How to get mousedown position in ui.matplotlib

[nghia-vo]

Question

I would like to get the mouse position when clicking on an image displayed by ui.matplotlib. How can I achieve that?

import numpy as np
from nicegui import ui, events

def mouse_handler(e: events.MouseEventArguments):
    # How to get mouse position here
    ui.notify("Mouse position is")

main_plot = ui.matplotlib(figsize=(8, 6))
main_plot.on("click", mouse_handler)
mat = np.random.rand(100, 100)
ax = main_plot.figure.gca()
ax.imshow(mat)
main_plot.update()
ui.run()

[falkoschindler]

Hi @nghia-vo,

The event arguments e contain various attributes:

with ui.matplotlib(figsize=(8, 6)).on('click', lambda e: print(e.args)).figure as fig:
    fig.gca().imshow(np.random.rand(100, 100))

Output:

{'isTrusted': True, '_vts': 1715579733809, 'pointerId': 1, 'width': 1, 'height': 1, 'pressure': 0, 'tiltX': 0, 'tiltY': 0, 'azimuthAngle': 0, 'altitudeAngle': 1.5707963267948966, 'tangentialPressure': 0, 'twist': 0, 'pointerType': 'mouse', 'isPrimary': False, 'screenX': 464, 'screenY': 314, 'clientX': 464, 'clientY': 189, 'ctrlKey': False, 'shiftKey': False, 'altKey': False, 'metaKey': False, 'button': 0, 'buttons': 0, 'relatedTarget': None, 'pageX': 464, 'pageY': 189, 'x': 464, 'y': 189, 'offsetX': 449, 'offsetY': 173, 'movementX': 0, 'movementY': 0, 'fromElement': None, 'toElement': None, 'layerX': 464, 'layerY': 189, 'detail': 1, 'sourceCapabilities': {}, 'which': 1, 'type': 'click', 'eventPhase': 3, 'bubbles': True, 'cancelable': True, 'defaultPrevented': False, 'composed': True, 'timeStamp': 583.8999999761581, 'returnValue': True, 'cancelBubble': False, 'NONE': 0, 'CAPTURING_PHASE': 1, 'AT_TARGET': 2, 'BUBBLING_PHASE': 3}

Unfortunately the mouse coordinates are in screen pixels and not in the data coordinate system 0..100. I'm not sure if there's a way to convert them reliably though.

[nghia-vo]

Thanks Falko, that's useful information. I can go from here.