如何在 matplotlib 中控制鼠标可拖动点的点移动方向

使用以下作为参考：交互式 BSpline Fitting我有以下工具可以使用鼠标在任何方向拖动样条的点：

import numpy as np
from  scipy.interpolate import interp1d
from matplotlib.lines import Line2D
from matplotlib.artist import Artist
from matplotlib.mlab import dist_point_to_segment


class PolygonInteractor(object):

"""
A polygon editor.
https://matplotlib.org/gallery/event_handling/poly_editor.html

Key-bindings

  't' toggle vertex markers on and off.  When vertex markers are on,
      you can move them, delete them

  'd' delete the vertex under point

  'i' insert a vertex at point.  You must be within epsilon of the
      line connecting two existing vertices

"""

showverts = True
epsilon = 5  # max pixel distance to count as a vertex hit

def __init__(self, ax, poly, visible=False):
    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
    self.poly.set_visible(visible)

    x, y = zip(*self.poly.xy)
    self.line = Line2D(x, y, ls="",
                       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.draw_callback)
    canvas.mpl_connect('button_press_event', self.button_press_callback)
    canvas.mpl_connect('key_press_event', self.key_press_callback)
    canvas.mpl_connect('button_release_event', self.button_release_callback)
    canvas.mpl_connect('motion_notify_event', self.motion_notify_callback)
    self.canvas = canvas

    x,y = self.interpolate()
    self.line2 = Line2D(x, y, animated=True)
    self.ax.add_line(self.line2)

def interpolate(self):
    x, y = self.poly.xy[:].T
    i = np.arange(len(x))

    interp_i = np.linspace(0, i.max(), 100 * i.max())

    xi = interp1d(i, x, kind='cubic')(interp_i)  
    yi = interp1d(i, y, kind='cubic')(interp_i)

    return xi,yi

def draw_callback(self, event):
    self.background = self.canvas.copy_from_bbox(self.ax.bbox)
    self.ax.draw_artist(self.poly)
    self.ax.draw_artist(self.line)
    self.ax.draw_artist(self.line2)
    # do not need to blit here, this will fire before the screen is
    # updated

def poly_changed(self, poly):
    'this method is called whenever the polygon object is called'
    # only copy the artist props to the line (except visibility)
    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):
    'get the index of the vertex under point if within epsilon tolerance'

    # display coords
    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 button_press_callback(self, event):
    'whenever a mouse button is pressed'
    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 button_release_callback(self, event):
    'whenever a mouse button is released'
    if not self.showverts:
        return
    if event.button != 1:
        return
    self._ind = None

def key_press_callback(self, event):
    'whenever a key is pressed'
    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 motion_notify_callback(self, event):
    'on mouse movement'
    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))

    x,y = self.interpolate()
    self.line2.set_data(x,y)

    self.canvas.restore_region(self.background)
    self.ax.draw_artist(self.poly)
    self.ax.draw_artist(self.line)
    self.ax.draw_artist(self.line2)
    self.canvas.blit(self.ax.bbox)


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

#theta = np.arange(0, 2*np.pi, 0.1)
#r = 1.5

#xs = r*np.cos(theta)
#ys = r*np.sin(theta)
xs = (921, 951, 993, 1035, 1065, 1045, 993, 945)
ys = (1181, 1230, 1243, 1230, 1181, 1130, 1130, 1130)

poly = Polygon(list(zip(xs, ys)), animated=True)

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

ax.set_title('Click and drag a point to move it')

ax.set_xlim((800, 1300))
ax.set_ylim((1000, 1300))

plt.show()

如果样条如下：

我想添加额外的约束：

1）C点和G点的移动应仅限于Y轴或垂直方向，即用户只能向上或向下拖动点，不能向左或向右拖动

2）A点和E点的移动应该仅限于X轴或水平方向，即用户只能左右拖动点，不能上下拖动

有人可以建议如何将这些约束添加到给定的点吗？

编辑 -

当我将点 A 向左/向右拖动一定数量的“d0”时，然后点 E 需要分别由“d0”向右/向左拖动。我试图仅通过在拖动点时反复将更改后的 y 坐标设置回其原始值来限制这两个点沿水平方向的移动。但是它并没有反映在代码中。

相对于具有坐标 (993,1181) 的参考中心点计算移动量“d0”

我尝试通过编辑 motion_notify_callback() 函数按如下方式执行此操作：

    def motion_notify_callback(self, event):
    'on mouse movement'
    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))

    xpts,ypts,x,y = self.interpolate()
    #Note that in xpts and ypts, we are getting the new coordinates of
    #the points after dragging

    if(xpts[0]<xs[0]): 
        #when point A is being dragged outwards(towards left)
            d0=abs(993-xpts[0])
            #movement amount

            ypts[0]=ys[0] #setting the y value of dragged point back to
            #original value to constrain the movement along horizontal
            #direction only. This is however not being reflected
            xpts[4] = 993+d0 #moving point E by same amount to the right
            ypts[4]=ys[4] #Trying to stop E from moving in Y direction
            d0=0

    elif(xpts[0]>xs[0]):
             #when point A is moved inwards/towards right

            d0=abs(993-xpts[0])
            ypts[0]=ys[0]
            xnew=993+d0
            xpts[4] = xnew #moving E inwards/towards left by same amount
            ypts[4]=ys[4]
            d0=0

     self.line2.set_data(x,y)
     self.canvas.restore_region(self.background)
     self.ax.draw_artist(self.poly)
     self.ax.draw_artist(self.line)
     self.ax.draw_artist(self.line2)
     self.canvas.blit(self.ax.bbox)
     return d0