https://matplotlib.org/stable/gallery/event_handling/cursor_demo.html
Im trying to make a cross hair cursor with a annotation on the right axis to show the Y-value
everything works fine except when the artist / annotation is drawn outside the axis
keeps drawing the figure will work but my chart has many data which will cause 0.5 - 0.7sec for each draw, which is quite laggy for a cursor function self.ax.figure.canvas.draw()
my guess is when i save the background , "self.ax.bbox" is only saving the image for the thing inside the axis, that's why when it blit it doesnt work outside the axis? self.background = self.ax.figure.canvas.copy_from_bbox(self.ax.bbox)
I have many attempts but no luck...need some advices
below is the easy example (my plot will be a heavy one that i cannot keep calling the draw() on mousemove event) Im trying to make a smooth cross hair cursor with annotation on the right axis
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(0.95, 0, '', transform=ax.get_yaxis_transform())
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('y=%1.2f' % (y))
self.text.set_y(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()
