Returning mouse cursor coordinates in PyQtGraph

[Sebastiaan Greveling]

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 making the transition 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?

I have had a look at the HoverEvent documentation. However, with my code I am not able to figure out how to call these functions. All the errors I produce tell me that the attribute I am trying to call is not contained by the function I am using.

A simple version of the code I will be using for my data acquisition is found below:

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

x = numpy.linspace(-2 * numpy.pi, 2 * numpy.pi, 1000)
y = numpy.cos(x)

# Plot
win = pg.GraphicsWindow()
win.resize(800, 800)

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

i = 0
while i < 350:
  noise = numpy.random.normal(0, 1, len(y))
  y_new = y + noise

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

  pg.QtGui.QApplication.processEvents()

  i += 1
win.close()

[shaera...@gmail.com]

I did it this way: override the mouseMoveEvent().. I dont no if there is a better way to do this .. 

class  graphicsLayoutWidget(pg.GraphicsLayoutWidget):

    def __init__(self):

        pg.GraphicsLayoutWidget.__init__(self)

        

    def mouseMoveEvent(self, event):

        print event.pos()

app = QtGui.QApplication([])

x = numpy.linspace(-2 * numpy.pi, 2 * numpy.pi, 1000)

y = numpy.cos(x)

# Plot

win = graphicsLayoutWidget()

win.show()

win.resize(800, 800)

p = win.addPlot()

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

i = 0

while 1:

  noise = numpy.random.normal(0, 1, len(y))

  y_new = y + noise

  p.plot(x, y_new, pen = "y", clear = True)

  p.enableAutoRange("xy", False)

  i += 1

  pg.QtGui.QApplication.processEvents()

win.close()

[Vincent Le Saux]

Hi,

I think you should have a look at the crosshair.py example. Another (and better to my opinion) solution is proposed.

Vincent

[Sebastiaan Greveling]

Thank you very much Vincent. Until your remark I only had a very quick look at the examples. With the crosshair.py example I am now able to return the mouse position without loosing plotting speed. The piece of code I have now 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()

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[Vincent Le Saux]

Thanks for sharing your piece of code. It could be useful for other users!

Vincent