plot.png

pyclipper_demo

#!/usr/bin/env python3
# demo of polygon shrinking / growing (called inward/outward polygon offseting)
# using pyclipper
# 04/2022 created

from typing import List, Tuple
import pyclipper
import matplotlib.pyplot as plt


def plotPolygon(points, color='r', lineWidth=1):
    x, y = map(list, zip(*points))
    x.append(x[0])
    y.append(y[0])
    plt.plot(x, y, marker='o', color=color, linewidth=lineWidth)


def plotPolygons(polgons, color, lineWidth):
    for pl in polgons:
        plotPolygon(pl, color, lineWidth=lineWidth)


# ---------- MAIN ------------

point_list = (
    (348, 257), (364, 148), (322, 148), (326, 241),
    (295, 219), (258, 88), (440, 129), (370, 196),
    (472, 275)
)

pco = pyclipper.PyclipperOffset()
pco.AddPath(point_list, pyclipper.JT_ROUND, pyclipper.ET_CLOSEDPOLYGON)
contours_list_shrink: List[List[Tuple[int, int]]] = pco.Execute(-20.0)  # "-" --> shrink the outline
contours_list_grow: List[List[Tuple[int, int]]] = pco.Execute(20.0)  # grow the outline

# ---- plot
plotPolygon(point_list, 'b', 1)
plotPolygons(contours_list_shrink, 'r', 3)
plotPolygons(contours_list_grow, 'orange', 3)
plt.axis("off")
plt.show()