Matplotlib – Path Editor
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A Path Editor is an application that allows users to interactively edit and manipulate paths in a graphical environment. In the context of Matplotlib, a Path Editor typically refers to a graphical user interface (GUI) application that facilitates the editing of paths defined using Matplotlib”s Path class.
Before diving into the Path Editor, it”s essential to understand the basics of Matplotlib paths. A Path is a fundamental object in Matplotlib that contains various elements like line segments, curves, and shapes within the matplotlib.patches module. Paths provide a versatile way to define complex outlines by specifying a series of commands such as moveto, lineto, and curveto.
Matplotlib offers a powerful Path class that serves as the foundation for creating and manipulating paths in visualizations.
Step by Step implementation
In this tutorial, we”ll explore the Matplotlib Path Editor, a cross-GUI application that uses Matplotlib”s event handling capabilities to edit and modify paths on the canvas interactively.
Creating the PathInteractor class
Create a path editor (PathInteractor) class to handle the interaction with the defined path. This class includes methods to toggle vertex markers (using the ”t” key), drag vertices, and respond to mouse and key events.
Example
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.backend_bases import MouseButton
from matplotlib.patches import PathPatch
from matplotlib.path import Path
class PathInteractor:
showverts = True
# max pixel distance to count as a vertex hit
epsilon = 5
def __init__(self, pathpatch):
# Initialization and event connections
self.ax = pathpatch.axes
canvas = self.ax.figure.canvas
self.pathpatch = pathpatch
self.pathpatch.set_animated(True)
x, y = zip(*self.pathpatch.get_path().vertices)
self.line, = ax.plot(
x, y, marker=”o”, markerfacecolor=”r”, animated=True)
self._ind = None # the active vertex
canvas.mpl_connect(”draw_event”, self.on_draw)
canvas.mpl_connect(”button_press_event”, self.on_button_press)
canvas.mpl_connect(”key_press_event”, self.on_key_press)
canvas.mpl_connect(”button_release_event”, self.on_button_release)
canvas.mpl_connect(”motion_notify_event”, self.on_mouse_move)
self.canvas = canvas
def get_ind_under_point(self, event):
# Return the index of the point closest to the event position or *None*
xy = self.pathpatch.get_path().vertices
xyt = self.pathpatch.get_transform().transform(xy) # to display coords
xt, yt = xyt[:, 0], xyt[:, 1]
d = np.sqrt((xt – event.x)**2 + (yt – event.y)**2)
ind = d.argmin()
return ind if d[ind] < self.epsilon else None
def on_draw(self, event):
# Callback for draws.
self.background = self.canvas.copy_from_bbox(self.ax.bbox)
self.ax.draw_artist(self.pathpatch)
self.ax.draw_artist(self.line)
self.canvas.blit(self.ax.bbox)
def on_button_press(self, event):
# Callback for mouse button presses
if (event.inaxes is None
or event.button != MouseButton.LEFT
or not self.showverts):
return
self._ind = self.get_ind_under_point(event)
def on_button_release(self, event):
# Callback for mouse button releases
if (event.button != MouseButton.LEFT
or not self.showverts):
return
self._ind = None
def on_key_press(self, event):
# Callback for key presses
if not event.inaxes:
return
if event.key == ”t”:
self.showverts = not self.showverts
self.line.set_visible(self.showverts)
if not self.showverts:
self._ind = None
self.canvas.draw()
def on_mouse_move(self, event):
# Callback for mouse movements
if (self._ind is None
or event.inaxes is None
or event.button != MouseButton.LEFT
or not self.showverts):
return
vertices = self.pathpatch.get_path().vertices
vertices[self._ind] = event.xdata, event.ydata
self.line.set_data(zip(*vertices))
self.canvas.restore_region(self.background)
self.ax.draw_artist(self.pathpatch)
self.ax.draw_artist(self.line)
self.canvas.blit(self.ax.bbox)
Event Handling and Canvas Interaction
The PathInteractor class connects various callbacks to canvas events, enabling users to interact with the defined path. These interactions include pressing and releasing mouse buttons, dragging vertices, and toggling vertex markers with key presses.
