Keypress event in Maya

839 views
Skip to first unread message

Alexey Vasilyev

unread,
May 26, 2018, 2:27:14 AM5/26/18
to Python Programming for Autodesk Maya
Hi.
I'm new to Maya programming.
I'm curious if it's possible to track keypress events in Maya main window using PySide or any other way?
For example, when cube primitive is selected, I want to be able to increase or decrease its subdivisions using Left and Right arrows. When it's not selected, I want arrow keys to function in the default way.
Thanks.

Marcus Ottosson

unread,
May 28, 2018, 8:57:54 AM5/28/18
to python_in...@googlegroups.com

Yes, this is possible.

from PySide import QtGui, QtCore

class MyEventHandler(QtCore.QObject):
  def eventFilter(self, target, event):
    if event.type() == event.KeyPress:
      print("That's a keypress")
    return super(MyEventHandler, self).eventFilter(target, event)

handler = MyEventHandler()

app = QtGui.QApplication.instance()
app.installEventFilter(handler)
# app.removeEventFilter(handler)

That would normally be fine, however if there is one object where you never want a (Python) event filter, it would be the QApplication or Maya’s MainWindow. Because what happens is that every single event in Maya which was previously highly optimised C++ now has to pass through your Python function. Which means that even if your function does nothing but pass the event through, it still has a significant effect on performance. For starters, you should notice that with this filter installed, navigating in the viewport suddenly has a slight delay. As if the click caused a minor lag before eventually allowing you to dolly the camera.

To put a picture in your head, here’s why.

Information Super Highway

--------------\                 /--------------->
-------------- \               /---------------->
---------------->-------------/----------------->
-------------- /              \----------------->
--------------/                \---------------->
      C++           Python             C++

Instead, what you should consider, if you are able, is installing an event filter not in QApplication or Maya’s main window, but in your widget.

class MyWidget(QtGui.QDialog):
  def __init__(self, parent=None):
    super(MyWidget, self).__init__(parent)

handler = MyEventHandler() 
mywidget = MyWidget()
mywidget.installEventFilter(handler)

But most preferably, would be to not use an event filter, and instead override the event handler called only on keypress events.

  class MyWidget(QtGui.QDialog):
  def __init__(self, parent=None):
    super(MyWidget, self).__init__(parent)

  def keyPressEvent(self, event):
    print("That's a press!")
    return super(MyWidget, self).keyPressEvent(event)

That way, there is zero overhead on any event handling, other than the one you override.

Hope it helps!

​

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_maya+unsub...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/python_inside_maya/c7024d27-4a67-448e-9e57-a873ff85dcbc%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Alexey Vasilyev

unread,
May 28, 2018, 3:25:36 PM5/28/18
to Python Programming for Autodesk Maya
Thanks, Markus, It definitely helps!
This is more or less what I've been trying to do. The Issue I have with this approach is that keypress tracking only works when the widget is in focus. I need my widget to track keypress events during my work in Maya viewport. As soon as  I switch focus from widget window to Maya viewport keypress tracking stops working. Which is not cool:) Is there any way to make the widget track keypress events regardless of what window is in focus?
Thanks.

vaillant...@gmail.com

unread,
Mar 3, 2020, 2:35:54 AM3/3/20
to Python Programming for Autodesk Maya
Some additional reflection on the topic:

Personally I don't notice any delay when filtering events from Maya's main window (Maya 2019).
IMHO I'm not sure this is as big of an issue as you may think it is. I need to test this more over time though.
Because my intution tells me events are usually very light and their load stay the same regardless of the scene complexity,
I'm really not sure why you would get noticable lag (even accounting for python overhead)

I haven't tried it yet but brave people might want to do event filtering inside their C++ plugin:
Since we can access Maya Qt core application from there as well.

#include <QtCore/QCoreApplication>
QCoreApplication *app = qApp;
void QObject::installEventFilter (QObject *filterObj)

Cheers

2018年5月28日月曜日 21時57分54秒 UTC+9 Marcus Ottosson:

Justin Israel

unread,
Mar 3, 2020, 2:43:47 AM3/3/20
to python_in...@googlegroups.com


On Tue, Mar 3, 2020, 8:35 PM <vaillant...@gmail.com> wrote:
Some additional reflection on the topic:

Personally I don't notice any delay when filtering events from Maya's main window (Maya 2019).
IMHO I'm not sure this is as big of an issue as you may think it is. I need to test this more over time though.
Because my intution tells me events are usually very light and their load stay the same regardless of the scene complexity,
I'm really not sure why you would get noticable lag (even accounting for python overhead)

Well Qt does document a warning about possible performance implications of filtering every event in the application even from the C++ side of things:

"It is also possible to filter all events for the entire application, by installing an event filter on the QApplication or QCoreApplication object. Such global event filters are called before the object-specific filters. This is very powerful, but it also slows down event delivery of every single event in the entire application; the other techniques discussed should generally be used instead."

So it would be reasonable to assume it would be far slower to put a python function into the path of the main event loop that is catching every event in the app. That would be every paint event. Maybe could impact a large amount of redrawing in the app? 

To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_m...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_m...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/python_inside_maya/31a77359-f8e0-466d-8c68-ea826575cecb%40googlegroups.com.

