @annotations.setter
     def annotations(self, annotations: annotations_t):
         if not isinstance(annotations, dict):
-            raise PatternError(f'annotations expected dict, got {type(annotations)}')
+            raise MasqueError(f'annotations expected dict, got {type(annotations)}')
         self._annotations = annotations
diff --git a/masque/traits/doseable.py b/masque/traits/doseable.py
index 217872c..8fd770a 100644
--- a/masque/traits/doseable.py
+++ b/masque/traits/doseable.py
@@ -1,7 +1,7 @@
 from typing import TypeVar
 from abc import ABCMeta, abstractmethod
 
-from ..error import PatternError
+from ..error import MasqueError
 
 
 T = TypeVar('T', bound='Doseable')
@@ -65,7 +65,7 @@ class DoseableImpl(Doseable, metaclass=ABCMeta):
     @dose.setter
     def dose(self, val: float):
         if not val >= 0:
-            raise PatternError('Dose must be non-negative')
+            raise MasqueError('Dose must be non-negative')
         self._dose = val
 
     '''
diff --git a/masque/traits/mirrorable.py b/masque/traits/mirrorable.py
index 1ec54f6..6990e4c 100644
--- a/masque/traits/mirrorable.py
+++ b/masque/traits/mirrorable.py
@@ -1,4 +1,4 @@
-from typing import TypeVar
+from typing import TypeVar, Tuple
 from abc import ABCMeta, abstractmethod
 
 
@@ -28,6 +28,22 @@ class Mirrorable(metaclass=ABCMeta):
         """
         pass
 
+    def mirror2d(self: T, axes: Tuple[bool, bool]) -> T:
+        """
+        Optionally mirror the entity across both axes
+
+        Args:
+            axes: (mirror_across_x, mirror_across_y)
+
+        Returns:
+            self
+        """
+        if axes[0]:
+            self.mirror(0)
+        if axes[1]:
+            self.mirror(1)
+        return self
+
 
 #class MirrorableImpl(Mirrorable, metaclass=ABCMeta):
 #    """
@@ -50,7 +66,7 @@ class Mirrorable(metaclass=ABCMeta):
 #    @mirrored.setter
 #    def mirrored(self, val: Sequence[bool]):
 #        if is_scalar(val):
-#            raise PatternError('Mirrored must be a 2-element list of booleans')
+#            raise MasqueError('Mirrored must be a 2-element list of booleans')
 #        self._mirrored = numpy.array(val, dtype=bool, copy=True)
 #
 #    '''
diff --git a/masque/traits/positionable.py b/masque/traits/positionable.py
index 71f90ec..4e59e32 100644
--- a/masque/traits/positionable.py
+++ b/masque/traits/positionable.py
@@ -4,7 +4,7 @@ from typing import TypeVar
 from abc import ABCMeta, abstractmethod
 import numpy        # type: ignore
 
-from ..error import PatternError
+from ..error import MasqueError
 from ..utils import vector2
 
 
@@ -97,7 +97,7 @@ class PositionableImpl(Positionable, metaclass=ABCMeta):
             val = numpy.array(val, dtype=float)
 
         if val.size != 2:
-            raise PatternError('Offset must be convertible to size-2 ndarray')
+            raise MasqueError('Offset must be convertible to size-2 ndarray')
         self._offset = val.flatten()
 
     '''
diff --git a/masque/traits/repeatable.py b/masque/traits/repeatable.py
index 4a7f391..9f032b7 100644
--- a/masque/traits/repeatable.py
+++ b/masque/traits/repeatable.py
@@ -1,7 +1,7 @@
 from typing import TypeVar, Optional, TYPE_CHECKING
 from abc import ABCMeta, abstractmethod
 
-from ..error import PatternError
+from ..error import MasqueError
 
 
 if TYPE_CHECKING:
@@ -71,7 +71,7 @@ class RepeatableImpl(Repeatable, metaclass=ABCMeta):
     def repetition(self, repetition: Optional['Repetition']):
         from ..repetition import Repetition
         if repetition is not None and not isinstance(repetition, Repetition):
-            raise PatternError(f'{repetition} is not a valid Repetition object!')
+            raise MasqueError(f'{repetition} is not a valid Repetition object!')
         self._repetition = repetition
 
     '''
diff --git a/masque/traits/rotatable.py b/masque/traits/rotatable.py
index c0641f0..1e83697 100644
--- a/masque/traits/rotatable.py
+++ b/masque/traits/rotatable.py
@@ -5,7 +5,7 @@ import numpy        # type: ignore
 from numpy import pi
 
 #from .positionable import Positionable
-from ..error import PatternError
+from ..error import MasqueError
 from ..utils import is_scalar, rotation_matrix_2d, vector2
 
 T = TypeVar('T', bound='Rotatable')
@@ -24,12 +24,12 @@ class Rotatable(metaclass=ABCMeta):
     ---- Abstract methods
     '''
     @abstractmethod
-    def rotate(self: T, theta: float) -> T:
+    def rotate(self: T, val: float) -> T:
         """
         Rotate the shape around its origin (0, 0), ignoring its offset.
 
