.. DO NOT EDIT. .. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY. .. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE: .. "gallery/event_handling/cursor_demo.py" .. LINE NUMBERS ARE GIVEN BELOW. .. only:: html .. meta:: :keywords: codex .. note:: :class: sphx-glr-download-link-note :ref:`Go to the end ` to download the full example code .. rst-class:: sphx-glr-example-title .. _sphx_glr_gallery_event_handling_cursor_demo.py: ================= 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 .. redirect-from:: /gallery/misc/cursor_demo .. GENERATED FROM PYTHON SOURCE LINES 27-82 .. code-block:: Python import matplotlib.pyplot as plt import numpy as np from matplotlib.backend_bases import MouseEvent 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(f'x={x:1.2f}, y={y:1.2f}') 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) # Simulate a mouse move to (0.5, 0.5), needed for online docs t = ax.transData MouseEvent( "motion_notify_event", ax.figure.canvas, *t.transform((0.5, 0.5)) )._process() .. image-sg:: /gallery/event_handling/images/sphx_glr_cursor_demo_001.png :alt: Simple cursor :srcset: /gallery/event_handling/images/sphx_glr_cursor_demo_001.png, /gallery/event_handling/images/sphx_glr_cursor_demo_001_2_00x.png 2.00x :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 83-94 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'``. .. GENERATED FROM PYTHON SOURCE LINES 94-169 .. code-block:: Python 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(f'x={x:1.2f}, y={y:1.2f}') 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) # Simulate a mouse move to (0.5, 0.5), needed for online docs t = ax.transData MouseEvent( "motion_notify_event", ax.figure.canvas, *t.transform((0.5, 0.5)) )._process() .. image-sg:: /gallery/event_handling/images/sphx_glr_cursor_demo_002.png :alt: Blitted cursor :srcset: /gallery/event_handling/images/sphx_glr_cursor_demo_002.png, /gallery/event_handling/images/sphx_glr_cursor_demo_002_2_00x.png 2.00x :class: sphx-glr-single-img .. GENERATED FROM PYTHON SOURCE LINES 170-180 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. .. GENERATED FROM PYTHON SOURCE LINES 180-243 .. code-block:: Python 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(f'x={x:1.2f}, y={y:1.2f}') 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) # Simulate a mouse move to (0.5, 0.5), needed for online docs t = ax.transData MouseEvent( "motion_notify_event", ax.figure.canvas, *t.transform((0.5, 0.5)) )._process() plt.show() .. image-sg:: /gallery/event_handling/images/sphx_glr_cursor_demo_003.png :alt: Snapping cursor :srcset: /gallery/event_handling/images/sphx_glr_cursor_demo_003.png, /gallery/event_handling/images/sphx_glr_cursor_demo_003_2_00x.png 2.00x :class: sphx-glr-single-img .. rst-class:: sphx-glr-timing **Total running time of the script:** (0 minutes 1.130 seconds) .. _sphx_glr_download_gallery_event_handling_cursor_demo.py: .. only:: html .. container:: sphx-glr-footer sphx-glr-footer-example .. container:: sphx-glr-download sphx-glr-download-jupyter :download:`Download Jupyter notebook: cursor_demo.ipynb ` .. container:: sphx-glr-download sphx-glr-download-python :download:`Download Python source code: cursor_demo.py ` .. only:: html .. rst-class:: sphx-glr-signature `Gallery generated by Sphinx-Gallery `_