Marcus Ottosson

unread,
Mar 3, 2020, 5:14:56 AM3/3/20
to python_in...@googlegroups.com

Simple way to test whether this affects your usecase is to just put a timer inside of an empty event filter, installed onto the QApplication. I expect you’ll find a non-zero percentage of CPU time being occupied by this during simple tasks like mouse move, and for a much larger percentage to be occupied during playback when the entire application is redrawn per frame - guesstimating 2-5%.

That, multiplied by the number of vendors that install event filters onto the QApplication - your library, my library, two more libraries and so forth - is IMO enough to avoid it if you can. Especially taken into account that it is invisible to anyone but the author and very hard to debug. With “My scene is slow” as a starting point, where does one go from there?

And that’s not even considering what you do inside of the filter. I saw a timeline annotation tool recently, using an event filter to update a QPixmap whenever the timeline is redrawn. That’s rendering for 2-10 ms depending on the frame range, and is a cost paid by everything happening on draw, per frame, including animation rigs.

But it’s true we should have a test case. Odds are this varies between version of Maya, platform, maybe drivers and likely our perception and circumstances (i.e. whether 10 ms per frame is anything to worry about or not). If you do put something together @vaillant.rodolphe, it would be great if you could post it here so we can move from guesstimating to measuring.


To view this discussion on the web visit https://groups.google.com/d/msgid/python_inside_maya/CAPGFgA2m6NEVcLdt4x_HSViAmcOp8RaO%3D7Md14DUDmLwrp6L2Q%40mail.gmail.com.

vaillant...@gmail.com

unread,
Mar 3, 2020, 8:01:36 AM3/3/20
to Python Programming for Autodesk Maya
Oh I see, both of you raised very valid points. It seems the event filter is called for every screen refresh. Indeed anything in that callback will have a very critical impact on the final framerate.
Putting a timer inside an empty event filter gives me between 0ms and 1ms (Well the time it takes to call time.time() twice).
Given that this trick is much like an evil 'global' variable, I agree that it will make things very hard to troubleshoot not to mentioned that this hack may blow out of proportion if everyone is using it like you mentioned.

That being said, I think it fits my use case: I detect the 'SHIFT' key press event when I paint with a custom brush. The global event filter will only be 'slow' (~2-3ms tops) during a single press event of SHIFT and I remove the callback when my dialog window (used to configure the brush) is hidden. I haven't found any cleaner way to do this.

For instance, overriding keyPressEvent in my dialog window won't work since I loose focus when painting. I use MEL artUserPaintCtx to setup my custom brush. In maya pressing SHIFT will switch your current brush mode to its smooth variant, unfortunately I can't find any callback related to this option.

Thank you for your insight

2020年3月3日火曜日 19時14分56秒 UTC+9 Marcus Ottosson:
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_maya+unsub...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_maya+unsub...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_maya+unsub...@googlegroups.com.

Marcus Ottosson

unread,
Mar 3, 2020, 9:04:40 AM3/3/20
to python_in...@googlegroups.com

I remove the callback when my dialog window

This is key. Even if your filter was incredibly slow, it’s fine IMO because now it is apparent why it’s happening, and can be explicitly disabled (by closing the window). Good that you pointed this out. Most cases I’ve seen involved the filter being active at all times and that’s the stuff that can start to add up. Especially as you accumulate tens to hundreds of scripts at Maya startup over the course of a project.

I think generally, if it doesn’t affect playback like in this case, global event filters are harmless (and very useful). Most of the time though, if possible, local event handlers like mouseMoveEvent is much preferable, since it's only ever called for that one type of event.


To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_m...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_m...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_m...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_m...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/python_inside_maya/71e63b14-5402-495c-9d63-26b5f41b5650%40googlegroups.com.

Piotr Makal

unread,
Jul 16, 2020, 10:38:49 AM7/16/20
to Python Programming for Autodesk Maya
Just want to elaborate to what Justin have already brought up with his quote - there is significant difference between injecting event filters to Maya application vs. Maya main window.

Altering previous example provided by Marcus:
from PySide2 import QtCore
from maya.OpenMayaUI import MQtUtil
from shiboken2 import wrapInstance

class MyEventHandler(QtCore.QObject):
  def eventFilter(self, qobj, event):

    if event.type() == event.KeyPress:
      print("That's a keypress"
)
    return super(MyEventHandler, self).eventFilter(qobj, event)

handler = MyEventHandler()

app = QtCore.QCoreApplication.instance()
app.installEventFilter(handler)
# app.removeEventFilter(handler)

mayaWindow = wrapInstance(int(MQtUtil.mainWindow()), QWidget)
mayaWindow.installEventFilter(handler)
# mayaWindow.removeEventFilter(handler)
Since QCoreApplication is somewhat level above all GUI objects it acts as an "overlord" in terms of events, so even if you have a widget that eats key press events QCoreApplication will still see it and it will invoke eventFilter method for the object that was installed as event filter. The implication of this is that whenever you type anything to any text field (QTextEdit, QLineEdit, etc.) that eventFilter will be invoked.

When installing the same event filter for Maya main window it will only be affected if none of the child widgets consumed event beforehand.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_maya+unsub...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_maya+unsub...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_maya+unsub...@googlegroups.com.

--
You received this message because you are subscribed to the Google Groups "Python Programming for Autodesk Maya" group.
To unsubscribe from this group and stop receiving emails from it, send an email to python_inside_maya+unsub...@googlegroups.com.
Reply all
Reply to author
Forward
0 new messages