使用 matplotlib 选择和编辑特定标记

Question

我正在尝试使 Line2d 对象上的单个标记可拖动。我已经看到这是如何在Matplotlib's draggable rectangle example. 中使用 bar() 完成的。这里的根本区别是ax.bar(...) 生成一组艺术家，而ax.plot(...) 返回单个 Line2D 对象，而我发现了如何编辑属性在整行中，我不知道如何编辑该行中单个标记元素的属性，而且我搜索了文档并且找不到任何东西。我是否需要通过使用 Circle() 对象作为我的“标记”，然后将线连续重绘为 motion_notify_event 来做到这一点？我可以在这里粘贴我的代码，但保证它根本上是错误的（哈哈）。

Answer 1

您有几种方法可以做到这一点。我怀疑您是否有一种简单的方法来拖动线本身。要拖动线标记（但看不到任何标记），只需确保它们存在但透明即可。我将使用 matplotlib 文档中的一个示例：The Path Editor。

这里是修改后的代码：

import numpy as np
import matplotlib.path as mpath
import matplotlib.patches as mpatches
import matplotlib.pyplot as plt

Path = mpath.Path

fig, ax = plt.subplots()

pathdata = [
    (Path.MOVETO, (1.58, -2.57)),
    (Path.MOVETO, (0.35, -1.1)),
    (Path.MOVETO, (-1.75, 2.0)),
    (Path.MOVETO, (0.375, 2.0)),
    (Path.MOVETO, (0.85, 1.15)),
    (Path.MOVETO, (2.2, 3.2)),
    (Path.MOVETO, (3, 0.05)),
    (Path.MOVETO, (2.0, -0.5)),
    #(Path.CLOSEPOLY, (1.58, -2.57)),
    ]

codes, verts = zip(*pathdata)
path = mpath.Path(verts, codes)
patch = mpatches.PathPatch(path, facecolor='green', edgecolor='yellow', alpha=0.5)
ax.add_patch(patch)


class PathInteractor(object):
    """
    An path editor.

    Key-bindings

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


    """

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

    def __init__(self, pathpatch):

        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.line.set_markerfacecolor((1, 1, 0, 0))

        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

    def draw_callback(self, event):
        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 pathpatch_changed(self, pathpatch):
        'this method is called whenever the pathpatchgon object is called'
        # only copy the artist props to the line (except visibility)
        vis = self.line.get_visible()
        plt.Artist.update_from(self.line, pathpatch)
        self.line.set_visible(vis)  # don't use the pathpatch 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.pathpatch.get_path().vertices)
        xyt = self.pathpatch.get_transform().transform(xy)
        xt, yt = xyt[:, 0], xyt[:, 1]
        d = np.sqrt((xt - event.x)**2 + (yt - event.y)**2)
        ind = d.argmin()

        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

        self.canvas.draw()

    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

        vertices = self.pathpatch.get_path().vertices

        vertices[self._ind] = x, y
        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)


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

plt.show()

你需要特别考虑的一行是：

self.line.set_markerfacecolor((1, 1, 0, 0))

它位于 plot 定义之后的 __init__ 函数中。最后一个数字是 alpha 通道，我将其设为零。情节本身如下所示：

你可以拖动线标记，尽管你需要猜测它们在哪里（但我假设你有一架飞机）。

在任何情况下，如果您选择使用此示例，请确保将行数据转换为路径。

编辑：让我举一个例子来说明如何进行这条路径构建（不妨将其作为一个完整的例子）：

import numpy as np

def buildpath(x,y):
    path = []
    for i in range(len(x)):
        path.append((Path.MOVETO, (x[i], y[i])))
    return path

x = np.linspace(-2,2,5)
y = x*1
pathdata = buildpath(x,y)

如果您使用它来构建您的pathdata（其余代码保持不变），您应该使用 numpy 数组获取个性化路径（就像您通常在 matplotlib 中使用绘图命令一样）。