Matplotlib - 多邊形編輯器

多邊形編輯器 (Poly Editor) 是多邊形編輯器 (Polygon Editor) 的簡稱，它是一個允許使用者在圖形環境中互動式編輯和操作多邊形頂點的應用程式。

在 Matplotlib 的上下文中，多邊形編輯器通常指的是一個跨GUI應用程式，它允許使用者互動式修改畫布上顯示的多邊形。此應用程式提供了諸如新增、刪除和移動多邊形頂點，以及使用滑鼠點選和鍵繫結調整其形狀和位置等功能。

本教程將演示如何使用 Matplotlib 的事件處理功能建立多邊形編輯器。

建立多邊形互動類

要建立多邊形編輯器，請定義一個名為 PolygonInteractor 的 Python 類，該類處理與多邊形頂點的互動。此類實現事件處理方法以響應使用者互動：

• on_draw - 處理多邊形及其頂點的繪製。

• on_button_press - 響應滑鼠按鈕按下以選擇頂點。

• on_button_release - 處理滑鼠按鈕釋放。

• on_key_press - 處理按鍵以切換頂點標記（使用“t”鍵）、刪除頂點（使用“d”鍵）或插入新頂點（使用“i”鍵）。

• on_mouse_move - 處理滑鼠移動以拖動頂點並更新多邊形。

以下是 PolygonInteractor 類的實現：

class PolygonInteractor:

   showverts = True
   epsilon = 3

   def __init__(self, ax, poly):
      if poly.figure is None:
         raise RuntimeError('You must first add the polygon to a figure '
            'or canvas before defining the interactor')
      self.ax = ax
      canvas = poly.figure.canvas
      self.poly = poly

      x, y = zip(*self.poly.xy)
      self.line = Line2D(x, y,
         marker='o', markerfacecolor='r',
         animated=True)
      self.ax.add_line(self.line)

      self.cid = self.poly.add_callback(self.poly_changed)
      self._ind = None  # the active vert

      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 on_draw(self, event):
      self.background = self.canvas.copy_from_bbox(self.ax.bbox)
      self.ax.draw_artist(self.poly)
      self.ax.draw_artist(self.line)
       

   def poly_changed(self, poly):
      vis = self.line.get_visible()
      Artist.update_from(self.line, poly)
      self.line.set_visible(vis)  # don't use the poly visibility state

   def get_ind_under_point(self, event):
      xy = np.asarray(self.poly.xy)
      xyt = self.poly.get_transform().transform(xy)
      xt, yt = xyt[:, 0], xyt[:, 1]
      d = np.hypot(xt - event.x, yt - event.y)
      indseq, = np.nonzero(d == d.min())
      ind = indseq[0]

      if d[ind] >= self.epsilon:
         ind = None

         return ind

   def on_button_press(self, event):
       
      if not self.showverts:
         return
      if event.inaxes is None:
         return
      if event.button != 1:
         return
      self._ind = self.get_ind_under_point(event)

   def on_button_release(self, event):
       
      if not self.showverts:
         return
      if event.button != 1:
         return
      self._ind = None

   def on_key_press(self, event):
       
      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
      elif event.key == 'd':
         ind = self.get_ind_under_point(event)
         if ind is not None:
            self.poly.xy = np.delete(self.poly.xy,
               ind, axis=0)
            self.line.set_data(zip(*self.poly.xy))
      elif event.key == 'i':
         xys = self.poly.get_transform().transform(self.poly.xy)
         p = event.x, event.y  # display coords
         for i in range(len(xys) - 1):
            s0 = xys[i]
            s1 = xys[i + 1]
            d = dist_point_to_segment(p, s0, s1)
            if d <= self.epsilon:
               self.poly.xy = np.insert(
                  self.poly.xy, i+1,
                  [event.xdata, event.ydata],
                  axis=0)
               self.line.set_data(zip(*self.poly.xy))
               break
      if self.line.stale:
         self.canvas.draw_idle()

   def on_mouse_move(self, event):
      if not self.showverts:
         return
      if self._ind is None:
         return
      if event.inaxes is None:
         return
      if event.button != 1:
         return
      x, y = event.xdata, event.ydata

      self.poly.xy[self._ind] = x, y
      if self._ind == 0:
         self.poly.xy[-1] = x, y
      elif self._ind == len(self.poly.xy) - 1:
         self.poly.xy[0] = x, y
      self.line.set_data(zip(*self.poly.xy))

      self.canvas.restore_region(self.background)
      self.ax.draw_artist(self.poly)
      self.ax.draw_artist(self.line)
      self.canvas.blit(self.ax.bbox)

定義實用程式函式

定義一個實用程式函式 dist_point_to_segment 來計算點和線段之間的距離。此函式用於確定在互動過程中哪個頂點最接近滑鼠游標。

def dist_point_to_segment(p, s0, s1):
   s01 = s1 - s0
   s0p = p - s0
   if (s01 == 0).all():
      return np.hypot(*s0p)

   p1 = s0 + np.clip((s0p @ s01) / (s01 @ s01), 0, 1) * s01
   return np.hypot(*(p - p1))

初始化多邊形編輯器

要初始化多邊形編輯器，我們需要建立一個 PolygonInteractor 類的例項，並將軸物件和多邊形物件傳遞給它。

if __name__ == '__main__':
   import matplotlib.pyplot as plt

   from matplotlib.patches import Polygon

   theta = np.arange(0, 2*np.pi, 0.2)
   r = 1.5

   xs = r * np.cos(theta)
   ys = r * np.sin(theta)

   poly = Polygon(np.column_stack([xs, ys]), animated=True)

   fig, ax = plt.subplots()
   ax.add_patch(poly)
   p = PolygonInteractor(ax, poly)

   ax.set_title('Click and drag a point to move it')
   ax.set_xlim((-2, 2))
   ax.set_ylim((-2, 2))
   plt.show()

執行多邊形編輯器

透過執行下面提供的完整程式碼，我們將得到一個 Matplotlib 視窗，其中顯示帶有多邊形的繪圖。我們可以透過單擊和拖動其頂點與多邊形進行互動，透過按“t”鍵切換頂點標記，按“d”鍵刪除頂點，按“i”鍵插入新頂點。

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()

輸出

執行上述程式碼後，我們將獲得以下輸出：

觀看下面的影片以觀察此應用程式的工作方式：