[Matplotlib-users] Graphics issues when combining matplotlib widgets: Spanselector, cursor, fill_between:

[Delosari <lat...@gm...>]

Hi, I have found minor graphical issues while using the spanselector, cursor
and fill_between widgets, which I would like to share with you.

All of them, can be experienced in this code (which I took from the
matplolib example)

"""
The SpanSelector is a mouse widget to select a xmin/xmax range and plot the
detail view of the selected region in the lower axes
"""
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import SpanSelector
import matplotlib.widgets as widgets

Fig = plt.figure(figsize=(8,6))
Fig.set_facecolor('w')
Fig.set
Ax = Fig.add_subplot(211)


x = np.arange(0.0, 5.0, 0.01)
y = np.sin(2*np.pi*x) + 0.5*np.random.randn(len(x))

Ax.plot(x, y, '-')
Ax.set_ylim(-2,2)
Ax.set_title('Press left mouse button and drag to test')

RegionIndices = []

ax2 = Fig.add_subplot(212)
line2, = ax2.plot(x, y, '-')


def onselect(xmin, xmax):
    if len(RegionIndices) == 2:
        Ax.fill_between(x[:], 0.0, y[:],facecolor='White',alpha=1)
        del RegionIndices[:]

                    
    indmin, indmax = np.searchsorted(x, (xmin, xmax))
    indmax = min(len(x)-1, indmax)
    
    Ax.fill_between(x[indmin:indmax], 0.0,
y[indmin:indmax],facecolor='Blue',alpha=0.30)
    
    thisx = x[indmin:indmax]
    thisy = y[indmin:indmax]
    line2.set_data(thisx, thisy)
    ax2.set_xlim(thisx[0], thisx[-1])
    ax2.set_ylim(thisy.min(), thisy.max())
    Fig.canvas.draw()
    
    RegionIndices.append(xmin)
    RegionIndices.append(xmax)

# set useblit True on gtkagg for enhanced performance
span = SpanSelector(Ax, onselect, 'horizontal', useblit =
True,rectprops=dict(alpha=0.5, facecolor='purple') )
cursor = widgets.Cursor(Ax, color="red", linewidth = 1, useblit = True)

plt.show()

I wonder if there is some way to avoid these two small issues:

1) You can see that when you select a region the spanselector box (purple)
glitches. In this code the effect is barely noticeable but on plots with
many lines is quite annoying (I have tried all the trueblit combinations to
not effect)

2) In this code when you select a region, the area in the upper plot between
the line and the horizontal axis is filled in blue. When you select a new
region the old area is filled in white (to clear it) and the new one is
filled with blue again. However, when I do that the line plotted, as well
as, the horizontal axis, become thicker... Is there a way to clear such a
region (generated with fill_between) without this happening... Or is it
necessary to replot the graph? Initially, I am  against doing this since I
have a well structured code and importing all the data again into the
spanselector method seems a bit messy... Which is the right way in python to
delete selected regions of a plot?

Any advice would be most welcome




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