QCursor::setPos makes cursor inactive for ~200ms

[trhaynes]

Hi there,

I have some code that uses a QTimer to get the current cursor position every x milliseconds. Every n runs of this, it resets the cursor to the middle of the screen using the static QCursor::setPos(int x, int y). However, queries on the position of the cursor for around the next 200ms show it being in the middle of the screen, despite me flailing the mouse around wildly. You can even see it "stick" in the middle for a short while.

Does anyone know why this happens or how I can fix it?

I'm using PyQt with Qt 4.4 right now. Thanks for your help.

-tom

[wysota]

Can we see some code of yours?

[trhaynes]

Here is some code that illustrates what I am talking about:

import sys, os, xvis, time, math
from PyQt4.QtCore import *
from PyQt4.QtGui import *
 
class Driver(QWidget):
  def __init__(self, parent):
    QWidget.__init__(self, parent)
    self.setMouseTracking(True)
    self.last_cursor = QCursor.pos()
    self.last_update = 0
    self.reset_interval = 100
    self.middle_x = app.desktop().screenGeometry().width() / 2.0
    self.middle_y = app.desktop().screenGeometry().height() / 2.0
 
  def get_cursor_change(self):
    """Return (x,y) tuple of cursor change"""
    self.last_update += 1
    cursor = QCursor.pos()
    diff = cursor - self.last_cursor
    self.last_cursor = cursor
    if self.last_update > self.reset_interval:
        # move cursor to middle of screen
        QCursor.setPos(self.middle_x, self.middle_y)
        self.last_cursor = QPoint(self.middle_x, self.middle_y)
        self.last_update = 0
    return (diff.x(), diff.y())
 
  def mouseMoveEvent(self, event):    
    event.accept()
 
class MainWindow(QMainWindow):
  def __init__(self, parent=None):
    QMainWindow.__init__(self, parent)    
 
    self.driver = Driver(self)
    self.setCentralWidget(self.driver)
 
    # run loop
    timer = QTimer(self)
    self.connect(timer, SIGNAL("timeout()"), self.update)
    timer.start(50) 
 
  def update(self):
    """Gets called each iteration"""  
    cursor_change =  self.driver.get_cursor_change()
    print cursor_change
 
if __name__ == "__main__":
  app = QApplication(sys.argv)
  mainwindow = MainWindow()
  mainwindow.show()
  mainwindow.raise_()
  sys.exit(app.exec_())

import sys, os, xvis, time, math
from PyQt4.QtCore import *
from PyQt4.QtGui import *
    
class Driver(QWidget):
  def __init__(self, parent):
    QWidget.__init__(self, parent)
    self.setMouseTracking(True)
    self.last_cursor = QCursor.pos()
    self.last_update = 0
    self.reset_interval = 100
    self.middle_x = app.desktop().screenGeometry().width() / 2.0
    self.middle_y = app.desktop().screenGeometry().height() / 2.0
 
  def get_cursor_change(self):
    """Return (x,y) tuple of cursor change"""
    self.last_update += 1
    cursor = QCursor.pos()
    diff = cursor - self.last_cursor
    self.last_cursor = cursor
    if self.last_update > self.reset_interval:
        # move cursor to middle of screen
        QCursor.setPos(self.middle_x, self.middle_y)
        self.last_cursor = QPoint(self.middle_x, self.middle_y)
        self.last_update = 0
    return (diff.x(), diff.y())
    
  def mouseMoveEvent(self, event):    
    event.accept()

class MainWindow(QMainWindow):
  def __init__(self, parent=None):
    QMainWindow.__init__(self, parent)    
    
    self.driver = Driver(self)
    self.setCentralWidget(self.driver)

    # run loop
    timer = QTimer(self)
    self.connect(timer, SIGNAL("timeout()"), self.update)
    timer.start(50) 
    
  def update(self):
    """Gets called each iteration"""  
    cursor_change =  self.driver.get_cursor_change()
    print cursor_change
    
if __name__ == "__main__":
  app = QApplication(sys.argv)
  mainwindow = MainWindow()
  mainwindow.show()
  mainwindow.raise_()
  sys.exit(app.exec_())

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and here is some sample output:

...
(0, 45)
(-56, 63)
(-49, 18)
(-59, -39)
(-11, -98)
(51, -30)
(98, 30)
(44, 68)
(-59, 60)
(-96, 19)
(0, 0)
(0, 0)
(0, 0)
(0, 0)
(0, 0)
(4, 91)
(-23, 44)
(-54, 3)
(-98, -44)
(-52, -86)
(43, -76)
(63, -3)
(56, 47)
(5, 84)
(-68, 72)
(-83, 18)
(-109, -34)
(-61, -52)
(18, -44)
...

...
(0, 45)
(-56, 63)
(-49, 18)
(-59, -39)
(-11, -98)
(51, -30)
(98, 30)
(44, 68)
(-59, 60)
(-96, 19)
(0, 0)
(0, 0)
(0, 0)
(0, 0)
(0, 0)
(4, 91)
(-23, 44)
(-54, 3)
(-98, -44)
(-52, -86)
(43, -76)
(63, -3)
(56, 47)
(5, 84)
(-68, 72)
(-83, 18)
(-109, -34)
(-61, -52)
(18, -44)
...

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The above is when moving the mouse around constantly. You can see the (0,0)s occur right after the mouse is reset to the middle.

Thanks for your help.

-tom