matplotlib绘制鼠标的十字光标的实现(自定义方式，官方实例)
matplotlib在widgets模块提供Cursor类用于支持十字光标的生成。另外官方还提供了自定义十字光标的实例。
widgets模块Cursor类源码
class Cursor(AxesWidget):
"""
A crosshair cursor that spans the axes and moves with mouse cursor.
For the cursor to remain responsive you must keep a reference to it.
Parameters
----------
ax : `matplotlib.axes.Axes`
The `~.axes.Axes` to attach the cursor to.
horizOn : bool, default: True
Whether to draw the horizontal line.
vertOn : bool, default: True
Whether to draw the vertical line.
useblit : bool, default: False
Use blitting for faster drawing if supported by the backend.
Other Parameters
----------------
**lineprops
`.Line2D` properties that control the appearance of the lines.
See also `~.Axes.axhline`.
Examples
--------
See :doc:`/gallery/widgets/cursor`.
"""
def __init__(self, ax, horizOn=True, vertOn=True, useblit=False,
**lineprops):
AxesWidget.__init__(self, ax)
self.connect_event('motion_notify_event', self.onmove)
self.connect_event('draw_event', self.clear)
self.visible = True
self.horizOn = horizOn
self.vertOn = vertOn
self.useblit = useblit and self.canvas.supports_blit
if self.useblit:
lineprops['animated'] = True
self.lineh = ax.axhline(ax.get_ybound()[0], visible=False, **lineprops)
self.linev = ax.axvline(ax.get_xbound()[0], visible=False, **lineprops)
self.background = None
self.needclear = False
def clear(self, event):
"""Internal event handler to clear the cursor."""
if self.ignore(event):
return
if self.useblit:
self.background = self.canvas.copy_from_bbox(self.ax.bbox)
self.linev.set_visible(False)
self.lineh.set_visible(False)
def onmove(self, event):
"""Internal event handler to draw the cursor when the mouse moves."""
if self.ignore(event):
return
if not self.canvas.widgetlock.available(self):
return
if event.inaxes != self.ax:
self.linev.set_visible(False)
self.lineh.set_visible(False)
if self.needclear:
self.canvas.draw()
self.needclear = False
return
self.needclear = True
if not self.visible:
return
self.linev.set_xdata((event.xdata, event.xdata))
self.lineh.set_ydata((event.ydata, event.ydata))
self.linev.set_visible(self.visible and self.vertOn)
self.lineh.set_visible(self.visible and self.horizOn)
self._update()
def _update(self):
if self.useblit:
if self.background is not None:
self.canvas.restore_region(self.background)
self.ax.draw_artist(self.linev)
self.ax.draw_artist(self.lineh)
self.canvas.blit(self.ax.bbox)
else:
self.canvas.draw_idle()
return False
自定义十字光标实现
简易十字光标实现
首先在 Cursor类的构造方法__init__中，构造了十字光标的横线、竖线和坐标显示；然后在on_mouse_move方法中，根据事件数据更新横竖线和坐标显示，最后在调用时，通过mpl_connect方法绑定on_mouse_move方法和鼠标移动事件'motion_notify_event'。
import matplotlib.pyplot as plt
import numpy as np
class Cursor:
"""
A cross hair cursor.
"""
def __init__(self, ax):
self.ax = ax
self.horizontal_line = ax.axhline(color='k', lw=0.8, ls='--')
self.vertical_line = ax.axvline(color='k', lw=0.8, ls='--')
# text location in axes coordinates
self.text = ax.text(0.72, 0.9, '', transform=ax.transAxes)
def set_cross_hair_visible(self, visible):
need_redraw = self.horizontal_line.get_visible() != visible
self.horizontal_line.set_visible(visible)
self.vertical_line.set_visible(visible)
self.text.set_visible(visible)
return need_redraw
def on_mouse_move(self, event):
if not event.inaxes:
need_redraw = self.set_cross_hair_visible(False)
if need_redraw:
self.ax.figure.canvas.draw()
else:
self.set_cross_hair_visible(True)
x, y = event.xdata, event.ydata
# update the line positions
self.horizontal_line.set_ydata(y)
self.vertical_line.set_xdata(x)
self.text.set_text('x=%1.2f, y=%1.2f' % (x, y))
self.ax.figure.canvas.draw()
x = np.arange(0, 1, 0.01)
y = np.sin(2 * 2 * np.pi * x)
fig, ax = plt.subplots()
ax.set_title('Simple cursor')
ax.plot(x, y, 'o')
cursor = Cursor(ax)
#关键部分，绑定鼠标移动事件处理
fig.canvas.mpl_connect('motion_notify_event', cursor.on_mouse_move)
plt.show()
优化十字光标实现
在简易实现中，每次鼠标移动时，都会重绘整个图像，这样效率比较低。
在优化实现中，每次鼠标移动时，只重绘光标和坐标显示，背景图像不再重绘。
import matplotlib.pyplot as plt
import numpy as np
class BlittedCursor:
"""
A cross hair cursor using blitting for faster redraw.
