|
| 1 | +""" |
| 2 | +================= |
| 3 | +Cross hair cursor |
| 4 | +================= |
| 5 | +
|
| 6 | +This example adds a cross hair as a data cursor. The cross hair is |
| 7 | +implemented as regular line objects that are updated on mouse move. |
| 8 | +
|
| 9 | +We show three implementations: |
| 10 | +
|
| 11 | +1) A simple cursor implementation that redraws the figure on every mouse move. |
| 12 | + This is a bit slow and you may notice some lag of the cross hair movement. |
| 13 | +2) A cursor that uses blitting for speedup of the rendering. |
| 14 | +3) A cursor that snaps to data points. |
| 15 | +
|
| 16 | +Faster cursoring is possible using native GUI drawing, as in |
| 17 | +:doc:`/gallery/user_interfaces/wxcursor_demo_sgskip`. |
| 18 | +
|
| 19 | +The mpldatacursor__ and mplcursors__ third-party packages can be used to |
| 20 | +achieve a similar effect. |
| 21 | +
|
| 22 | +__ https://github.com/joferkington/mpldatacursor |
| 23 | +__ https://github.com/anntzer/mplcursors |
| 24 | +""" |
| 25 | + |
| 26 | +import matplotlib.pyplot as plt |
| 27 | +import numpy as np |
| 28 | + |
| 29 | + |
| 30 | +class Cursor: |
| 31 | + """ |
| 32 | + A cross hair cursor. |
| 33 | + """ |
| 34 | + def __init__(self, ax): |
| 35 | + self.ax = ax |
| 36 | + self.horizontal_line = ax.axhline(color='k', lw=0.8, ls='--') |
| 37 | + self.vertical_line = ax.axvline(color='k', lw=0.8, ls='--') |
| 38 | + # text location in axes coordinates |
| 39 | + self.text = ax.text(0.72, 0.9, '', transform=ax.transAxes) |
| 40 | + |
| 41 | + def set_cross_hair_visible(self, visible): |
| 42 | + need_redraw = self.horizontal_line.get_visible() != visible |
| 43 | + self.horizontal_line.set_visible(visible) |
| 44 | + self.vertical_line.set_visible(visible) |
| 45 | + self.text.set_visible(visible) |
| 46 | + return need_redraw |
| 47 | + |
| 48 | + def on_mouse_move(self, event): |
| 49 | + if not event.inaxes: |
| 50 | + need_redraw = self.set_cross_hair_visible(False) |
| 51 | + if need_redraw: |
| 52 | + self.ax.figure.canvas.draw() |
| 53 | + else: |
| 54 | + self.set_cross_hair_visible(True) |
| 55 | + x, y = event.xdata, event.ydata |
| 56 | + # update the line positions |
| 57 | + self.horizontal_line.set_ydata(y) |
| 58 | + self.vertical_line.set_xdata(x) |
| 59 | + self.text.set_text('x=%1.2f, y=%1.2f' % (x, y)) |
| 60 | + self.ax.figure.canvas.draw() |
| 61 | + |
| 62 | + |
| 63 | +x = np.arange(0, 1, 0.01) |
| 64 | +y = np.sin(2 * 2 * np.pi * x) |
| 65 | + |
| 66 | +fig, ax = plt.subplots() |
| 67 | +ax.set_title('Simple cursor') |
| 68 | +ax.plot(x, y, 'o') |
| 69 | +cursor = Cursor(ax) |
| 70 | +fig.canvas.mpl_connect('motion_notify_event', cursor.on_mouse_move) |
| 71 | + |
| 72 | + |
| 73 | +############################################################################## |
| 74 | +# Faster redrawing using blitting |
| 75 | +# """"""""""""""""""""""""""""""" |
| 76 | +# This technique stores the rendered plot as a background image. Only the |
| 77 | +# changed artists (cross hair lines and text) are rendered anew. They are |
| 78 | +# combined with the background using blitting. |
| 79 | +# |
| 80 | +# This technique is significantly faster. It requires a bit more setup because |
| 81 | +# the background has to be stored without the cross hair lines (see |
| 82 | +# ``create_new_background()``). Additionally, a new background has to be |
| 83 | +# created whenever the figure changes. This is achieved by connecting to the |
| 84 | +# ``'draw_event'``. |
| 85 | + |
| 86 | +class BlittedCursor: |
| 87 | + """ |
| 88 | + A cross hair cursor using blitting for faster redraw. |
| 89 | + """ |
| 90 | + def __init__(self, ax): |
| 91 | + self.ax = ax |
| 92 | + self.background = None |
| 93 | + self.horizontal_line = ax.axhline(color='k', lw=0.8, ls='--') |
| 94 | + self.vertical_line = ax.axvline(color='k', lw=0.8, ls='--') |
| 95 | + # text location in axes coordinates |
| 96 | + self.text = ax.text(0.72, 0.9, '', transform=ax.transAxes) |
| 97 | + self._creating_background = False |
| 98 | + ax.figure.canvas.mpl_connect('draw_event', self.on_draw) |
| 99 | + |
| 100 | + def on_draw(self, event): |
| 101 | + self.create_new_background() |
| 102 | + |
| 103 | + def set_cross_hair_visible(self, visible): |
| 104 | + need_redraw = self.horizontal_line.get_visible() != visible |
| 105 | + self.horizontal_line.set_visible(visible) |
| 106 | + self.vertical_line.set_visible(visible) |
| 107 | + self.text.set_visible(visible) |
| 108 | + return need_redraw |
| 109 | + |
| 110 | + def create_new_background(self): |
| 111 | + if self._creating_background: |
| 112 | + # discard calls triggered from within this function |
