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
classCursor(AxesWidget):
"""
Acrosshaircursorthatspanstheaxesandmoveswithmousecursor.
Forthecursortoremainresponsiveyoumustkeepareferencetoit.
Parameters
----------
ax:`matplotlib.axes.Axes`
The`~.axes.Axes`toattachthecursorto.
horizOn:bool,default:True
Whethertodrawthehorizontalline.
vertOn:bool,default:True
Whethertodrawtheverticalline.
useblit:bool,default:False
Useblittingforfasterdrawingifsupportedbythebackend.
OtherParameters
----------------
**lineprops
`.Line2D`propertiesthatcontroltheappearanceofthelines.
Seealso`~.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=useblitandself.canvas.supports_blit
ifself.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
defclear(self,event):
"""Internaleventhandlertoclearthecursor."""
ifself.ignore(event):
return
ifself.useblit:
self.background=self.canvas.copy_from_bbox(self.ax.bbox)
self.linev.set_visible(False)
self.lineh.set_visible(False)
defonmove(self,event):
"""Internaleventhandlertodrawthecursorwhenthemousemoves."""
ifself.ignore(event):
return
ifnotself.canvas.widgetlock.available(self):
return
ifevent.inaxes!=self.ax:
self.linev.set_visible(False)
self.lineh.set_visible(False)
ifself.needclear:
self.canvas.draw()
self.needclear=False
return
self.needclear=True
ifnotself.visible:
return
self.linev.set_xdata((event.xdata,event.xdata))
self.lineh.set_ydata((event.ydata,event.ydata))
self.linev.set_visible(self.visibleandself.vertOn)
self.lineh.set_visible(self.visibleandself.horizOn)
self._update()
def_update(self):
ifself.useblit:
ifself.backgroundisnotNone:
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()
returnFalse
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'。
importmatplotlib.pyplotasplt
importnumpyasnp
classCursor:
"""
Acrosshaircursor.
"""
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='--')
#textlocationinaxescoordinates
self.text=ax.text(0.72,0.9,'',transform=ax.transAxes)
defset_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)
returnneed_redraw
defon_mouse_move(self,event):
ifnotevent.inaxes:
need_redraw=self.set_cross_hair_visible(False)
ifneed_redraw:
self.ax.figure.canvas.draw()
else:
self.set_cross_hair_visible(True)
x,y=event.xdata,event.ydata
#updatethelinepositions
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('Simplecursor')
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。
importmatplotlib.pyplotasplt
importnumpyasnp
classBlittedCursor:
"""
Acrosshaircursorusingblittingforfasterredraw.
"""
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='--')
#textlocationinaxescoordinates
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)
defon_draw(self,event):
self.create_new_background()
defset_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)
returnneed_redraw
defcreate_new_background(self):
ifself._creating_background:
#discardcallstriggeredfromwithinthisfunction
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
defon_mouse_move(self,event):
ifself.backgroundisNone:
self.create_new_background()
ifnotevent.inaxes:
need_redraw=self.set_cross_hair_visible(False)
ifneed_redraw:
self.ax.figure.canvas.restore_region(self.background)
self.ax.figure.canvas.blit(self.ax.bbox)
else:
self.set_cross_hair_visible(True)
#updatethelinepositions
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('Blittedcursor')
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。
importmatplotlib.pyplotasplt
importnumpyasnp
classSnappingCursor:
"""
Acrosshaircursorthatsnapstothedatapointofaline,whichis
closesttothe*x*positionofthecursor.
Forsimplicity,thisassumesthat*x*valuesofthedataaresorted.
"""
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
#textlocationinaxescoords
self.text=ax.text(0.72,0.9,'',transform=ax.transAxes)
defset_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)
returnneed_redraw
defon_mouse_move(self,event):
ifnotevent.inaxes:
self._last_index=None
need_redraw=self.set_cross_hair_visible(False)
ifneed_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)
ifindex==self._last_index:
return#stillonthesamedatapoint.Nothingtodo.
self._last_index=index
x=self.x[index]
y=self.y[index]
#updatethelinepositions
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('Snappingcursor')
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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