Creating a Compound Path

Introduction

In this tutorial, we will learn how to create a compound path using Matplotlib in Python. A compound path is a collection of simple paths that can be used to create complex shapes. We will create a compound path by combining two simple polygons, a rectangle, and a triangle.

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Importing the Required Libraries

We will start by importing the required libraries. We need matplotlib.pyplot for creating the plot, matplotlib.patches for creating patches, matplotlib.path.Path for creating paths, and numpy for creating arrays.

import matplotlib.pyplot as plt
from matplotlib.patches import PathPatch
from matplotlib.path import Path
import numpy as np

Creating the Vertices and Codes

We will create the vertices and codes for the two polygons that we want to combine into a compound path. We will use Path.MOVETO to move the cursor to the starting point of the polygon, Path.LINETO to create a line from the starting point to the next point, and Path.CLOSEPOLY to close the polygon.

vertices = []
codes = []

## First Polygon - Rectangle
codes = [Path.MOVETO] + [Path.LINETO]*3 + [Path.CLOSEPOLY]
vertices = [(1, 1), (1, 2), (2, 2), (2, 1), (0, 0)]

## Second Polygon - Triangle
codes += [Path.MOVETO] + [Path.LINETO]*2 + [Path.CLOSEPOLY]
vertices += [(4, 4), (5, 5), (5, 4), (0, 0)]

Creating the Path

We will use Path to create the path from the vertices and codes that we created in the previous step.

path = Path(vertices, codes)

Creating the PathPatch

We will create a PathPatch from the path that we created in the previous step. We will set the facecolor to 'none' and the edgecolor to 'green'.

pathpatch = PathPatch(path, facecolor='none', edgecolor='green')

Creating the Plot

We will create the plot and add the PathPatch to the plot. We will set the title of the plot to 'A Compound Path'.

fig, ax = plt.subplots()
ax.add_patch(pathpatch)
ax.set_title('A Compound Path')

ax.autoscale_view()

plt.show()

Summary

In this tutorial, we learned how to create a compound path using Matplotlib in Python. We created a compound path by combining two simple polygons, a rectangle, and a triangle. We used Path to create the path from the vertices and codes, and PathPatch to create a patch from the path. Finally, we added the patch to the plot to display the compound path.