canvas.mpl_connect(”draw_event”, self.on_draw)
canvas.mpl_connect(”button_press_event”, self.on_button_press)
canvas.mpl_connect(”key_press_event”, self.on_key_press)
canvas.mpl_connect(”button_release_event”, self.on_button_release)
canvas.mpl_connect(”motion_notify_event”, self.on_mouse_move)
Defining and Visualizing a Path
Start by defining a predefined path, consisting of various path codes and vertices, which is created using the Matplotlib Path class. This path is then visualized on the canvas using a PathPatch instance, adding an interactive component to the plot.
fig, ax = plt.subplots()
pathdata = [
(Path.MOVETO, (1.58, -2.57)),
(Path.CURVE4, (0.35, -1.1)),
(Path.CURVE4, (-1.75, 2.0)),
(Path.CURVE4, (0.375, 2.0)),
(Path.LINETO, (0.85, 1.15)),
(Path.CURVE4, (2.2, 3.2)),
(Path.CURVE4, (3, 0.05)),
(Path.CURVE4, (2.0, -0.5)),
(Path.CLOSEPOLY, (1.58, -2.57)),
]
codes, verts = zip(*pathdata)
path = Path(verts, codes)
patch = PathPatch(
path, facecolor=”green”, edgecolor=”yellow”, alpha=0.5)
ax.add_patch(patch)
Running the Path Editor
Instantiate the PathInteractor class, set plot properties, and display the plot. Users can now interactively drag vertices, toggle vertex markers using the key “t”, and observe real-time updates.
interactor = PathInteractor(patch)
ax.set_title(”drag vertices to update path”)
ax.set_xlim(-3, 4)
ax.set_ylim(-3, 4)
plt.show()
Example
Let’s see the complete example of the Matplotlib Path Editor.
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.backend_bases import MouseButton
from matplotlib.patches import PathPatch
from matplotlib.path import Path
class PathInteractor:
showverts = True
# max pixel distance to count as a vertex hit
epsilon = 5
def __init__(self, pathpatch):
# Initialization and event connections
self.ax = pathpatch.axes
canvas = self.ax.figure.canvas
self.pathpatch = pathpatch
self.pathpatch.set_animated(True)
x, y = zip(*self.pathpatch.get_path().vertices)
self.line, = ax.plot(
x, y, marker=”o”, markerfacecolor=”r”, animated=True)
self._ind = None # the active vertex
canvas.mpl_connect(”draw_event”, self.on_draw)
canvas.mpl_connect(”button_press_event”, self.on_button_press)
canvas.mpl_connect(”key_press_event”, self.on_key_press)
canvas.mpl_connect(”button_release_event”, self.on_button_release)
canvas.mpl_connect(”motion_notify_event”, self.on_mouse_move)
self.canvas = canvas
def get_ind_under_point(self, event):
# Return the index of the point closest to the event position or *None*
xy = self.pathpatch.get_path().vertices
xyt = self.pathpatch.get_transform().transform(xy) # to display coords
xt, yt = xyt[:, 0], xyt[:, 1]
d = np.sqrt((xt – event.x)**2 + (yt – event.y)**2)
ind = d.argmin()
return ind if d[ind] < self.epsilon else None
def on_draw(self, event):
# Callback for draws.
self.background = self.canvas.copy_from_bbox(self.ax.bbox)
self.ax.draw_artist(self.pathpatch)
self.ax.draw_artist(self.line)
self.canvas.blit(self.ax.bbox)
def on_button_press(self, event):
# Callback for mouse button presses
if (event.inaxes is None
or event.button != MouseButton.LEFT
or not self.showverts):
return
self._ind = self.get_ind_under_point(event)
def on_button_release(self, event):
# Callback for mouse button releases
if (event.button != MouseButton.LEFT
or not self.showverts):
return
self._ind = None
def on_key_press(self, event):
# Callback for key presses
if not event.inaxes:
return
if event.key == ”t”:
self.showverts = not self.showverts
self.line.set_visible(self.showverts)
if not self.showverts:
self._ind = None
self.canvas.draw()
def on_mouse_move(self, event):
# Callback for mouse movements
if (self._ind is None
or event.inaxes is None
or event.button != MouseButton.LEFT
or not self.showverts):
return
vertices = self.pathpatch.get_path().vertices
vertices[self._ind] =