"""
def __init__(self, ax):
self.ax = ax
self.background = None
self.horizontal_line = ax.axhline(color='k', lw=0.8, ls='--')
self.vertical_line = ax.axvline(color='k', lw=0.8, ls='--')
# text location in axes coordinates
self.text = ax.text(0.72, 0.9, '', transform=ax.transAxes)
self._creating_background = False
ax.figure.canvas.mpl_connect('draw_event', self.on_draw)
def on_draw(self, event):
self.create_new_background()
def set_cross_hair_visible(self, visible):
need_redraw = self.horizontal_line.get_visible() != visible
self.horizontal_line.set_visible(visible)
self.vertical_line.set_visible(visible)
self.text.set_visible(visible)
return need_redraw
def create_new_background(self):
if self._creating_background:
# discard calls triggered from within this function
return
self._creating_background = True
self.set_cross_hair_visible(False)
self.ax.figure.canvas.draw()
self.background = self.ax.figure.canvas.copy_from_bbox(self.ax.bbox)
self.set_cross_hair_visible(True)
self._creating_background = False
def on_mouse_move(self, event):
if self.background is None:
self.create_new_background()
if not event.inaxes:
need_redraw = self.set_cross_hair_visible(False)
if need_redraw:
self.ax.figure.canvas.restore_region(self.background)
self.ax.figure.canvas.blit(self.ax.bbox)
else:
self.set_cross_hair_visible(True)
# update the line positions
x, y = event.xdata, event.ydata
self.horizontal_line.set_ydata(y)
self.vertical_line.set_xdata(x)
self.text.set_text('x=%1.2f, y=%1.2f' % (x, y))
self.ax.figure.canvas.restore_region(self.background)
self.ax.draw_artist(self.horizontal_line)
self.ax.draw_artist(self.vertical_line)
self.ax.draw_artist(self.text)
self.ax.figure.canvas.blit(self.ax.bbox)
x = np.arange(0, 1, 0.01)
y = np.sin(2 * 2 * np.pi * x)
fig, ax = plt.subplots()
ax.set_title('Blitted cursor')
ax.plot(x, y, 'o')
blitted_cursor = BlittedCursor(ax)
fig.canvas.mpl_connect('motion_notify_event', blitted_cursor.on_mouse_move)
plt.show()
捕捉数据十字光标实现
在前面的两种实现中，鼠标十字光标可以随意移动。在本实现中，十字光标只会出现在离鼠标x坐标最近的数据点上。
import matplotlib.pyplot as plt
import numpy as np
class SnappingCursor:
"""
A cross hair cursor that snaps to the data point of a line, which is
closest to the *x* position of the cursor.
For simplicity, this assumes that *x* values of the data are sorted.
"""
def __init__(self, ax, line):
self.ax = ax
self.horizontal_line = ax.axhline(color='k', lw=0.8, ls='--')
self.vertical_line = ax.axvline(color='k', lw=0.8, ls='--')
self.x, self.y = line.get_data()
self._last_index = None
# text location in axes coords
self.text = ax.text(0.72, 0.9, '', transform=ax.transAxes)
def set_cross_hair_visible(self, visible):
need_redraw = self.horizontal_line.get_visible() != visible
self.horizontal_line.set_visible(visible)
self.vertical_line.set_visible(visible)
self.text.set_visible(visible)
return need_redraw
def on_mouse_move(self, event):
if not event.inaxes:
self._last_index = None
need_redraw = self.set_cross_hair_visible(False)
if need_redraw:
self.ax.figure.canvas.draw()
else:
self.set_cross_hair_visible(True)
x, y = event.xdata, event.ydata
index = min(np.searchsorted(self.x, x), len(self.x) - 1)
if index == self._last_index:
return # still on the same data point. Nothing to do.
self._last_index = index
x = self.x[index]
y = self.y[index]
# update the line positions
self.horizontal_line.set_ydata(y)
self.vertical_line.set_xdata(x)
self.text.set_text('x=%1.2f, y=%1.2f' % (x, y))
self.ax.figure.canvas.draw()
x = np.arange(0, 1, 0.01)
y = np.sin(2 * 2 * np.pi * x)
fig, ax = plt.subplots()
ax.set_title('Snapping cursor')
line, = ax.plot(x, y, 'o')
snap_cursor = SnappingCursor(ax, line)
fig.canvas.mpl_connect('motion_notify_event', snap_cursor.on_mouse_move)
plt.show()
参考资料
https://www.matplotlib.org.cn/gallery/misc/cursor_demo_sgskip.html
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