| 113 | + return |
| 114 | + self._creating_background = True |
| 115 | + self.set_cross_hair_visible(False) |
| 116 | + self.ax.figure.canvas.draw() |
| 117 | + self.background = self.ax.figure.canvas.copy_from_bbox(self.ax.bbox) |
| 118 | + self.set_cross_hair_visible(True) |
| 119 | + self._creating_background = False |
| 120 | + |
| 121 | + def on_mouse_move(self, event): |
| 122 | + if self.background is None: |
| 123 | + self.create_new_background() |
| 124 | + if not event.inaxes: |
| 125 | + need_redraw = self.set_cross_hair_visible(False) |
| 126 | + if need_redraw: |
| 127 | + self.ax.figure.canvas.restore_region(self.background) |
| 128 | + self.ax.figure.canvas.blit(self.ax.bbox) |
| 129 | + else: |
| 130 | + self.set_cross_hair_visible(True) |
| 131 | + # update the line positions |
| 132 | + x, y = event.xdata, event.ydata |
| 133 | + self.horizontal_line.set_ydata(y) |
| 134 | + self.vertical_line.set_xdata(x) |
| 135 | + self.text.set_text('x=%1.2f, y=%1.2f' % (x, y)) |
| 136 | + |
| 137 | + self.ax.figure.canvas.restore_region(self.background) |
| 138 | + self.ax.draw_artist(self.horizontal_line) |
| 139 | + self.ax.draw_artist(self.vertical_line) |
| 140 | + self.ax.draw_artist(self.text) |
| 141 | + self.ax.figure.canvas.blit(self.ax.bbox) |
| 142 | + |
| 143 | + |
| 144 | +x = np.arange(0, 1, 0.01) |
| 145 | +y = np.sin(2 * 2 * np.pi * x) |
| 146 | + |
| 147 | +fig, ax = plt.subplots() |
| 148 | +ax.set_title('Blitted cursor') |
| 149 | +ax.plot(x, y, 'o') |
| 150 | +blitted_cursor = BlittedCursor(ax) |
| 151 | +fig.canvas.mpl_connect('motion_notify_event', blitted_cursor.on_mouse_move) |
| 152 | + |
| 153 | + |
| 154 | +############################################################################## |
| 155 | +# Snapping to data points |
| 156 | +# """"""""""""""""""""""" |
| 157 | +# The following cursor snaps its position to the data points of a `.Line2D` |
| 158 | +# object. |
| 159 | +# |
| 160 | +# To save unnecessary redraws, the index of the last indicated data point is |
| 161 | +# saved in ``self._last_index``. A redraw is only triggered when the mouse |
| 162 | +# moves far enough so that another data point must be selected. This reduces |
| 163 | +# the lag due to many redraws. Of course, blitting could still be added on top |
| 164 | +# for additional speedup. |
| 165 | + |
| 166 | +class SnappingCursor: |
| 167 | + """ |
| 168 | + A cross hair cursor that snaps to the data point of a line, which is |
| 169 | + closest to the *x* position of the cursor. |
| 170 | +
|
| 171 | + For simplicity, this assumes that *x* values of the data is sorted. |
| 172 | + """ |
| 173 | + def __init__(self, ax, line): |
| 174 | + self.ax = ax |
| 175 | + self.horizontal_line = ax.axhline(color='k', lw=0.8, ls='--') |
| 176 | + self.vertical_line = ax.axvline(color='k', lw=0.8, ls='--') |
| 177 | + self.x, self.y = line.get_data() |
| 178 | + self._last_index = None |
| 179 | + # text location in axes coords |
| 180 | + self.text = ax.text(0.72, 0.9, '', transform=ax.transAxes) |
| 181 | + |
| 182 | + def set_cross_hair_visible(self, visible): |
| 183 | + need_redraw = self.horizontal_line.get_visible() != visible |
| 184 | + self.horizontal_line.set_visible(visible) |
| 185 | + self.vertical_line.set_visible(visible) |
| 186 | + self.text.set_visible(visible) |
| 187 | + return need_redraw |
| 188 | + |
| 189 | + def on_mouse_move(self, event): |
| 190 | + if not event.inaxes: |
| 191 | + self._last_index = None |
| 192 | + need_redraw = self.set_cross_hair_visible(False) |
| 193 | + if need_redraw: |
| 194 | + self.ax.figure.canvas.draw() |
| 195 | + else: |
| 196 | + self.set_cross_hair_visible(True) |
| 197 | + x, y = event.xdata, event.ydata |
| 198 | + index = min(np.searchsorted(self.x, x), len(self.x) - 1) |
| 199 | + if index == self._last_index: |
| 200 | + return # still on the same data point. Nothing to do. |
| 201 | + self._last_index = index |
| 202 | + x = self.x[index] |
| 203 | + y = self.y[index] |
| 204 | + # update the line positions |
| 205 | + self.horizontal_line.set_ydata(y) |
| 206 | + self.vertical_line.set_xdata(x) |
| 207 | + self.text.set_text('x=%1.2f, y=%1.2f' % (x, y)) |
| 208 | + self.ax.figure.canvas.draw() |
| 209 | + |
| 210 | + |
| 211 | +x = np.arange(0, 1, 0.01) |
| 212 | +y = np.sin(2 * 2 * np.pi * x) |
| 213 | + |
| 214 | +fig, ax = plt.subplots() |
| 215 | +ax.set_title('Snapping cursor') |
| 216 | +line, = ax.plot(x, y, 'o') |
| 217 | +snap_cursor = SnappingCursor(ax, line) |
| 218 | +fig.canvas.mpl_connect('motion_notify_event', snap_cursor.on_mouse_move) |
| 219 | +plt.show() |
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