[ENH]: matplotlib.widgets.PolygonSelector widget initial cursor position at data rather than (0,0)

[rtrwalker]

Problem

I'm trying this demo of matplotlib.widgets.PolygonSelector widget: Select indices from a collection using polygon selector. The demo as is, is fine because the data is close to (0,0). However, if the data is not near the origin (e.g. add 500 to grid_x and grid_y in the demo) then the PolygonSelector cursor starts at (0,0) when the figure appears and the data is far off and appears small so I have to always zoom in before selecting points. It would be nice if the initial cursor position was relevant to the data.

Proposed solution

In the PolygonSelector widget init method replace:
self._xs, self._ys = [0], [0]
with
self._xs, self._ys = [sum(ax.get_xlim()) / 2], [sum(ax.get_ylim()) / 2
Then the cursor will be in the middle of the axes object that is past to the PolygonSelector initiator.

[timhoffm]

👍 Do you want to make a pull request?

[Kaustbh]

Hi, can I make a PR?

[tacaswell]

@Kaustbh please do.

[Kaustbh]

@rtrwalker can you please tell me how to reproduce the problem, I am not able to reproduce it.

[rtrwalker]

@Kaustbh copy the example code from Select indices from a collection using polygon selector . Add 500 (or some large number) to grid_x and grid_y .

if __name__ == '__main__':
    import matplotlib.pyplot as plt

    fig, ax = plt.subplots()
    grid_size = 5
    grid_x = np.tile(np.arange(grid_size), grid_size)+500
    grid_y = np.repeat(np.arange(grid_size), grid_size)+500

[Kaustbh]

Its giving me output like this,
version = 3.9.0
backend = "QtAgg"

what is your matplotlib version ?