Skip to content

Rewrite cursor example to include speedup possibilities #15644

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Jan 13, 2020
Merged

Rewrite cursor example to include speedup possibilities #15644

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
219 changes: 219 additions & 0 deletions examples/misc/cursor_demo.py
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,219 @@
"""
=================
Cross hair cursor
=================

This example adds a cross hair as a data cursor. The cross hair is
implemented as regular line objects that are updated on mouse move.

We show three implementations:

1) A simple cursor implementation that redraws the figure on every mouse move.
This is a bit slow and you may notice some lag of the cross hair movement.
2) A cursor that uses blitting for speedup of the rendering.
3) A cursor that snaps to data points.

Faster cursoring is possible using native GUI drawing, as in
:doc:`/gallery/user_interfaces/wxcursor_demo_sgskip`.

The mpldatacursor__ and mplcursors__ third-party packages can be used to
achieve a similar effect.

__ https://github.com/joferkington/mpldatacursor
__ https://github.com/anntzer/mplcursors
"""

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)
fig.canvas.mpl_connect('motion_notify_event', cursor.on_mouse_move)


##############################################################################
# Faster redrawing using blitting
# """""""""""""""""""""""""""""""
# This technique stores the rendered plot as a background image. Only the
# changed artists (cross hair lines and text) are rendered anew. They are
# combined with the background using blitting.
#
# This technique is significantly faster. It requires a bit more setup because
# the background has to be stored without the cross hair lines (see
# ``create_new_background()``). Additionally, a new background has to be
# created whenever the figure changes. This is achieved by connecting to the
# ``'draw_event'``.

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)


##############################################################################
# Snapping to data points
# """""""""""""""""""""""
# The following cursor snaps its position to the data points of a `.Line2D`
# object.
#
# To save unnecessary redraws, the index of the last indicated data point is
# saved in ``self._last_index``. A redraw is only triggered when the mouse
# moves far enough so that another data point must be selected. This reduces
# the lag due to many redraws. Of course, blitting could still be added on top
# for additional speedup.

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 is 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()
91 changes: 0 additions & 91 deletions examples/misc/cursor_demo_sgskip.py
View file
Open in desktop

This file was deleted.