Returning mouse cursor coordinates in PyQtGraph

Question

I am new to PyQtGraph and want to use it for a speedy visualization of my data acquisition. Previously I was using matplotlib where redrawing the figure was my bottleneck. After transitioning to PyQtGraph, I am currently missing only one functionality of matplotlib. Namely, returning the x-, and y-coordinate of my mouse cursor.

How can I call/mimic the return of the x-, and y-coordinates of my mouse cursor in a plot made using PyQtGraph?

EDIT! - After implementing the tips of leongold, the code is able to return the mousecursor position without losing speed. The code is the following:

import numpy
import pyqtgraph as pg
from pyqtgraph.Qt import QtGui, QtCore

def gaussian(A, B, x):
  return A * numpy.exp(-(x/(2. * B))**2.)

def mouseMoved(evt):
  mousePoint = p.vb.mapSceneToView(evt[0])
  label.setText("<span style='font-size: 14pt; color: white'> x = %0.2f, <span style='color: white'> y = %0.2f</span>" % (mousePoint.x(), mousePoint.y()))


# Initial data frame
x = numpy.linspace(-5., 5., 10000)
y = gaussian(5., 0.2, x)


# Generate layout
win = pg.GraphicsWindow()
label = pg.LabelItem(justify = "right")
win.addItem(label)

p = win.addPlot(row = 1, col = 0)

plot = p.plot(x, y, pen = "y")

proxy = pg.SignalProxy(p.scene().sigMouseMoved, rateLimit=60, slot=mouseMoved)

# Update layout with new data
i = 0
while i < 500:
  noise = numpy.random.normal(0, .2, len(y))
  y_new = y + noise

  plot.setData(x, y_new, pen = "y", clear = True)
  p.enableAutoRange("xy", False)

  pg.QtGui.QApplication.processEvents()

  i += 1

win.close()

Answer 1

You need to setup a pyqtgraph.SignalProxy and connect it to a callback:

if p is your plot, it'll look like: pyqtgraph.SignalProxy(p.scene().sigMouseMoved, rateLimit=60, slot=callback)

Whenever the mouse is moved over the plot, the callback is called with an event as an argument, i.e. callback(event). event[0] holds a positional argument you pass to p.vb.mapSceneToView(position).x() for x value and p.vb.mapSceneToView(position).y() for y value.