         Args:
-            theta: Angle to rotate by (counterclockwise, radians)
+            val: Angle to rotate by (counterclockwise, radians)
 
         Returns:
             self
@@ -56,8 +56,8 @@ class RotatableImpl(Rotatable, metaclass=ABCMeta):
 
     @rotation.setter
     def rotation(self, val: float):
-        if not is_scalar(val):
-            raise PatternError('Rotation must be a scalar')
+        if not numpy.size(val) == 1:
+            raise MasqueError('Rotation must be a scalar')
         self._rotation = val % (2 * pi)
 
     '''
diff --git a/masque/traits/scalable.py b/masque/traits/scalable.py
index b31c2f9..ec87c69 100644
--- a/masque/traits/scalable.py
+++ b/masque/traits/scalable.py
@@ -1,7 +1,7 @@
 from typing import TypeVar
 from abc import ABCMeta, abstractmethod
 
-from ..error import PatternError
+from ..error import MasqueError
 from ..utils import is_scalar
 
 
@@ -51,9 +51,9 @@ class ScalableImpl(Scalable, metaclass=ABCMeta):
     @scale.setter
     def scale(self, val: float):
         if not is_scalar(val):
-            raise PatternError('Scale must be a scalar')
+            raise MasqueError('Scale must be a scalar')
         if not val > 0:
-            raise PatternError('Scale must be positive')
+            raise MasqueError('Scale must be positive')
         self._scale = val
 
     '''
diff --git a/masque/utils.py b/masque/utils.py
index a09a09c..9588ee6 100644
--- a/masque/utils.py
+++ b/masque/utils.py
@@ -120,12 +120,12 @@ def remove_colinear_vertices(vertices: numpy.ndarray, closed_path: bool = True)
     Returns:
         `vertices` with colinear (superflous) vertices removed.
     """
-    vertices = numpy.array(vertices)
+    vertices = remove_duplicate_vertices(vertices)
 
     # Check for dx0/dy0 == dx1/dy1
 
     dv = numpy.roll(vertices, -1, axis=0) - vertices  # [y1-y0, y2-y1, ...]
-    dxdy = dv * numpy.roll(dv, 1, axis=0)[:, ::-1]    # [[dx0*(dy_-1), (dx_-1)*dy0], dx1*dy0, dy1*dy0]]
+    dxdy = dv * numpy.roll(dv, 1, axis=0)[:, ::-1]    # [[dx0*(dy_-1), (dx_-1)*dy0], dx1*dy0, dy1*dx0]]
 
     dxdy_diff = numpy.abs(numpy.diff(dxdy, axis=1))[:, 0]
     err_mult = 2 * numpy.abs(dxdy).sum(axis=1) + 1e-40
diff --git a/setup.py b/setup.py
index ff8aad9..c9c91ed 100644
--- a/setup.py
+++ b/setup.py
@@ -3,11 +3,11 @@
 from setuptools import setup, find_packages
 
 
-with open('README.md', 'r') as f:
+with open('README.md', 'rt') as f:
     long_description = f.read()
 
-with open('masque/VERSION', 'r') as f:
-    version = f.read().strip()
+with open('masque/VERSION.py', 'rt') as f:
+    version = f.readlines()[2].strip()
 
 setup(name='masque',
       version=version,
@@ -19,16 +19,15 @@ setup(name='masque',
       url='https://mpxd.net/code/jan/masque',
       packages=find_packages(),
       package_data={
-          'masque': ['VERSION',
-                     'py.typed',
+          'masque': ['py.typed',
                      ]
       },
       install_requires=[
-            'numpy',
+          'numpy',
       ],
       extras_require={
           'gdsii': ['python-gdsii'],
-          'klamath': ['klamath'],
+          'klamath': ['klamath>=0.3'],
           'oasis': ['fatamorgana>=0.7'],
           'dxf': ['ezdxf'],
           'svg': ['svgwrite'],