Matplotlib 简明教程

Matplotlib - Path Editor

Path Editor 是一款应用程序，允许用户在图形化环境中交互式编辑和操作路径。在 Matplotlib 中，路径编辑器通常指图形化用户界面 (GUI) 应用程序，它简化了使用 Matplotlib 的路径类定义路径的编辑工作。

在深入探究路径编辑器之前，理解 Matplotlib 路径的基础知识至关重要。 Path 是 Matplotlib 中的基本对象，它包含 matplotlib.patches 模块中的各种元素，如线段、曲线和形状。路径提供了一种用综合的轮廓定义复杂轮廓的方法，方法是指定一系列命令，例如 moveto、lineto 和 curveto。

Matplotlib 提供一个功能强大的 Path class ，它是可视化中创建和操纵路径的基础。

Step by Step implementation

在本教程中，我们将探讨 Matplotlib 路径编辑器，这是一个 cross-GUI application ，它使用 Matplotlib 的事件处理功能以交互式方式编辑和修改画布中的路径。

Creating the PathInteractor class

创建一个路径编辑器 (PathInteractor) 类来处理与已定义路径的交互。这个类包括用于切换顶点标记（使用 “t” 键）、拖动顶点以及响应鼠标和键盘事件的方法。

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

PathInteractor 类将各种回调连接到画布事件，使用户能够与已定义的路径交互。这些交互包括按下并释放鼠标按钮、拖动顶点以及按键盘键来切换顶点标记。

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

首先定义一个预定义路径，该路径由各种路径代码和顶点组成，使用 Matplotlib 路径类创建。然后使用 PathPatch 实例在画布上将该路径可视化，添加交互式组件到绘图中。

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

实例化 PathInteractor 类、设置绘图属性并显示绘图。用户现在可以交互拖动顶点、使用键 "t" 切换顶点标记并且观察实时更新。

interactor = PathInteractor(patch)
ax.set_title('drag vertices to update path')
ax.set_xlim(-3, 4)
ax.set_ylim(-3, 4)

plt.show()

我们来看 Matplotlib 路径编辑器的完整示例。

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)

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)

interactor = PathInteractor(patch)
ax.set_title('drag vertices to update path')
ax.set_xlim(-3, 4)
ax.set_ylim(-3, 4)

plt.show()

在执行以上程序后，您将得到以下图表。在键盘上按 “t” 键。此操作将打开或关闭顶点标记的可见性。当顶点标记可见（在按 “t” 后）时，您可以使用鼠标拖动这些标记。观察拖动顶点如何影响路径的形状。

path editor

观看下面的视频以观察路径编辑器如何在此处工作。

path editor